flowchart for literature review

• University of Texas Libraries

Literature Reviews

Steps in the literature review process.

• What is a literature review?
• Define your research question
• Determine inclusion and exclusion criteria
• Choose databases and search
• Review Results
• Synthesize Results
• Analyze Results
• Librarian Support
• You may need to some exploratory searching of the literature to get a sense of scope, to determine whether you need to narrow or broaden your focus
• Identify databases that provide the most relevant sources, and identify relevant terms (controlled vocabularies) to add to your search strategy
• Finalize your research question
• Think about relevant dates, geographies (and languages), methods, and conflicting points of view
• Conduct searches in the published literature via the identified databases
• Check to see if this topic has been covered in other discipline's databases
• Examine the citations of on-point articles for keywords, authors, and previous research (via references) and cited reference searching.
• Save your search results in a citation management tool (such as Zotero, Mendeley or EndNote)
• De-duplicate your search results
• Make sure that you've found the seminal pieces -- they have been cited many times, and their work is considered foundational 
• Check with your professor or a librarian to make sure your search has been comprehensive
• Evaluate the strengths and weaknesses of individual sources and evaluate for bias, methodologies, and thoroughness
• Group your results in to an organizational structure that will support why your research needs to be done, or that provides the answer to your research question  
• Develop your conclusions
• Are there gaps in the literature?
• Where has significant research taken place, and who has done it?
• Is there consensus or debate on this topic?
• Which methodological approaches work best?
• For example: Background, Current Practices, Critics and Proponents, Where/How this study will fit in 
• Organize your citations and focus on your research question and pertinent studies
• Compile your bibliography

Note: The first four steps are the best points at which to contact a librarian. Your librarian can help you determine the best databases to use for your topic, assess scope, and formulate a search strategy.

Videos Tutorials about Literature Reviews

This 4.5 minute video from Academic Education Materials has a Creative Commons License and a British narrator.

Recommended Reading

• Last Updated: Oct 26, 2022 2:49 PM
• URL: https://guides.lib.utexas.edu/literaturereviews

Literature Reviews: systematic searching at various levels

• for assignments
• for dissertations / theses
• Search strategy and searching
• Boolean Operators
• Search strategy template
• Screening & critiquing
• Citation Searching
• Google Scholar (with Lean Library)
• Resources for literature reviews
• Adding a referencing style to EndNote
• Exporting from different databases

PRISMA Flow Diagram

• Grey Literature
• What is the PRISMA Flow Diagram?
• How should I use it?
• When should I use it?
• PRISMA Links

The PRISMA Flow Diagram is a tool that can be used to record different stages of the literature search process--across multiple resources--and clearly show how a researcher went from, 'These are the databases I searched for my terms', to, 'These are the papers I'm going to talk about'.

PRISMA is not inflexible; it can be modified to suit the research needs of different people and, indeed, if you did a Google images search for the flow diagram you would see many different versions of the diagram being used. It's a good idea to have a look at a couple of those examples, and also to have a look at a couple of the articles on the PRISMA website to see how it has--and can--be used.

The PRISMA 2020 Statement was published in 2021. It consists of a  checklist  and a  flow diagram , and is intended to be accompanied by the PRISMA 2020 Explanation and Elaboration document.

In order to encourage dissemination of the PRISMA 2020 Statement, it has been published in several journals.

• How to use the PRISMA Flow Diagram for literature reviews A PDF [3.81MB] of the PowerPoint used to create the video. Each slide that has notes has a callout icon on the top right of the page which can be toggled on or off to make the notes visible.

There is also a PowerPoint version of the document but the file size is too large to upload here.

If you would like a copy, please email the Academic Librarians' mailbox from your university account to ask for it to be sent to you.

This is an example of how you  could  fill in the PRISMA flow diagram when conducting a new review. It is not a hard and fast rule but it should give you an idea of how you can use it.

For more detailed information, please have a look at this article:

Page, M.J., McKenzie, J.E., Bossuyt, P.M., Boutron, I., Hoffmann, T.C., Mulrow, C.D., Shamseer, L., Tetzlaff, J.M., Akl, E.A., Brennan, S.E., Chou, R., Glanville, J., Grimshaw, J.M., Hróbjartsson, A., Lalu, M.M., Li, T., Loder, E.W., Mayo-Wilson, E., McDonald, S., McGuinness, L.A., Stewart, L.A., Thomas, J., Tricco, A.C., Welch, V.A., Whiting,P. & Moher, D. (2021) 'The PRISMA 2020 statement: an updated guideline for reporting systematic reviews',  BMJ 372:(71). doi: 10.1136/bmj.n71 .

• Example of PRISMA 2020 diagram This is an example of *one* of the PRISMA 2020 flow diagrams you can use when reporting on your research process. There is more than one form that you can use so for other forms and advice please look at the PRISMA website for full details.

Start using the flow diagram as you start searching the databases you've decided upon. 

Make sure that you record the number of results that you found per database (before removing any duplicates) as per the filled in example. You can also do a Google images search for the PRISMA flow diagram to see the different ways in which people have used them to express their search processes.

• Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) PRISMA is an evidence-based minimum set of items for reporting in systematic reviews and meta-analyses. PRISMA focuses on the reporting of reviews evaluating randomized trials, but can also be used as a basis for reporting systematic reviews of other types of research, particularly evaluations of interventions.
• Prisma Flow Diagram This link will take you to downloadable Word and PDF copies of the flow diagram. These are modifiable and act as a starting point for you to record the process you engaged in from first search to the papers you ultimately discuss in your work. more... less... Do an image search on the internet for the flow diagram and you will be able to see all the different ways that people have modified the diagram to suit their personal research needs.

You can access the various checklists via the Equator website and the articles explaining PRISMA and its various extensions are available via PubMed.

Page, M.J., McKenzie, J.E., Bossuyt, P.M., Boutron, I., Hoffmann, T.C., Mulrow, C.D., Shamseer, L., Tetzlaff, J.M., Akl, E.A., Brennan, S.E., Chou, R., Glanville, J., Grimshaw, J.M., Hróbjartsson, A., Lalu, M.M., Li, T., Loder, E.W., Mayo-Wilson, E., McDonald, S., McGuinness, L.A., Stewart, L.A., Thomas, J., Tricco, A.C., Welch, V.A., Whiting, P., & Moher, D. (2021) ' The PRISMA 2020 statement: an updated guideline for reporting systematic reviews,'  BMJ .  Mar 29; 372:n71. doi: 10.1136/bmj.n71 .

Page, M.J., Moher, D., Bossuyt, P.M., Boutron, I., Hoffmann, T.C., Mulrow, C.D., Shamseer, L., Tetzlaff, J.M., Akl, E.A., Brennan, S.E., Chou, R., Glanville, J., Grimshaw, J.M., Hróbjartsson, A., Lalu, M.M., Li, T., Loder, E.W., Mayo-Wilson, E., McDonald, S., McGuinness, L.A., Stewart, L.A., Thomas, J., Tricco, A.C., Welch, V.A., Whiting, P., & McKenzie, J.E. (2021)  'PRISMA 2020 explanation and elaboration: updated guidance and exemplars for reporting systematic reviews',  BMJ, Mar 29; 372:n160. doi: 10.1136/bmj.n160 .

Page, M.J., McKenzie, J.E., Bossuyt, P.M., Boutron, I., Hoffmann, T.C., Mulrow, C.D., Shamseer, L., Tetzlaff, J.M., Akl, E.A., Brennan, S.E., Chou, R., Glanville, J., Grimshaw, J.M., Hróbjartsson, A., Lalu, M.M., Li, T., Loder, E.W., Mayo-Wilson, E., McDonald, S., McGuinness, L.A., Stewart, L.A., Thomas, J., Tricco, A.C., Welch, V.A., Whiting, P., & Moher, D. (2021) ' The PRISMA 2020 statement: An updated guideline for reporting systematic reviews,'  Journal of Clinical Epidemiology, June; 134:178-189. doi: 10.1016/j.jclinepi.2021.03.001 . 

• << Previous: Exporting from different databases
• Next: Grey Literature >>
• Last Updated: Apr 12, 2024 11:57 AM
• URL: https://libguides.derby.ac.uk/literature-reviews

How To Structure Your Literature Review

3 options to help structure your chapter.

By: Amy Rommelspacher (PhD) | Reviewer: Dr Eunice Rautenbach | November 2020 (Updated May 2023)

Writing the literature review chapter can seem pretty daunting when you’re piecing together your dissertation or thesis. As  we’ve discussed before , a good literature review needs to achieve a few very important objectives – it should:

• Demonstrate your knowledge of the research topic
• Identify the gaps in the literature and show how your research links to these
• Provide the foundation for your conceptual framework (if you have one)
• Inform your own  methodology and research design

To achieve this, your literature review needs a well-thought-out structure . Get the structure of your literature review chapter wrong and you’ll struggle to achieve these objectives. Don’t worry though – in this post, we’ll look at how to structure your literature review for maximum impact (and marks!).

But wait – is this the right time?

Deciding on the structure of your literature review should come towards the end of the literature review process – after you have collected and digested the literature, but before you start writing the chapter. 

In other words, you need to first develop a rich understanding of the literature before you even attempt to map out a structure. There’s no use trying to develop a structure before you’ve fully wrapped your head around the existing research.

Equally importantly, you need to have a structure in place before you start writing , or your literature review will most likely end up a rambling, disjointed mess. 

Importantly, don’t feel that once you’ve defined a structure you can’t iterate on it. It’s perfectly natural to adjust as you engage in the writing process. As we’ve discussed before , writing is a way of developing your thinking, so it’s quite common for your thinking to change – and therefore, for your chapter structure to change – as you write. 

Need a helping hand?

Like any other chapter in your thesis or dissertation, your literature review needs to have a clear, logical structure. At a minimum, it should have three essential components – an  introduction , a  body   and a  conclusion . 

Let’s take a closer look at each of these.

1: The Introduction Section

Just like any good introduction, the introduction section of your literature review should introduce the purpose and layout (organisation) of the chapter. In other words, your introduction needs to give the reader a taste of what’s to come, and how you’re going to lay that out. Essentially, you should provide the reader with a high-level roadmap of your chapter to give them a taste of the journey that lies ahead.

Here’s an example of the layout visualised in a literature review introduction:

Your introduction should also outline your topic (including any tricky terminology or jargon) and provide an explanation of the scope of your literature review – in other words, what you  will   and  won’t   be covering (the delimitations ). This helps ringfence your review and achieve a clear focus . The clearer and narrower your focus, the deeper you can dive into the topic (which is typically where the magic lies). 

Depending on the nature of your project, you could also present your stance or point of view at this stage. In other words, after grappling with the literature you’ll have an opinion about what the trends and concerns are in the field as well as what’s lacking. The introduction section can then present these ideas so that it is clear to examiners that you’re aware of how your research connects with existing knowledge .

2: The Body Section

The body of your literature review is the centre of your work. This is where you’ll present, analyse, evaluate and synthesise the existing research. In other words, this is where you’re going to earn (or lose) the most marks. Therefore, it’s important to carefully think about how you will organise your discussion to present it in a clear way. 

The body of your literature review should do just as the description of this chapter suggests. It should “review” the literature – in other words, identify, analyse, and synthesise it. So, when thinking about structuring your literature review, you need to think about which structural approach will provide the best “review” for your specific type of research and objectives (we’ll get to this shortly).

There are (broadly speaking)  three options  for organising your literature review.

Option 1: Chronological (according to date)

Organising the literature chronologically is one of the simplest ways to structure your literature review. You start with what was published first and work your way through the literature until you reach the work published most recently. Pretty straightforward.

The benefit of this option is that it makes it easy to discuss the developments and debates in the field as they emerged over time. Organising your literature chronologically also allows you to highlight how specific articles or pieces of work might have changed the course of the field – in other words, which research has had the most impact . Therefore, this approach is very useful when your research is aimed at understanding how the topic has unfolded over time and is often used by scholars in the field of history. That said, this approach can be utilised by anyone that wants to explore change over time .

For example , if a student of politics is investigating how the understanding of democracy has evolved over time, they could use the chronological approach to provide a narrative that demonstrates how this understanding has changed through the ages.

Here are some questions you can ask yourself to help you structure your literature review chronologically.

• What is the earliest literature published relating to this topic?
• How has the field changed over time? Why?
• What are the most recent discoveries/theories?

In some ways, chronology plays a part whichever way you decide to structure your literature review, because you will always, to a certain extent, be analysing how the literature has developed. However, with the chronological approach, the emphasis is very firmly on how the discussion has evolved over time , as opposed to how all the literature links together (which we’ll discuss next ).

Option 2: Thematic (grouped by theme)

The thematic approach to structuring a literature review means organising your literature by theme or category – for example, by independent variables (i.e. factors that have an impact on a specific outcome).

As you’ve been collecting and synthesising literature , you’ll likely have started seeing some themes or patterns emerging. You can then use these themes or patterns as a structure for your body discussion. The thematic approach is the most common approach and is useful for structuring literature reviews in most fields.

For example, if you were researching which factors contributed towards people trusting an organisation, you might find themes such as consumers’ perceptions of an organisation’s competence, benevolence and integrity. Structuring your literature review thematically would mean structuring your literature review’s body section to discuss each of these themes, one section at a time.

Here are some questions to ask yourself when structuring your literature review by themes:

• Are there any patterns that have come to light in the literature?
• What are the central themes and categories used by the researchers?
• Do I have enough evidence of these themes?

PS – you can see an example of a thematically structured literature review in our literature review sample walkthrough video here.

Option 3: Methodological

The methodological option is a way of structuring your literature review by the research methodologies used . In other words, organising your discussion based on the angle from which each piece of research was approached – for example, qualitative , quantitative or mixed  methodologies.

Structuring your literature review by methodology can be useful if you are drawing research from a variety of disciplines and are critiquing different methodologies. The point of this approach is to question  how  existing research has been conducted, as opposed to  what  the conclusions and/or findings the research were.

For example, a sociologist might centre their research around critiquing specific fieldwork practices. Their literature review will then be a summary of the fieldwork methodologies used by different studies.

Here are some questions you can ask yourself when structuring your literature review according to methodology:

• Which methodologies have been utilised in this field?
• Which methodology is the most popular (and why)?
• What are the strengths and weaknesses of the various methodologies?
• How can the existing methodologies inform my own methodology?

3: The Conclusion Section

Once you’ve completed the body section of your literature review using one of the structural approaches we discussed above, you’ll need to “wrap up” your literature review and pull all the pieces together to set the direction for the rest of your dissertation or thesis.

The conclusion is where you’ll present the key findings of your literature review. In this section, you should emphasise the research that is especially important to your research questions and highlight the gaps that exist in the literature. Based on this, you need to make it clear what you will add to the literature – in other words, justify your own research by showing how it will help fill one or more of the gaps you just identified.

Last but not least, if it’s your intention to develop a conceptual framework for your dissertation or thesis, the conclusion section is a good place to present this.

Example: Thematically Structured Review

In the video below, we unpack a literature review chapter so that you can see an example of a thematically structure review in practice.

Let’s Recap

In this article, we’ve  discussed how to structure your literature review for maximum impact. Here’s a quick recap of what  you need to keep in mind when deciding on your literature review structure:

• Just like other chapters, your literature review needs a clear introduction , body and conclusion .
• The introduction section should provide an overview of what you will discuss in your literature review.
• The body section of your literature review can be organised by chronology , theme or methodology . The right structural approach depends on what you’re trying to achieve with your research.
• The conclusion section should draw together the key findings of your literature review and link them to your research questions.

If you’re ready to get started, be sure to download our free literature review template to fast-track your chapter outline.

Psst… there’s more!

This post is an extract from our bestselling short course, Literature Review Bootcamp . If you want to work smart, you don't want to miss this .

You Might Also Like:

27 Comments

Great work. This is exactly what I was looking for and helps a lot together with your previous post on literature review. One last thing is missing: a link to a great literature chapter of an journal article (maybe with comments of the different sections in this review chapter). Do you know any great literature review chapters?

I agree with you Marin… A great piece

I agree with Marin. This would be quite helpful if you annotate a nicely structured literature from previously published research articles.

Awesome article for my research.

I thank you immensely for this wonderful guide

It is indeed thought and supportive work for the futurist researcher and students

Very educative and good time to get guide. Thank you

Great work, very insightful. Thank you.

Thanks for this wonderful presentation. My question is that do I put all the variables into a single conceptual framework or each hypothesis will have it own conceptual framework?

Thank you very much, very helpful

This is very educative and precise . Thank you very much for dropping this kind of write up .

Pheeww, so damn helpful, thank you for this informative piece.

I’m doing a research project topic ; stool analysis for parasitic worm (enteric) worm, how do I structure it, thanks.

comprehensive explanation. Help us by pasting the URL of some good “literature review” for better understanding.

great piece. thanks for the awesome explanation. it is really worth sharing. I have a little question, if anyone can help me out, which of the options in the body of literature can be best fit if you are writing an architectural thesis that deals with design?

I am doing a research on nanofluids how can l structure it?

Beautifully clear.nThank you!

Lucid! Thankyou!

Brilliant work, well understood, many thanks

I like how this was so clear with simple language 😊😊 thank you so much 😊 for these information 😊

Insightful. I was struggling to come up with a sensible literature review but this has been really helpful. Thank you!

You have given thought-provoking information about the review of the literature.

Thank you. It has made my own research better and to impart your work to students I teach

I learnt a lot from this teaching. It’s a great piece.

I am doing research on EFL teacher motivation for his/her job. How Can I structure it? Is there any detailed template, additional to this?

You are so cool! I do not think I’ve read through something like this before. So nice to find somebody with some genuine thoughts on this issue. Seriously.. thank you for starting this up. This site is one thing that is required on the internet, someone with a little originality!

I’m asked to do conceptual, theoretical and empirical literature, and i just don’t know how to structure it

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• UNC Libraries
• HSL Academic Process
• Systematic Reviews
• Step 8: Write the Review

Systematic Reviews: Step 8: Write the Review

Created by health science librarians.

• Step 1: Complete Pre-Review Tasks
• Step 2: Develop a Protocol
• Step 3: Conduct Literature Searches
• Step 4: Manage Citations
• Step 5: Screen Citations
• Step 6: Assess Quality of Included Studies
• Step 7: Extract Data from Included Studies

About Step 8: Write the Review

Write your review, report your review with prisma, review sections, plain language summaries for systematic reviews, writing the review- webinars.

• Writing the Review FAQs

  Check our FAQ's

   Email us

   Call (919) 962-0800

   Make an appointment with a librarian

  Request a systematic or scoping review consultation

Search the FAQs

In Step 8, you will write an article or a paper about your systematic review.  It will likely have five sections: introduction, methods, results, discussion, and conclusion.  You will: 

• Review the reporting standards you will use, such as PRISMA. 
• Gather your completed data tables and PRISMA chart. 
• Write the Introduction to the topic and your study, Methods of your research, Results of your research, and Discussion of your results.
• Write an Abstract describing your study and a Conclusion summarizing your paper. 
• Cite the studies included in your systematic review and any other articles you may have used in your paper. 
• If you wish to publish your work, choose a target journal for your article.

The PRISMA Checklist will help you report the details of your systematic review. Your paper will also include a PRISMA chart that is an image of your research process. 

Click an item below to see how it applies to Step 8: Write the Review.

Reporting your review with PRISMA

To write your review, you will need the data from your PRISMA flow diagram .  Review the PRISMA checklist to see which items you should report in your methods section.

Managing your review with Covidence

When you screen in Covidence, it will record the numbers you need for your PRISMA flow diagram from duplicate removal through inclusion of studies.  You may need to add additional information, such as the number of references from each database, citations you find through grey literature or other searching methods, or the number of studies found in your previous work if you are updating a systematic review.

How a librarian can help with Step 8

A librarian can advise you on the process of organizing and writing up your systematic review, including: 

• Applying the PRISMA reporting templates and the level of detail to include for each element
• How to report a systematic review search strategy and your review methodology in the completed review
• How to use prior published reviews to guide you in organizing your manuscript 

Reporting standards & guidelines

Be sure to reference reporting standards when writing your review. This helps ensure that you communicate essential components of your methods, results, and conclusions. There are a number of tools that can be used to ensure compliance with reporting guidelines. A few review-writing resources are listed below.

• Cochrane Handbook - Chapter 15: Interpreting results and drawing conclusions
• JBI Manual for Evidence Synthesis - Chapter 12.3 The systematic review
• PRISMA 2020 (Preferred Reporting Items for Systematic Reviews and Meta-Analysis) The aim of the PRISMA Statement is to help authors improve the reporting of systematic reviews and meta-analyses.

Tools for writing your review

• RevMan (Cochrane Training)
• Methods Wizard (Systematic Review Accelerator) The Methods Wizard is part of the Systematic Review Accelerator created by Bond University and the Institute for Evidence-Based Healthcare.
• UNC HSL Systematic Review Manuscript Template Systematic review manuscript template(.doc) adapted from the PRISMA 2020 checklist. This document provides authors with template for writing about their systematic review. Each table contains a PRISMA checklist item that should be written about in that section, the matching PRISMA Item number, and a box where authors can indicate if an item has been completed. Once text has been added, delete any remaining instructions and the PRISMA checklist tables from the end of each section.
• The PRISMA 2020 statement: an updated guideline for reporting systematic reviews The PRISMA 2020 statement replaces the 2009 statement and includes new reporting guidance that reflects advances in methods to identify, select, appraise, and synthesise studies.
• PRISMA 2020 explanation and elaboration: updated guidance and exemplars for reporting systematic reviews This document is intended to enhance the use, understanding and dissemination of the PRISMA 2020 Statement. Through examples and explanations, the meaning and rationale for each checklist item are presented.

The PRISMA checklist

The Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) is a 27-item checklist used to improve transparency in systematic reviews. These items cover all aspects of the manuscript, including title, abstract, introduction, methods, results, discussion, and funding. The PRISMA checklist can be downloaded in PDF or Word files.

• PRISMA 2020 Checklists Download the 2020 PRISMA Checklists in Word or PDF formats or download the expanded checklist (PDF).

The PRISMA flow diagram

The PRISMA Flow Diagram visually depicts the flow of studies through each phase of the review process. The PRISMA Flow Diagram can be downloaded in Word files.

• PRISMA 2020 Flow Diagrams The flow diagram depicts the flow of information through the different phases of a systematic review. It maps out the number of records identified, included and excluded, and the reasons for exclusions. Different templates are available depending on the type of review (new or updated) and sources used to identify studies.

Documenting grey literature and/or hand searches

If you have also searched additional sources, such as professional organization websites, cited or citing references, etc., document your grey literature search using the flow diagram template version 1 PRISMA 2020 flow diagram for new systematic reviews which included searches of databases, registers and other sources or the version 2 PRISMA 2020 flow diagram for updated systematic reviews which included searches of databases, registers and other sources . 

Complete the boxes documenting your database searches,  Identification of studies via databases and registers, according to the PRISMA flow diagram instructions.  Complete the boxes documenting your grey literature and/or hand searches on the right side of the template, Identification of studies via other methods, using the steps below.

Need help completing the PRISMA flow diagram?

There are different PRISMA flow diagram templates for new and updated reviews, as well as different templates for reviews with and without grey literature searches. Be sure you download the correct template to match your review methods, then follow the steps below for each portion of the diagram you have available.

View the step-by-step explanation of the PRISMA flow diagram

Step 1: Preparation Download the flow diagram template version 1 PRISMA 2020 flow diagram for new systematic reviews which included searches of databases and registers only or the version 2 PRISMA 2020 flow diagram for updated systematic reviews which included searches of databases and registers only . 

View the step-by-step explanation of the grey literature & hand searching portion of the PRISMA flow diagram

Step 1: Preparation Download the flow diagram template version 1 PRISMA 2020 flow diagram for new systematic reviews which included searches of databases, registers and other sources or the version 2 PRISMA 2020 flow diagram for updated systematic reviews which included searches of databases, registers and other sources . 

View the step-by-step explanation of review update portion of the PRISMA flow diagram

Step 1: Preparation Download the flow diagram template version 2 PRISMA 2020 flow diagram for updated systematic reviews which included searches of databases and registers only or the version 2 PRISMA 2020 flow diagram for updated systematic reviews which included searches of databases, registers and other sources . 

For more information about updating your systematic review, see the box Updating Your Review? on the Step 3: Conduct Literature Searches page of the guide.

Sections of a Scientific Manuscript

Scientific articles often follow the IMRaD format: Introduction, Methods, Results, and Discussion.  You will also need a title and an abstract to summarize your research.

You can read more about scientific writing through the library guides below.

• Structure of Scholarly Articles & Peer Review • Explains the standard parts of a medical research article • Compares scholarly journals, professional trade journals, and magazines • Explains peer review and how to find peer reviewed articles and journals
• Writing in the Health Sciences (For Students and Instructors)
• Citing & Writing Tools & Guides Includes links to guides for popular citation managers such as EndNote, Sciwheel, Zotero; copyright basics; APA & AMA Style guides; Plagiarism & Citing Sources; Citing & Writing: How to Write Scientific Papers

Sections of a Systematic Review Manuscript

Systematic reviews follow the same structure as original research articles, but you will need to report on your search instead of on details like the participants or sampling. Sections of your manuscript are shown as bold headings in the PRISMA checklist.

Refer to the PRISMA checklist for more information.

Consider including a Plain Language Summary (PLS) when you publish your systematic review. Like an abstract, a PLS gives an overview of your study, but is specifically written and formatted to be easy for non-experts to understand. 

Tips for writing a PLS:

• Use clear headings e.g. "why did we do this study?"; "what did we do?"; "what did we find?"
• Use active voice e.g. "we searched for articles in 5 databases instead of "5 databases were searched"
• Consider need-to-know vs. nice-to-know: what is most important for readers to understand about your study? Be sure to provide the most important points without misrepresenting your study or misleading the reader. 
• Keep it short: Many journals recommend keeping your plain language summary less than 250 words. 
• Check journal guidelines: Your journal may have specific guidelines about the format of your plain language summary and when you can publish it. Look at journal guidelines before submitting your article. 

Learn more about Plain Language Summaries: 

• Rosenberg, A., Baróniková, S., & Feighery, L. (2021). Open Pharma recommendations for plain language summaries of peer-reviewed medical journal publications. Current Medical Research and Opinion, 37(11), 2015–2016.  https://doi.org/10.1080/03007995.2021.1971185
• Lobban, D., Gardner, J., & Matheis, R. (2021). Plain language summaries of publications of company-sponsored medical research: what key questions do we need to address? Current Medical Research and Opinion, 1–12. https://doi.org/10.1080/03007995.2021.1997221
• Cochrane Community. (2022, March 21). Updated template and guidance for writing Plain Language Summaries in Cochrane Reviews now available. https://community.cochrane.org/news/updated-template-and-guidance-writing-plain-language-summaries-cochrane-reviews-now-available
• You can also look at our Health Literacy LibGuide:  https://guides.lib.unc.edu/healthliteracy 

How to Approach Writing a Background Section

What Makes a Good Discussion Section

Writing Up Risk of Bias

Developing Your Implications for Research Section

• << Previous: Step 7: Extract Data from Included Studies
• Next: FAQs >>
• Last Updated: May 14, 2024 12:50 PM
• URL: https://guides.lib.unc.edu/systematic-reviews

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• Steps in Conducting a Literature Review

What is a literature review?

A literature review is an integrated analysis -- not just a summary-- of scholarly writings and other relevant evidence related directly to your research question.  That is, it represents a synthesis of the evidence that provides background information on your topic and shows a association between the evidence and your research question.

A literature review may be a stand alone work or the introduction to a larger research paper, depending on the assignment.  Rely heavily on the guidelines your instructor has given you.

Why is it important?

A literature review is important because it:

• Explains the background of research on a topic.
• Demonstrates why a topic is significant to a subject area.
• Discovers relationships between research studies/ideas.
• Identifies major themes, concepts, and researchers on a topic.
• Identifies critical gaps and points of disagreement.
• Discusses further research questions that logically come out of the previous studies.

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1. Choose a topic. Define your research question.

Your literature review should be guided by your central research question.  The literature represents background and research developments related to a specific research question, interpreted and analyzed by you in a synthesized way.

• Make sure your research question is not too broad or too narrow.  Is it manageable?
• Begin writing down terms that are related to your question. These will be useful for searches later.
• If you have the opportunity, discuss your topic with your professor and your class mates.

2. Decide on the scope of your review

How many studies do you need to look at? How comprehensive should it be? How many years should it cover? 

• This may depend on your assignment.  How many sources does the assignment require?

3. Select the databases you will use to conduct your searches.

Make a list of the databases you will search. 

Where to find databases:

• use the tabs on this guide
• Find other databases in the Nursing Information Resources web page
• More on the Medical Library web page
• ... and more on the Yale University Library web page

4. Conduct your searches to find the evidence. Keep track of your searches.

• Use the key words in your question, as well as synonyms for those words, as terms in your search. Use the database tutorials for help.
• Save the searches in the databases. This saves time when you want to redo, or modify, the searches. It is also helpful to use as a guide is the searches are not finding any useful results.
• Review the abstracts of research studies carefully. This will save you time.
• Use the bibliographies and references of research studies you find to locate others.
• Check with your professor, or a subject expert in the field, if you are missing any key works in the field.
• Ask your librarian for help at any time.
• Use a citation manager, such as EndNote as the repository for your citations. See the EndNote tutorials for help.

Review the literature

Some questions to help you analyze the research:

• What was the research question of the study you are reviewing? What were the authors trying to discover?
• Was the research funded by a source that could influence the findings?
• What were the research methodologies? Analyze its literature review, the samples and variables used, the results, and the conclusions.
• Does the research seem to be complete? Could it have been conducted more soundly? What further questions does it raise?
• If there are conflicting studies, why do you think that is?
• How are the authors viewed in the field? Has this study been cited? If so, how has it been analyzed?

Tips: 

• Review the abstracts carefully.  
• Keep careful notes so that you may track your thought processes during the research process.
• Create a matrix of the studies for easy analysis, and synthesis, across all of the studies.
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• PRISMA flow diagram generator

Resource link

• PRISMA flow diagram templates

This tool, developed by PRISMA, can be used to develop a PRISMA flow diagram in order to report on systematic reviews.

The flow diagram depicts the flow of information through the different phases of a systematic review. It maps out the number of records identified, included and excluded, and the reasons for exclusions.

The aim of the PRISMA Statement is to help authors report a wide array of systematic reviews to assess the benefits and harms of a health care intervention. PRISMA focuses on ways in which authors can ensure the transparent and complete reporting of systematic reviews and meta-analyses.

We have adopted the definitions of systematic review and meta-analysis used by the Cochrane Collaboration [9]. A systematic review is a review of a clearly formulated question that uses systematic and explicit methods to identify, select, and critically appraise relevant research, and to collect and analyse data from the studies that are included in the review. Statistical methods (meta-analysis) may or may not be used to analyse and summarise the results of the included studies. Meta-analysis refers to the use of statistical techniques in a systematic review to integrate the results of included studies.

PRISMA (n.d.). PRISMA Flow Diagram Generator . Retrieved from: https://estech.shinyapps.io/prisma_flowdiagram/

PRISMA (n.d.). PRISMA Flow Diagram Generator . Retrieved from: http://prisma-statement.org/PRISMAStatement/

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• Open access
• Published: 19 April 2021

How to properly use the PRISMA Statement

• Rafael Sarkis-Onofre 1 ,
• Ferrán Catalá-López 2 , 3 ,
• Edoardo Aromataris 4 &
• Craig Lockwood 4  

Systematic Reviews volume  10 , Article number:  117 ( 2021 ) Cite this article

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It has been more than a decade since the original publication of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) Statement [ 1 ], and it has become one of the most cited reporting guidelines in biomedical literature [ 2 , 3 ]. Since its publication, multiple extensions of the PRISMA Statement have been published concomitant with the advancement of knowledge synthesis methods [ 4 , 5 , 6 , 7 ]. The PRISMA2020 statement, an updated version has recently been published [ 8 ], and other extensions are currently in development [ 9 ].

The number of systematic reviews (SRs) has increased substantially over the past 20 years [ 10 , 11 , 12 ]. However, many SRs continue to be poorly conducted and reported [ 10 , 11 ], and it is still common to see articles that use the PRISMA Statement and other reporting guidelines inappropriately, as was highlighted recently [ 13 ].

The PRISMA Statement and its extensions are an evidence-based, minimum set of recommendations designed primarily to encourage transparent and complete reporting of SRs. This growing set of guidelines have been developed to aid authors with appropriate reporting of different knowledge synthesis methods (such as SRs, scoping reviews, and review protocols) and to ensure that all aspects of this type of research are accurately and transparently reported. In other words, the PRISMA Statement is a road map to help authors best describe what was done, what was found, and in the case of a review protocol, what are they are planning to do.

Despite this clear and well-articulated intention [ 2 , 3 , 4 , 5 ], it is common for Systematic Reviews to receive manuscripts detailing the inappropriate use of the PRISMA Statement and its extensions. Most frequently, improper use appears with authors attempting to use the PRISMA statement as a methodological guideline for the design and conduct reviews, or identifying the PRISMA statement as a tool to assess the methodological quality of reviews, as seen in the following examples:

“This scoping review will be conducted according to the Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) Statement.”

“This protocol was designed based on the Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols (PRISMA-P) Statement.”

“The methodological quality of the included systematic reviews will be assessed with the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) Statement.”

Some organizations (such as Cochrane and JBI) have developed methodological guidelines that can help authors to design or conduct diverse types of knowledge synthesis rigorously [ 14 , 15 ]. While the PRISMA statement is presented to predominantly guide reporting of a systematic review of interventions with meta-analyses, its detailed criteria can readily be applied to the majority of review types [ 13 ]. Differences between the role of the PRISMA Statement to guide reporting versus guidelines detailing methodological conduct is readily illustrated with the following example: the PRISMA Statement recommends that authors report their complete search strategies for all databases, registers, and websites (including any filters and limits used), but it does not include recommendations for designing and conducting literature searches [ 8 ]. If authors are interested in understanding how to create search strategies or which databases to include, they should refer to the methodological guidelines [ 12 , 13 ]. Thus, the following examples can illustrate the appropriate use of the PRISMA Statement in research reporting:

“The reporting of this systematic review was guided by the standards of the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) Statement.”

“This scoping review was reported according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR).”

“The protocol is being reported in accordance with the Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols (PRISMA-P) Statement.”

Systematic Reviews supports the complete and transparent reporting of research. The Editors require the submission of a populated checklist from the relevant reporting guidelines, including the PRISMA checklist or the most appropriate PRISMA extension. Using the PRISMA statement and its extensions to write protocols or the completed review report, and completing the PRISMA checklists are likely to let reviewers and readers know what authors did and found, but also to optimize the quality of reporting and make the peer review process more efficient.

Transparent and complete reporting is an essential component of “good research”; it allows readers to judge key issues regarding the conduct of research and its trustworthiness and is also critical to establish a study’s replicability.

With the release of a major update to PRISMA in 2021, the appropriate use of the updated PRISMA Statement (and its extensions as those updates progress) will be an essential requirement for review based submissions, and we encourage authors, peer reviewers, and readers of Systematic Reviews to use and disseminate that initiative.

Availability of data and materials

We do not have any additional data or materials to share.

Abbreviations

Preferred Reporting Items for Systematic Reviews and Meta-Analyses

Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews

Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols

Systematic reviews

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Hutton B, Salanti G, Caldwell DM, Chaimani A, Schmid CH, Cameron C, et al. The PRISMA extension statement for reporting of systematic reviews incorporating network meta-analyses of health care interventions: checklist and explanations. Ann Intern Med. 2015;162(11):777–84. https://doi.org/10.7326/M14-2385 .

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EQUATOR Network: Reporting guidelines under development for systematic reviews. https://www.equator-network.org/library/reporting-guidelines-under-development/reporting-guidelines-under-development-for-systematic-reviews/ . Accessed 11 Feb 2021.

Page MJ, Shamseer L, Altman DG, Tetzlaff J, Sampson M, Tricco AC, et al. Epidemiology and Reporting Characteristics of Systematic Reviews of Biomedical Research: A Cross-Sectional Study. Plos Med. 2016;13(5):e1002028. https://doi.org/10.1371/journal.pmed.1002028 .

Ioannidis JP. The Mass Production of Redundant, Misleading, and Conflicted Systematic Reviews and Meta-analyses. Milbank Q. 2016;94(3):485–514. https://doi.org/10.1111/1468-0009.12210 .

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Higgins JPT, Thomas J, Chandler J, Cumpston M, Li T, Page MJ, Welch VA (editors). Cochrane Handbook for Systematic Reviews of Interventions. 2nd Edition ed. Chichester: Wiley; 2019.

Aromataris E, Munn Z (Editors). JBI Manual for Evidence Synthesis. ed. Adelaide: JBI; 2020.

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Acknowledgements

RSO is funded in part by Meridional Foundation. FCL is funded in part by the Institute of Health Carlos III/CIBERSAM.

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Graduate Program in Dentistry, Meridional Faculty, IMED, Passo Fundo, Brazil

Rafael Sarkis-Onofre

Department of Health Planning and Economics, National School of Public Health, Institute of Health Carlos III, Madrid, Spain

Ferrán Catalá-López

Department of Medicine, University of Valencia/INCLIVA Health Research Institute and CIBERSAM, Valencia, Spain

JBI, Faculty of Health and Medical Sciences, The University of Adelaide, Adelaide, Australia

Edoardo Aromataris & Craig Lockwood

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RSO drafted the initial version. FCL, EA, and CL made substantial additions to the first and subsequent drafts. All authors read and approved the final manuscript.

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Correspondence to Rafael Sarkis-Onofre .

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CL is Editor-in-Chief of Systematic Reviews, FCL is Protocol Editor of Systematic Reviews, and RSO is Associate Editor of Systematic Reviews.

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Sarkis-Onofre, R., Catalá-López, F., Aromataris, E. et al. How to properly use the PRISMA Statement. Syst Rev 10 , 117 (2021). https://doi.org/10.1186/s13643-021-01671-z

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Evidence synthesis & literature reviews education, what do you want to learn about, selected training, review types, evidence synthesis process, selected protocols, guidelines, & tools.

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This module series helps users gain a more in-depth understanding of the process of conducting a systematic review. Make sure you are connected to the VPN before registering for a free account.

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Title: "What type of Review Could You Write"

Top of chart begins Q: "How big is your team?"

• If "Yes" to robust methodology, then "Rapid Review"
• If "No to robust methodology, then "Narrative Review"
• If "Yes", then "Systematic Review and Meta-analysis"
• If "Open", then "Scoping Review"

Build your evidence synthesis team [preparation stage]

Review reporting guidelines, best practice handbooks, and training modules [preparation stage]

Formulate question and decide on review type [preparation stage]

Search for previous published literature and protocols [preparation stage]

Develop and register a protocol [write-up stage]

Develop and test search strategies [preparation stage]

Peer review of search strategies [preparation stage]

Execute search [retrieval stage]

De-duplicate results [retrieval stage]

Screen title and abstracts [screening stage]

Retrieve full-text articles [retrieval stage]

Screen articles in full-text [screening stage]

Search for grey literature [retrieval stage]

Quality assessment and data extraction [synthesis stage]

Citation chasing [retrieval stage]

Update database searches [retrieval stage]

Synthesize data [synthesis stage]

Manuscript development [write-up stage]

View this process as a graphic

Protocols & Reporting Guidelines

• PRISMA  (Preferred Reporting Items for Systematic Reviews and Meta-Analyses)
• MOOSE  (Meta-analyisis of Observational Studies in Epidemiology) 
• ENTREQ  (Enhancing Transparency in Reporting the Synthesis of Qualitative Research)

Protocol Registries

• PROSPERO  (International Prospective Register of Systematic Reviews)
• Open Science Framework: Registries

Quality Assessment Instruments

• CATevaluation : a listing of Critical Appraisal Tools assessed for validity and/or reliability
• GRADE: Grading of Recommendations Assessment, Development and Evaluation
• Critical Appraisal Skills Program (CASP) Checklist
• JBI Critical Appraisal Tools
• Risk of bias tools in systematic reviews of health interventions: an analysis of PROSPERO-registered protocols  (article)
• Critical appraisal of nonrandomized studies: a review of recommended and commonly used tools  (article)

Best Practices

• Cochrane Handbook for Systematic Reviews of Interventions
• CRDs Guidance for Undertaking Reviews in Health Care
• JBI Best Practices  (Joanna Briggs Institute)
• MECIR  (Methodological Expectations for Cochrane Intervention Reviews)
• Publications on systematic review / evidence synthesis methodology (EPPI-Centre)
• Methods Guide for Effectiveness and Comparative Effectiveness Reviews (Agency for Healthcare Research and Quality)
• Yale MeSH Analyzer  - helps identify the problems in your search strategy
• Covidence  - manage bibliographic data, PDFs, forms for risk of bias, and data extraction
• EndNote  - citation management software
• What Review Is Right For You? Interactive Edition  - guidance for conducting and reporting evidence synthesis
• An Introduction to Systematic Reviews  edited by David Gough, Sandy Oliver, James Thomas  
• Systematic Reviews and Meta-Analysis  by Jacqueline Corcoran; Vijayan Pillai; Julia H. Littell
• The Handbook of Research Synthesis and Meta-Analysis  edited by Harris Cooper, Larry V. Hedges, Jeffrey C. Valentine
• Searching the Grey Literature: A handbook for Searching Reports, Working Papers, and other Unpublished Research  by Sarah Bonato

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What is a Literature Review? How to Write It (with Examples)

A literature review is a critical analysis and synthesis of existing research on a particular topic. It provides an overview of the current state of knowledge, identifies gaps, and highlights key findings in the literature. 1 The purpose of a literature review is to situate your own research within the context of existing scholarship, demonstrating your understanding of the topic and showing how your work contributes to the ongoing conversation in the field. Learning how to write a literature review is a critical tool for successful research. Your ability to summarize and synthesize prior research pertaining to a certain topic demonstrates your grasp on the topic of study, and assists in the learning process. 

Table of Contents

• What is the purpose of literature review? 
• a. Habitat Loss and Species Extinction: 
• b. Range Shifts and Phenological Changes: 
• c. Ocean Acidification and Coral Reefs: 
• d. Adaptive Strategies and Conservation Efforts: 

How to write a good literature review 

• Choose a Topic and Define the Research Question: 
• Decide on the Scope of Your Review: 
• Select Databases for Searches: 
• Conduct Searches and Keep Track: 
• Review the Literature: 
• Organize and Write Your Literature Review: 
• How to write a literature review faster with Paperpal? 
• Frequently asked questions 

What is a literature review?

A well-conducted literature review demonstrates the researcher’s familiarity with the existing literature, establishes the context for their own research, and contributes to scholarly conversations on the topic. One of the purposes of a literature review is also to help researchers avoid duplicating previous work and ensure that their research is informed by and builds upon the existing body of knowledge.

What is the purpose of literature review?

A literature review serves several important purposes within academic and research contexts. Here are some key objectives and functions of a literature review: 2  

1. Contextualizing the Research Problem: The literature review provides a background and context for the research problem under investigation. It helps to situate the study within the existing body of knowledge. 

2. Identifying Gaps in Knowledge: By identifying gaps, contradictions, or areas requiring further research, the researcher can shape the research question and justify the significance of the study. This is crucial for ensuring that the new research contributes something novel to the field. 

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3. Understanding Theoretical and Conceptual Frameworks: Literature reviews help researchers gain an understanding of the theoretical and conceptual frameworks used in previous studies. This aids in the development of a theoretical framework for the current research. 

4. Providing Methodological Insights: Another purpose of literature reviews is that it allows researchers to learn about the methodologies employed in previous studies. This can help in choosing appropriate research methods for the current study and avoiding pitfalls that others may have encountered. 

5. Establishing Credibility: A well-conducted literature review demonstrates the researcher’s familiarity with existing scholarship, establishing their credibility and expertise in the field. It also helps in building a solid foundation for the new research. 

6. Informing Hypotheses or Research Questions: The literature review guides the formulation of hypotheses or research questions by highlighting relevant findings and areas of uncertainty in existing literature. 

Literature review example

Let’s delve deeper with a literature review example: Let’s say your literature review is about the impact of climate change on biodiversity. You might format your literature review into sections such as the effects of climate change on habitat loss and species extinction, phenological changes, and marine biodiversity. Each section would then summarize and analyze relevant studies in those areas, highlighting key findings and identifying gaps in the research. The review would conclude by emphasizing the need for further research on specific aspects of the relationship between climate change and biodiversity. The following literature review template provides a glimpse into the recommended literature review structure and content, demonstrating how research findings are organized around specific themes within a broader topic. 

Literature Review on Climate Change Impacts on Biodiversity:

Climate change is a global phenomenon with far-reaching consequences, including significant impacts on biodiversity. This literature review synthesizes key findings from various studies: 

a. Habitat Loss and Species Extinction:

Climate change-induced alterations in temperature and precipitation patterns contribute to habitat loss, affecting numerous species (Thomas et al., 2004). The review discusses how these changes increase the risk of extinction, particularly for species with specific habitat requirements. 

b. Range Shifts and Phenological Changes:

Observations of range shifts and changes in the timing of biological events (phenology) are documented in response to changing climatic conditions (Parmesan & Yohe, 2003). These shifts affect ecosystems and may lead to mismatches between species and their resources. 

c. Ocean Acidification and Coral Reefs:

The review explores the impact of climate change on marine biodiversity, emphasizing ocean acidification’s threat to coral reefs (Hoegh-Guldberg et al., 2007). Changes in pH levels negatively affect coral calcification, disrupting the delicate balance of marine ecosystems. 

d. Adaptive Strategies and Conservation Efforts:

Recognizing the urgency of the situation, the literature review discusses various adaptive strategies adopted by species and conservation efforts aimed at mitigating the impacts of climate change on biodiversity (Hannah et al., 2007). It emphasizes the importance of interdisciplinary approaches for effective conservation planning. 

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Writing a literature review involves summarizing and synthesizing existing research on a particular topic. A good literature review format should include the following elements. 

Introduction: The introduction sets the stage for your literature review, providing context and introducing the main focus of your review. 

• Opening Statement: Begin with a general statement about the broader topic and its significance in the field. 
• Scope and Purpose: Clearly define the scope of your literature review. Explain the specific research question or objective you aim to address. 
• Organizational Framework: Briefly outline the structure of your literature review, indicating how you will categorize and discuss the existing research. 
• Significance of the Study: Highlight why your literature review is important and how it contributes to the understanding of the chosen topic. 
• Thesis Statement: Conclude the introduction with a concise thesis statement that outlines the main argument or perspective you will develop in the body of the literature review. 

Body: The body of the literature review is where you provide a comprehensive analysis of existing literature, grouping studies based on themes, methodologies, or other relevant criteria. 

• Organize by Theme or Concept: Group studies that share common themes, concepts, or methodologies. Discuss each theme or concept in detail, summarizing key findings and identifying gaps or areas of disagreement. 
• Critical Analysis: Evaluate the strengths and weaknesses of each study. Discuss the methodologies used, the quality of evidence, and the overall contribution of each work to the understanding of the topic. 
• Synthesis of Findings: Synthesize the information from different studies to highlight trends, patterns, or areas of consensus in the literature. 
• Identification of Gaps: Discuss any gaps or limitations in the existing research and explain how your review contributes to filling these gaps. 
• Transition between Sections: Provide smooth transitions between different themes or concepts to maintain the flow of your literature review. 

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Conclusion: The conclusion of your literature review should summarize the main findings, highlight the contributions of the review, and suggest avenues for future research. 

• Summary of Key Findings: Recap the main findings from the literature and restate how they contribute to your research question or objective. 
• Contributions to the Field: Discuss the overall contribution of your literature review to the existing knowledge in the field. 
• Implications and Applications: Explore the practical implications of the findings and suggest how they might impact future research or practice. 
• Recommendations for Future Research: Identify areas that require further investigation and propose potential directions for future research in the field. 
• Final Thoughts: Conclude with a final reflection on the importance of your literature review and its relevance to the broader academic community. 

Conducting a literature review

Conducting a literature review is an essential step in research that involves reviewing and analyzing existing literature on a specific topic. It’s important to know how to do a literature review effectively, so here are the steps to follow: 1  

Choose a Topic and Define the Research Question:

• Select a topic that is relevant to your field of study. 
• Clearly define your research question or objective. Determine what specific aspect of the topic do you want to explore? 

Decide on the Scope of Your Review:

• Determine the timeframe for your literature review. Are you focusing on recent developments, or do you want a historical overview? 
• Consider the geographical scope. Is your review global, or are you focusing on a specific region? 
• Define the inclusion and exclusion criteria. What types of sources will you include? Are there specific types of studies or publications you will exclude? 

Select Databases for Searches:

• Identify relevant databases for your field. Examples include PubMed, IEEE Xplore, Scopus, Web of Science, and Google Scholar. 
• Consider searching in library catalogs, institutional repositories, and specialized databases related to your topic. 

Conduct Searches and Keep Track:

• Develop a systematic search strategy using keywords, Boolean operators (AND, OR, NOT), and other search techniques. 
• Record and document your search strategy for transparency and replicability. 
• Keep track of the articles, including publication details, abstracts, and links. Use citation management tools like EndNote, Zotero, or Mendeley to organize your references. 

Review the Literature:

• Evaluate the relevance and quality of each source. Consider the methodology, sample size, and results of studies. 
• Organize the literature by themes or key concepts. Identify patterns, trends, and gaps in the existing research. 
• Summarize key findings and arguments from each source. Compare and contrast different perspectives. 
• Identify areas where there is a consensus in the literature and where there are conflicting opinions. 
• Provide critical analysis and synthesis of the literature. What are the strengths and weaknesses of existing research? 

Organize and Write Your Literature Review:

• Literature review outline should be based on themes, chronological order, or methodological approaches. 
• Write a clear and coherent narrative that synthesizes the information gathered. 
• Use proper citations for each source and ensure consistency in your citation style (APA, MLA, Chicago, etc.). 
• Conclude your literature review by summarizing key findings, identifying gaps, and suggesting areas for future research. 

Whether you’re exploring a new research field or finding new angles to develop an existing topic, sifting through hundreds of papers can take more time than you have to spare. But what if you could find science-backed insights with verified citations in seconds? That’s the power of Paperpal’s new Research feature!  

How to write a literature review faster with Paperpal?

Paperpal, an AI writing assistant, integrates powerful academic search capabilities within its writing platform. With the Research feature, you get 100% factual insights, with citations backed by 250M+ verified research articles, directly within your writing interface with the option to save relevant references in your Citation Library. By eliminating the need to switch tabs to find answers to all your research questions, Paperpal saves time and helps you stay focused on your writing.   

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• Cite with Confidence: Paperpal makes it easy to incorporate relevant citations and references into your writing, ensuring your arguments are well-supported by credible sources. This translates to a polished, well-researched literature review. 

The literature review sample and detailed advice on writing and conducting a review will help you produce a well-structured report. But remember that a good literature review is an ongoing process, and it may be necessary to revisit and update it as your research progresses. By combining effortless research with an easy citation process, Paperpal Research streamlines the literature review process and empowers you to write faster and with more confidence. Try Paperpal Research now and see for yourself.  

Frequently asked questions

A literature review is a critical and comprehensive analysis of existing literature (published and unpublished works) on a specific topic or research question and provides a synthesis of the current state of knowledge in a particular field. A well-conducted literature review is crucial for researchers to build upon existing knowledge, avoid duplication of efforts, and contribute to the advancement of their field. It also helps researchers situate their work within a broader context and facilitates the development of a sound theoretical and conceptual framework for their studies.

Literature review is a crucial component of research writing, providing a solid background for a research paper’s investigation. The aim is to keep professionals up to date by providing an understanding of ongoing developments within a specific field, including research methods, and experimental techniques used in that field, and present that knowledge in the form of a written report. Also, the depth and breadth of the literature review emphasizes the credibility of the scholar in his or her field.  

Before writing a literature review, it’s essential to undertake several preparatory steps to ensure that your review is well-researched, organized, and focused. This includes choosing a topic of general interest to you and doing exploratory research on that topic, writing an annotated bibliography, and noting major points, especially those that relate to the position you have taken on the topic. 

Literature reviews and academic research papers are essential components of scholarly work but serve different purposes within the academic realm. 3 A literature review aims to provide a foundation for understanding the current state of research on a particular topic, identify gaps or controversies, and lay the groundwork for future research. Therefore, it draws heavily from existing academic sources, including books, journal articles, and other scholarly publications. In contrast, an academic research paper aims to present new knowledge, contribute to the academic discourse, and advance the understanding of a specific research question. Therefore, it involves a mix of existing literature (in the introduction and literature review sections) and original data or findings obtained through research methods. 

Literature reviews are essential components of academic and research papers, and various strategies can be employed to conduct them effectively. If you want to know how to write a literature review for a research paper, here are four common approaches that are often used by researchers.  Chronological Review: This strategy involves organizing the literature based on the chronological order of publication. It helps to trace the development of a topic over time, showing how ideas, theories, and research have evolved.  Thematic Review: Thematic reviews focus on identifying and analyzing themes or topics that cut across different studies. Instead of organizing the literature chronologically, it is grouped by key themes or concepts, allowing for a comprehensive exploration of various aspects of the topic.  Methodological Review: This strategy involves organizing the literature based on the research methods employed in different studies. It helps to highlight the strengths and weaknesses of various methodologies and allows the reader to evaluate the reliability and validity of the research findings.  Theoretical Review: A theoretical review examines the literature based on the theoretical frameworks used in different studies. This approach helps to identify the key theories that have been applied to the topic and assess their contributions to the understanding of the subject.  It’s important to note that these strategies are not mutually exclusive, and a literature review may combine elements of more than one approach. The choice of strategy depends on the research question, the nature of the literature available, and the goals of the review. Additionally, other strategies, such as integrative reviews or systematic reviews, may be employed depending on the specific requirements of the research.

The literature review format can vary depending on the specific publication guidelines. However, there are some common elements and structures that are often followed. Here is a general guideline for the format of a literature review:  Introduction:   Provide an overview of the topic.  Define the scope and purpose of the literature review.  State the research question or objective.  Body:   Organize the literature by themes, concepts, or chronology.  Critically analyze and evaluate each source.  Discuss the strengths and weaknesses of the studies.  Highlight any methodological limitations or biases.  Identify patterns, connections, or contradictions in the existing research.  Conclusion:   Summarize the key points discussed in the literature review.  Highlight the research gap.  Address the research question or objective stated in the introduction.  Highlight the contributions of the review and suggest directions for future research.

Both annotated bibliographies and literature reviews involve the examination of scholarly sources. While annotated bibliographies focus on individual sources with brief annotations, literature reviews provide a more in-depth, integrated, and comprehensive analysis of existing literature on a specific topic. The key differences are as follows: 

References 

• Denney, A. S., & Tewksbury, R. (2013). How to write a literature review.  Journal of criminal justice education ,  24 (2), 218-234. 
• Pan, M. L. (2016).  Preparing literature reviews: Qualitative and quantitative approaches . Taylor & Francis. 
• Cantero, C. (2019). How to write a literature review.  San José State University Writing Center . 

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The PRISMA 2020 statement: an updated guideline for reporting systematic reviews

PRISMA 2020 explanation and elaboration: updated guidance and exemplars for reporting systematic reviews

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• Peer review
• Matthew J Page , senior research fellow 1 ,
• Joanne E McKenzie , associate professor 1 ,
• Patrick M Bossuyt , professor 2 ,
• Isabelle Boutron , professor 3 ,
• Tammy C Hoffmann , professor 4 ,
• Cynthia D Mulrow , professor 5 ,
• Larissa Shamseer , doctoral student 6 ,
• Jennifer M Tetzlaff , research product specialist 7 ,
• Elie A Akl , professor 8 ,
• Sue E Brennan , senior research fellow 1 ,
• Roger Chou , professor 9 ,
• Julie Glanville , associate director 10 ,
• Jeremy M Grimshaw , professor 11 ,
• Asbjørn Hróbjartsson , professor 12 ,
• Manoj M Lalu , associate scientist and assistant professor 13 ,
• Tianjing Li , associate professor 14 ,
• Elizabeth W Loder , professor 15 ,
• Evan Mayo-Wilson , associate professor 16 ,
• Steve McDonald , senior research fellow 1 ,
• Luke A McGuinness , research associate 17 ,
• Lesley A Stewart , professor and director 18 ,
• James Thomas , professor 19 ,
• Andrea C Tricco , scientist and associate professor 20 ,
• Vivian A Welch , associate professor 21 ,
• Penny Whiting , associate professor 17 ,
• David Moher , director and professor 22
• 1 School of Public Health and Preventive Medicine, Monash University, Melbourne, Australia
• 2 Department of Clinical Epidemiology, Biostatistics and Bioinformatics, Amsterdam University Medical Centres, University of Amsterdam, Amsterdam, Netherlands
• 3 Université de Paris, Centre of Epidemiology and Statistics (CRESS), Inserm, F 75004 Paris, France
• 4 Institute for Evidence-Based Healthcare, Faculty of Health Sciences and Medicine, Bond University, Gold Coast, Australia
• 5 University of Texas Health Science Center at San Antonio, San Antonio, Texas, USA; Annals of Internal Medicine
• 6 Knowledge Translation Program, Li Ka Shing Knowledge Institute, Toronto, Canada; School of Epidemiology and Public Health, Faculty of Medicine, University of Ottawa, Ottawa, Canada
• 7 Evidence Partners, Ottawa, Canada
• 8 Clinical Research Institute, American University of Beirut, Beirut, Lebanon; Department of Health Research Methods, Evidence, and Impact, McMaster University, Hamilton, Ontario, Canada
• 9 Department of Medical Informatics and Clinical Epidemiology, Oregon Health & Science University, Portland, Oregon, USA
• 10 York Health Economics Consortium (YHEC Ltd), University of York, York, UK
• 11 Clinical Epidemiology Program, Ottawa Hospital Research Institute, Ottawa, Canada; School of Epidemiology and Public Health, University of Ottawa, Ottawa, Canada; Department of Medicine, University of Ottawa, Ottawa, Canada
• 12 Centre for Evidence-Based Medicine Odense (CEBMO) and Cochrane Denmark, Department of Clinical Research, University of Southern Denmark, Odense, Denmark; Open Patient data Exploratory Network (OPEN), Odense University Hospital, Odense, Denmark
• 13 Department of Anesthesiology and Pain Medicine, The Ottawa Hospital, Ottawa, Canada; Clinical Epidemiology Program, Blueprint Translational Research Group, Ottawa Hospital Research Institute, Ottawa, Canada; Regenerative Medicine Program, Ottawa Hospital Research Institute, Ottawa, Canada
• 14 Department of Ophthalmology, School of Medicine, University of Colorado Denver, Denver, Colorado, United States; Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, USA
• 15 Division of Headache, Department of Neurology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA; Head of Research, The BMJ , London, UK
• 16 Department of Epidemiology and Biostatistics, Indiana University School of Public Health-Bloomington, Bloomington, Indiana, USA
• 17 Population Health Sciences, Bristol Medical School, University of Bristol, Bristol, UK
• 18 Centre for Reviews and Dissemination, University of York, York, UK
• 19 EPPI-Centre, UCL Social Research Institute, University College London, London, UK
• 20 Li Ka Shing Knowledge Institute of St. Michael's Hospital, Unity Health Toronto, Toronto, Canada; Epidemiology Division of the Dalla Lana School of Public Health and the Institute of Health Management, Policy, and Evaluation, University of Toronto, Toronto, Canada; Queen's Collaboration for Health Care Quality Joanna Briggs Institute Centre of Excellence, Queen's University, Kingston, Canada
• 21 Methods Centre, Bruyère Research Institute, Ottawa, Ontario, Canada; School of Epidemiology and Public Health, Faculty of Medicine, University of Ottawa, Ottawa, Canada
• 22 Centre for Journalology, Clinical Epidemiology Program, Ottawa Hospital Research Institute, Ottawa, Canada; School of Epidemiology and Public Health, Faculty of Medicine, University of Ottawa, Ottawa, Canada
• Correspondence to: M J Page matthew.page{at}monash.edu
• Accepted 4 January 2021

The Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) statement, published in 2009, was designed to help systematic reviewers transparently report why the review was done, what the authors did, and what they found. Over the past decade, advances in systematic review methodology and terminology have necessitated an update to the guideline. The PRISMA 2020 statement replaces the 2009 statement and includes new reporting guidance that reflects advances in methods to identify, select, appraise, and synthesise studies. The structure and presentation of the items have been modified to facilitate implementation. In this article, we present the PRISMA 2020 27-item checklist, an expanded checklist that details reporting recommendations for each item, the PRISMA 2020 abstract checklist, and the revised flow diagrams for original and updated reviews.

Systematic reviews serve many critical roles. They can provide syntheses of the state of knowledge in a field, from which future research priorities can be identified; they can address questions that otherwise could not be answered by individual studies; they can identify problems in primary research that should be rectified in future studies; and they can generate or evaluate theories about how or why phenomena occur. Systematic reviews therefore generate various types of knowledge for different users of reviews (such as patients, healthcare providers, researchers, and policy makers). 1 2 To ensure a systematic review is valuable to users, authors should prepare a transparent, complete, and accurate account of why the review was done, what they did (such as how studies were identified and selected) and what they found (such as characteristics of contributing studies and results of meta-analyses). Up-to-date reporting guidance facilitates authors achieving this. 3

The Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) statement published in 2009 (hereafter referred to as PRISMA 2009) 4 5 6 7 8 9 10 is a reporting guideline designed to address poor reporting of systematic reviews. 11 The PRISMA 2009 statement comprised a checklist of 27 items recommended for reporting in systematic reviews and an “explanation and elaboration” paper 12 13 14 15 16 providing additional reporting guidance for each item, along with exemplars of reporting. The recommendations have been widely endorsed and adopted, as evidenced by its co-publication in multiple journals, citation in over 60 000 reports (Scopus, August 2020), endorsement from almost 200 journals and systematic review organisations, and adoption in various disciplines. Evidence from observational studies suggests that use of the PRISMA 2009 statement is associated with more complete reporting of systematic reviews, 17 18 19 20 although more could be done to improve adherence to the guideline. 21

Many innovations in the conduct of systematic reviews have occurred since publication of the PRISMA 2009 statement. For example, technological advances have enabled the use of natural language processing and machine learning to identify relevant evidence, 22 23 24 methods have been proposed to synthesise and present findings when meta-analysis is not possible or appropriate, 25 26 27 and new methods have been developed to assess the risk of bias in results of included studies. 28 29 Evidence on sources of bias in systematic reviews has accrued, culminating in the development of new tools to appraise the conduct of systematic reviews. 30 31 Terminology used to describe particular review processes has also evolved, as in the shift from assessing “quality” to assessing “certainty” in the body of evidence. 32 In addition, the publishing landscape has transformed, with multiple avenues now available for registering and disseminating systematic review protocols, 33 34 disseminating reports of systematic reviews, and sharing data and materials, such as preprint servers and publicly accessible repositories. To capture these advances in the reporting of systematic reviews necessitated an update to the PRISMA 2009 statement.

Summary points

To ensure a systematic review is valuable to users, authors should prepare a transparent, complete, and accurate account of why the review was done, what they did, and what they found

The PRISMA 2020 statement provides updated reporting guidance for systematic reviews that reflects advances in methods to identify, select, appraise, and synthesise studies

The PRISMA 2020 statement consists of a 27-item checklist, an expanded checklist that details reporting recommendations for each item, the PRISMA 2020 abstract checklist, and revised flow diagrams for original and updated reviews

We anticipate that the PRISMA 2020 statement will benefit authors, editors, and peer reviewers of systematic reviews, and different users of reviews, including guideline developers, policy makers, healthcare providers, patients, and other stakeholders

Development of PRISMA 2020

A complete description of the methods used to develop PRISMA 2020 is available elsewhere. 35 We identified PRISMA 2009 items that were often reported incompletely by examining the results of studies investigating the transparency of reporting of published reviews. 17 21 36 37 We identified possible modifications to the PRISMA 2009 statement by reviewing 60 documents providing reporting guidance for systematic reviews (including reporting guidelines, handbooks, tools, and meta-research studies). 38 These reviews of the literature were used to inform the content of a survey with suggested possible modifications to the 27 items in PRISMA 2009 and possible additional items. Respondents were asked whether they believed we should keep each PRISMA 2009 item as is, modify it, or remove it, and whether we should add each additional item. Systematic review methodologists and journal editors were invited to complete the online survey (110 of 220 invited responded). We discussed proposed content and wording of the PRISMA 2020 statement, as informed by the review and survey results, at a 21-member, two-day, in-person meeting in September 2018 in Edinburgh, Scotland. Throughout 2019 and 2020, we circulated an initial draft and five revisions of the checklist and explanation and elaboration paper to co-authors for feedback. In April 2020, we invited 22 systematic reviewers who had expressed interest in providing feedback on the PRISMA 2020 checklist to share their views (via an online survey) on the layout and terminology used in a preliminary version of the checklist. Feedback was received from 15 individuals and considered by the first author, and any revisions deemed necessary were incorporated before the final version was approved and endorsed by all co-authors.

The PRISMA 2020 statement

Scope of the guideline.

The PRISMA 2020 statement has been designed primarily for systematic reviews of studies that evaluate the effects of health interventions, irrespective of the design of the included studies. However, the checklist items are applicable to reports of systematic reviews evaluating other interventions (such as social or educational interventions), and many items are applicable to systematic reviews with objectives other than evaluating interventions (such as evaluating aetiology, prevalence, or prognosis). PRISMA 2020 is intended for use in systematic reviews that include synthesis (such as pairwise meta-analysis or other statistical synthesis methods) or do not include synthesis (for example, because only one eligible study is identified). The PRISMA 2020 items are relevant for mixed-methods systematic reviews (which include quantitative and qualitative studies), but reporting guidelines addressing the presentation and synthesis of qualitative data should also be consulted. 39 40 PRISMA 2020 can be used for original systematic reviews, updated systematic reviews, or continually updated (“living”) systematic reviews. However, for updated and living systematic reviews, there may be some additional considerations that need to be addressed. Where there is relevant content from other reporting guidelines, we reference these guidelines within the items in the explanation and elaboration paper 41 (such as PRISMA-Search 42 in items 6 and 7, Synthesis without meta-analysis (SWiM) reporting guideline 27 in item 13d). Box 1 includes a glossary of terms used throughout the PRISMA 2020 statement.

Glossary of terms

Systematic review —A review that uses explicit, systematic methods to collate and synthesise findings of studies that address a clearly formulated question 43

Statistical synthesis —The combination of quantitative results of two or more studies. This encompasses meta-analysis of effect estimates (described below) and other methods, such as combining P values, calculating the range and distribution of observed effects, and vote counting based on the direction of effect (see McKenzie and Brennan 25 for a description of each method)

Meta-analysis of effect estimates —A statistical technique used to synthesise results when study effect estimates and their variances are available, yielding a quantitative summary of results 25

Outcome —An event or measurement collected for participants in a study (such as quality of life, mortality)

Result —The combination of a point estimate (such as a mean difference, risk ratio, or proportion) and a measure of its precision (such as a confidence/credible interval) for a particular outcome

Report —A document (paper or electronic) supplying information about a particular study. It could be a journal article, preprint, conference abstract, study register entry, clinical study report, dissertation, unpublished manuscript, government report, or any other document providing relevant information

Record —The title or abstract (or both) of a report indexed in a database or website (such as a title or abstract for an article indexed in Medline). Records that refer to the same report (such as the same journal article) are “duplicates”; however, records that refer to reports that are merely similar (such as a similar abstract submitted to two different conferences) should be considered unique.

Study —An investigation, such as a clinical trial, that includes a defined group of participants and one or more interventions and outcomes. A “study” might have multiple reports. For example, reports could include the protocol, statistical analysis plan, baseline characteristics, results for the primary outcome, results for harms, results for secondary outcomes, and results for additional mediator and moderator analyses

PRISMA 2020 is not intended to guide systematic review conduct, for which comprehensive resources are available. 43 44 45 46 However, familiarity with PRISMA 2020 is useful when planning and conducting systematic reviews to ensure that all recommended information is captured. PRISMA 2020 should not be used to assess the conduct or methodological quality of systematic reviews; other tools exist for this purpose. 30 31 Furthermore, PRISMA 2020 is not intended to inform the reporting of systematic review protocols, for which a separate statement is available (PRISMA for Protocols (PRISMA-P) 2015 statement 47 48 ). Finally, extensions to the PRISMA 2009 statement have been developed to guide reporting of network meta-analyses, 49 meta-analyses of individual participant data, 50 systematic reviews of harms, 51 systematic reviews of diagnostic test accuracy studies, 52 and scoping reviews 53 ; for these types of reviews we recommend authors report their review in accordance with the recommendations in PRISMA 2020 along with the guidance specific to the extension.

How to use PRISMA 2020

The PRISMA 2020 statement (including the checklists, explanation and elaboration, and flow diagram) replaces the PRISMA 2009 statement, which should no longer be used. Box 2 summarises noteworthy changes from the PRISMA 2009 statement. The PRISMA 2020 checklist includes seven sections with 27 items, some of which include sub-items ( table 1 ). A checklist for journal and conference abstracts for systematic reviews is included in PRISMA 2020. This abstract checklist is an update of the 2013 PRISMA for Abstracts statement, 54 reflecting new and modified content in PRISMA 2020 ( table 2 ). A template PRISMA flow diagram is provided, which can be modified depending on whether the systematic review is original or updated ( fig 1 ).

Noteworthy changes to the PRISMA 2009 statement

Inclusion of the abstract reporting checklist within PRISMA 2020 (see item #2 and table 2 ).

Movement of the ‘Protocol and registration’ item from the start of the Methods section of the checklist to a new Other section, with addition of a sub-item recommending authors describe amendments to information provided at registration or in the protocol (see item #24a-24c).

Modification of the ‘Search’ item to recommend authors present full search strategies for all databases, registers and websites searched, not just at least one database (see item #7).

Modification of the ‘Study selection’ item in the Methods section to emphasise the reporting of how many reviewers screened each record and each report retrieved, whether they worked independently, and if applicable, details of automation tools used in the process (see item #8).

Addition of a sub-item to the ‘Data items’ item recommending authors report how outcomes were defined, which results were sought, and methods for selecting a subset of results from included studies (see item #10a).

Splitting of the ‘Synthesis of results’ item in the Methods section into six sub-items recommending authors describe: the processes used to decide which studies were eligible for each synthesis; any methods required to prepare the data for synthesis; any methods used to tabulate or visually display results of individual studies and syntheses; any methods used to synthesise results; any methods used to explore possible causes of heterogeneity among study results (such as subgroup analysis, meta-regression); and any sensitivity analyses used to assess robustness of the synthesised results (see item #13a-13f).

Addition of a sub-item to the ‘Study selection’ item in the Results section recommending authors cite studies that might appear to meet the inclusion criteria, but which were excluded, and explain why they were excluded (see item #16b).

Splitting of the ‘Synthesis of results’ item in the Results section into four sub-items recommending authors: briefly summarise the characteristics and risk of bias among studies contributing to the synthesis; present results of all statistical syntheses conducted; present results of any investigations of possible causes of heterogeneity among study results; and present results of any sensitivity analyses (see item #20a-20d).

Addition of new items recommending authors report methods for and results of an assessment of certainty (or confidence) in the body of evidence for an outcome (see items #15 and #22).

Addition of a new item recommending authors declare any competing interests (see item #26).

Addition of a new item recommending authors indicate whether data, analytic code and other materials used in the review are publicly available and if so, where they can be found (see item #27).

PRISMA 2020 item checklist

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PRISMA 2020 for Abstracts checklist*

PRISMA 2020 flow diagram template for systematic reviews. The new design is adapted from flow diagrams proposed by Boers, 55 Mayo-Wilson et al. 56 and Stovold et al. 57 The boxes in grey should only be completed if applicable; otherwise they should be removed from the flow diagram. Note that a “report” could be a journal article, preprint, conference abstract, study register entry, clinical study report, dissertation, unpublished manuscript, government report or any other document providing relevant information.

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We recommend authors refer to PRISMA 2020 early in the writing process, because prospective consideration of the items may help to ensure that all the items are addressed. To help keep track of which items have been reported, the PRISMA statement website ( http://www.prisma-statement.org/ ) includes fillable templates of the checklists to download and complete (also available in the data supplement on bmj.com). We have also created a web application that allows users to complete the checklist via a user-friendly interface 58 (available at https://prisma.shinyapps.io/checklist/ and adapted from the Transparency Checklist app 59 ). The completed checklist can be exported to Word or PDF. Editable templates of the flow diagram can also be downloaded from the PRISMA statement website.

We have prepared an updated explanation and elaboration paper, in which we explain why reporting of each item is recommended and present bullet points that detail the reporting recommendations (which we refer to as elements). 41 The bullet-point structure is new to PRISMA 2020 and has been adopted to facilitate implementation of the guidance. 60 61 An expanded checklist, which comprises an abridged version of the elements presented in the explanation and elaboration paper, with references and some examples removed, is available in the data supplement on bmj.com. Consulting the explanation and elaboration paper is recommended if further clarity or information is required.

Journals and publishers might impose word and section limits, and limits on the number of tables and figures allowed in the main report. In such cases, if the relevant information for some items already appears in a publicly accessible review protocol, referring to the protocol may suffice. Alternatively, placing detailed descriptions of the methods used or additional results (such as for less critical outcomes) in supplementary files is recommended. Ideally, supplementary files should be deposited to a general-purpose or institutional open-access repository that provides free and permanent access to the material (such as Open Science Framework, Dryad, figshare). A reference or link to the additional information should be included in the main report. Finally, although PRISMA 2020 provides a template for where information might be located, the suggested location should not be seen as prescriptive; the guiding principle is to ensure the information is reported.

Use of PRISMA 2020 has the potential to benefit many stakeholders. Complete reporting allows readers to assess the appropriateness of the methods, and therefore the trustworthiness of the findings. Presenting and summarising characteristics of studies contributing to a synthesis allows healthcare providers and policy makers to evaluate the applicability of the findings to their setting. Describing the certainty in the body of evidence for an outcome and the implications of findings should help policy makers, managers, and other decision makers formulate appropriate recommendations for practice or policy. Complete reporting of all PRISMA 2020 items also facilitates replication and review updates, as well as inclusion of systematic reviews in overviews (of systematic reviews) and guidelines, so teams can leverage work that is already done and decrease research waste. 36 62 63

We updated the PRISMA 2009 statement by adapting the EQUATOR Network’s guidance for developing health research reporting guidelines. 64 We evaluated the reporting completeness of published systematic reviews, 17 21 36 37 reviewed the items included in other documents providing guidance for systematic reviews, 38 surveyed systematic review methodologists and journal editors for their views on how to revise the original PRISMA statement, 35 discussed the findings at an in-person meeting, and prepared this document through an iterative process. Our recommendations are informed by the reviews and survey conducted before the in-person meeting, theoretical considerations about which items facilitate replication and help users assess the risk of bias and applicability of systematic reviews, and co-authors’ experience with authoring and using systematic reviews.

Various strategies to increase the use of reporting guidelines and improve reporting have been proposed. They include educators introducing reporting guidelines into graduate curricula to promote good reporting habits of early career scientists 65 ; journal editors and regulators endorsing use of reporting guidelines 18 ; peer reviewers evaluating adherence to reporting guidelines 61 66 ; journals requiring authors to indicate where in their manuscript they have adhered to each reporting item 67 ; and authors using online writing tools that prompt complete reporting at the writing stage. 60 Multi-pronged interventions, where more than one of these strategies are combined, may be more effective (such as completion of checklists coupled with editorial checks). 68 However, of 31 interventions proposed to increase adherence to reporting guidelines, the effects of only 11 have been evaluated, mostly in observational studies at high risk of bias due to confounding. 69 It is therefore unclear which strategies should be used. Future research might explore barriers and facilitators to the use of PRISMA 2020 by authors, editors, and peer reviewers, designing interventions that address the identified barriers, and evaluating those interventions using randomised trials. To inform possible revisions to the guideline, it would also be valuable to conduct think-aloud studies 70 to understand how systematic reviewers interpret the items, and reliability studies to identify items where there is varied interpretation of the items.

We encourage readers to submit evidence that informs any of the recommendations in PRISMA 2020 (via the PRISMA statement website: http://www.prisma-statement.org/ ). To enhance accessibility of PRISMA 2020, several translations of the guideline are under way (see available translations at the PRISMA statement website). We encourage journal editors and publishers to raise awareness of PRISMA 2020 (for example, by referring to it in journal “Instructions to authors”), endorsing its use, advising editors and peer reviewers to evaluate submitted systematic reviews against the PRISMA 2020 checklists, and making changes to journal policies to accommodate the new reporting recommendations. We recommend existing PRISMA extensions 47 49 50 51 52 53 71 72 be updated to reflect PRISMA 2020 and advise developers of new PRISMA extensions to use PRISMA 2020 as the foundation document.

We anticipate that the PRISMA 2020 statement will benefit authors, editors, and peer reviewers of systematic reviews, and different users of reviews, including guideline developers, policy makers, healthcare providers, patients, and other stakeholders. Ultimately, we hope that uptake of the guideline will lead to more transparent, complete, and accurate reporting of systematic reviews, thus facilitating evidence based decision making.

Acknowledgments

We dedicate this paper to the late Douglas G Altman and Alessandro Liberati, whose contributions were fundamental to the development and implementation of the original PRISMA statement.

We thank the following contributors who completed the survey to inform discussions at the development meeting: Xavier Armoiry, Edoardo Aromataris, Ana Patricia Ayala, Ethan M Balk, Virginia Barbour, Elaine Beller, Jesse A Berlin, Lisa Bero, Zhao-Xiang Bian, Jean Joel Bigna, Ferrán Catalá-López, Anna Chaimani, Mike Clarke, Tammy Clifford, Ioana A Cristea, Miranda Cumpston, Sofia Dias, Corinna Dressler, Ivan D Florez, Joel J Gagnier, Chantelle Garritty, Long Ge, Davina Ghersi, Sean Grant, Gordon Guyatt, Neal R Haddaway, Julian PT Higgins, Sally Hopewell, Brian Hutton, Jamie J Kirkham, Jos Kleijnen, Julia Koricheva, Joey SW Kwong, Toby J Lasserson, Julia H Littell, Yoon K Loke, Malcolm R Macleod, Chris G Maher, Ana Marušic, Dimitris Mavridis, Jessie McGowan, Matthew DF McInnes, Philippa Middleton, Karel G Moons, Zachary Munn, Jane Noyes, Barbara Nußbaumer-Streit, Donald L Patrick, Tatiana Pereira-Cenci, Ba’ Pham, Bob Phillips, Dawid Pieper, Michelle Pollock, Daniel S Quintana, Drummond Rennie, Melissa L Rethlefsen, Hannah R Rothstein, Maroeska M Rovers, Rebecca Ryan, Georgia Salanti, Ian J Saldanha, Margaret Sampson, Nancy Santesso, Rafael Sarkis-Onofre, Jelena Savović, Christopher H Schmid, Kenneth F Schulz, Guido Schwarzer, Beverley J Shea, Paul G Shekelle, Farhad Shokraneh, Mark Simmonds, Nicole Skoetz, Sharon E Straus, Anneliese Synnot, Emily E Tanner-Smith, Brett D Thombs, Hilary Thomson, Alexander Tsertsvadze, Peter Tugwell, Tari Turner, Lesley Uttley, Jeffrey C Valentine, Matt Vassar, Areti Angeliki Veroniki, Meera Viswanathan, Cole Wayant, Paul Whaley, and Kehu Yang. We thank the following contributors who provided feedback on a preliminary version of the PRISMA 2020 checklist: Jo Abbott, Fionn Büttner, Patricia Correia-Santos, Victoria Freeman, Emily A Hennessy, Rakibul Islam, Amalia (Emily) Karahalios, Kasper Krommes, Andreas Lundh, Dafne Port Nascimento, Davina Robson, Catherine Schenck-Yglesias, Mary M Scott, Sarah Tanveer and Pavel Zhelnov. We thank Abigail H Goben, Melissa L Rethlefsen, Tanja Rombey, Anna Scott, and Farhad Shokraneh for their helpful comments on the preprints of the PRISMA 2020 papers. We thank Edoardo Aromataris, Stephanie Chang, Toby Lasserson and David Schriger for their helpful peer review comments on the PRISMA 2020 papers.

Contributors: JEM and DM are joint senior authors. MJP, JEM, PMB, IB, TCH, CDM, LS, and DM conceived this paper and designed the literature review and survey conducted to inform the guideline content. MJP conducted the literature review, administered the survey and analysed the data for both. MJP prepared all materials for the development meeting. MJP and JEM presented proposals at the development meeting. All authors except for TCH, JMT, EAA, SEB, and LAM attended the development meeting. MJP and JEM took and consolidated notes from the development meeting. MJP and JEM led the drafting and editing of the article. JEM, PMB, IB, TCH, LS, JMT, EAA, SEB, RC, JG, AH, TL, EMW, SM, LAM, LAS, JT, ACT, PW, and DM drafted particular sections of the article. All authors were involved in revising the article critically for important intellectual content. All authors approved the final version of the article. MJP is the guarantor of this work. The corresponding author attests that all listed authors meet authorship criteria and that no others meeting the criteria have been omitted.

Funding: There was no direct funding for this research. MJP is supported by an Australian Research Council Discovery Early Career Researcher Award (DE200101618) and was previously supported by an Australian National Health and Medical Research Council (NHMRC) Early Career Fellowship (1088535) during the conduct of this research. JEM is supported by an Australian NHMRC Career Development Fellowship (1143429). TCH is supported by an Australian NHMRC Senior Research Fellowship (1154607). JMT is supported by Evidence Partners Inc. JMG is supported by a Tier 1 Canada Research Chair in Health Knowledge Transfer and Uptake. MML is supported by The Ottawa Hospital Anaesthesia Alternate Funds Association and a Faculty of Medicine Junior Research Chair. TL is supported by funding from the National Eye Institute (UG1EY020522), National Institutes of Health, United States. LAM is supported by a National Institute for Health Research Doctoral Research Fellowship (DRF-2018-11-ST2-048). ACT is supported by a Tier 2 Canada Research Chair in Knowledge Synthesis. DM is supported in part by a University Research Chair, University of Ottawa. The funders had no role in considering the study design or in the collection, analysis, interpretation of data, writing of the report, or decision to submit the article for publication.

Competing interests: All authors have completed the ICMJE uniform disclosure form at http://www.icmje.org/conflicts-of-interest/ and declare: EL is head of research for the BMJ ; MJP is an editorial board member for PLOS Medicine ; ACT is an associate editor and MJP, TL, EMW, and DM are editorial board members for the Journal of Clinical Epidemiology ; DM and LAS were editors in chief, LS, JMT, and ACT are associate editors, and JG is an editorial board member for Systematic Reviews . None of these authors were involved in the peer review process or decision to publish. TCH has received personal fees from Elsevier outside the submitted work. EMW has received personal fees from the American Journal for Public Health , for which he is the editor for systematic reviews. VW is editor in chief of the Campbell Collaboration, which produces systematic reviews, and co-convenor of the Campbell and Cochrane equity methods group. DM is chair of the EQUATOR Network, IB is adjunct director of the French EQUATOR Centre and TCH is co-director of the Australasian EQUATOR Centre, which advocates for the use of reporting guidelines to improve the quality of reporting in research articles. JMT received salary from Evidence Partners, creator of DistillerSR software for systematic reviews; Evidence Partners was not involved in the design or outcomes of the statement, and the views expressed solely represent those of the author.

Provenance and peer review: Not commissioned; externally peer reviewed.

Patient and public involvement: Patients and the public were not involved in this methodological research. We plan to disseminate the research widely, including to community participants in evidence synthesis organisations.

This is an Open Access article distributed in accordance with the terms of the Creative Commons Attribution (CC BY 4.0) license, which permits others to distribute, remix, adapt and build upon this work, for commercial use, provided the original work is properly cited. See: http://creativecommons.org/licenses/by/4.0/ .

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• Nakagawa S ,
• Liberati A ,
• Tetzlaff J ,
• Altman DG ,
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• de Belvis G ,
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• Ajamieh S ,
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• McNaught J ,
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Treatment of women with diastasis recti: HTA Report [Internet]. Stockholm: Swedish Agency for Health Technology Assessment and Assessment of Social Services (SBU); 2022 Mar 15. (SBU Assessment, No. 346.)

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SYSTEMATIC REVIEW article

Research of visual attention networks in deaf individuals: a systematic review.

• 1 Department of Psychology, University of Almería, Almería, Spain
• 2 CIBIS Research Center, University of Almería, Almería, Spain
• 3 Growing Brains, Washington, DC, United States

The impact of deafness on visual attention has been widely discussed in previous research. It has been noted that deficiencies and strengths of previous research can be attributed to temporal or spatial aspects of attention, as well as variations in development and clinical characteristics. Visual attention is categorized into three networks: orienting (exogenous and endogenous), alerting (phasic and tonic), and executive control. This study aims to contribute new neuroscientific evidence supporting this hypothesis. This paper presents a systematic review of the international literature from the past 15 years focused on visual attention in the deaf population. The final review included 24 articles. The function of the orienting network is found to be enhanced in deaf adults and children, primarily observed in native signers without cochlear implants, while endogenous orienting is observed only in the context of gaze cues in children, with no differences found in adults. Results regarding alerting and executive function vary depending on clinical characteristics and paradigms used. Implications for future research on visual attention in the deaf population are discussed.

1 Introduction

1.1 background.

Early auditory deprivation is recognized as a factor influencing the development of visual attention in deaf individuals ( Colmenero et al., 2004 ; Bavelier et al., 2006 ; Stevens and Neville, 2006 ). However, existing evidence on the nature of this effect is conflicting and, crucially for the present review, unclear concerning the temporal versus spatial distribution of visual attention. Historically, research on this topic has been centered on two seemingly opposing hypotheses: the deficiency hypothesis, positing that early profound deafness leads to visual attention deficits, and the enhancement hypothesis, suggesting compensatory changes to visual attention processes ( Dye and Bavelier, 2010 ).

According to the deficiency hypothesis , integrating information from different senses is essential for the normal development of attention functioning within each sensory modality. Consequently, the absence of auditory input results in underdeveloped selective attention capacities. For deaf individuals, the lack of audition impairs the development of multisensory integration, thereby impeding the typical development of visual attention skills. Put simply, while hearing people can selectively attend to a narrow visual field and still monitor the broader environment through sounds, deaf individuals must use vision to accomplish both specific tasks and monitor the broader environment ( Smith et al., 1998 ).

This view has been primarily supported by studies examining sustained visual attention or vigilance using the Continuous Performance Test or “CPT.” For example, using the Gordon Diagnostic System (GDS), a widely used CPT, the participant is presented with digits and must respond when a “1” is followed by a “9” for around 10 min ( Dye and Hauser, 2014 ). These studies have found consistent underperformance in CPTs among the deaf population, indicating that auditory input plays a role in organizing visual attention. These results are consistent with a deficit view of cross-modal reorganization stemming from early sensory deprivation ( Mitchell and Quittner, 1996 ; Smith et al., 1998 ; Quittner et al., 2004 ).

Although CPTs have been widely used to assess sustained visual attention, these tasks are sensitive to certain additional cognitive factors ( Parasnis et al., 2003 ). Specifically, CPTs require sustained attention and the ability to hold information about the target sequence in working memory, and performance is negatively affected by the inability to inhibit responses to non-target stimuli.

In contrast to the deficiency hypothesis, the enhancement hypothesis or compensation view is based on the common assumption that deficits in one sensory modality lead to heightened sensitivities in the remaining modalities ( Bavelier et al., 2006 ). In the case of early deafness, this perspective posits that the visual system is reorganized to compensate for the lack of auditory input. Consequently, visual skills assume the functional roles previously performed by audition in the typically developing child, such as monitoring the environment or discriminating temporally complex stimuli ( Bottari et al., 2014 ; Benetti et al., 2017 ; Bola et al., 2017 ; Seymour et al., 2017 ).

The enhancement or compensation hypothesis has primarily received support from studies measuring the allocation of attention across space. The results of these studies suggest that in deaf individuals, there is a spatial redistribution of visual attention toward the periphery, allowing them to better monitor their peripheral environment based on visual rather than auditory cues ( Loke and Song, 1991 ; Sladen et al., 2005 ). For example, deaf individuals can be faster than hearing controls in detecting the onset of peripheral visual targets ( Chen et al., 2006 ; Bottari et al., 2010 ; Codina et al., 2011 , 2017 ) or in discriminating the direction of visual motion with attention to peripheral locations ( Neville and Lawson, 1987 ; Bavelier et al., 2001 ).

This redistribution of visual attention can alter the trade-off in the responses of deaf people to the periphery versus the centre. Specifically, in situations where central and peripheral static stimuli compete for selective attention resources, deaf participants are more likely to orient visual attention toward peripheral than central locations ( Sladen et al., 2005 ; Chen et al., 2006 ). Consistent with these findings, Proksch and Bavelier (2002) observed that deaf individuals are more distracted by irrelevant peripheral information, whereas hearing individuals are more distracted by irrelevant central information. However, while deaf individuals have been shown to possess a field of view that extends further toward the periphery than hearing controls ( Sladen et al., 2005 ), no differences between deaf individuals and hearing controls have been documented when processing targets presented toward the centre of the visual field ( Neville and Lawson, 1987 ; Loke and Song, 1991 ).

In an initial review conducted by Tharpe et al. (2008) to examine evidence-based literature on visual attention and deafness, various paradigms were explored, including the CPT, the letter cancellation task, and conflict tasks. No conclusive evidence was found to support general enhancement or deficits in visual attention or enhanced fundamental visual sensory abilities ( Tharpe et al., 2002 ). Rather, the authors propose that the variability in performance across these paradigms could be explained by the extensive allocation of attentional resources across the visual field, driven by increased monitoring demands. This hypothesis explains why deaf individuals tend to show poorer performance on tasks requiring sustained attention to central stimuli over time compared to those involving the detection of peripheral stimuli. This idea has been supported by results found using a modified flanker paradigm incorporating several degrees of distance between distractor and target ( Sladen et al., 2005 ).

Functional brain studies have also revealed significant differences between deaf and hearing individuals that support the compensation view. These differences are related to alterations in the visual areas and the activation of visual and attention-related brain networks. For instance, Bavelier et al. (2001) found that the absence of auditory input and sign language use in the deaf population was associated with greater activation of visual cortex areas when processing peripheral and moving stimuli. Furthermore, Mayberry et al. (2011) reported that deaf individuals exhibited greater activation of visual and attention-related brain networks during peripheral visual tasks.

An area of the cortex that has been extensively studied in the context of deafness is the middle temporal (MT) or medial superior temporal (MST) area. MT/MST areas play a key role in detecting and analyzing movement and activity in these areas is modulated by attentional processes ( O’Craven et al., 1997 ). When observing unattended moving stimuli, both deaf and hearing participants show similar recruitment of the MT/MST cortex. However, when required to attend to peripheral movement and ignore concurrent central motion, enhanced recruitment of the MT/MST is observed in deaf individuals relative to hearing controls ( Bavelier et al., 2001 ; Fine et al., 2005 ). This pattern echoes a general trend in the literature, where the most significant population differences have been reported for motion stimuli in the visual periphery under conditions that engage selective attention, such as when the location or time of arrival of the stimulus is unknown or when the stimulus must be selected from distractors ( Bavelier et al., 2006 ). These findings suggest that deafness is associated with alterations in visual attention, resulting in changes in the recruitment of brain networks involved in the processing of visual information.

These apparently contradictory hypotheses highlight the necessity of organising previous research within a recognized model of attention. This review aims to respond to this need by systematically analysing the tasks employed to measure various aspects of attention in each study.

1.2 The integrative hypothesis

The contradictory results mentioned previously prompted an integrative review published by Dye and Bavelier (2010) . These authors proposed that while the deficiency hypothesis and enhancement hypothesis may appear to be mutually exclusive, the conflicting evidence concerning the impact of deafness on visual attention could arise from measuring different aspects of visual attention. Consequently, the deficit view is predominantly supported by studies focused on the allocation of attention over time, whereas the compensation view is backed by studies measuring the allocation of attention across space. Therefore, when considering different aspects of visual attention, a striking pattern of attentional enhancements and deficits emerges as a consequence of early deafness.

In addition, these two perspectives consider groups of different ages and backgrounds. Individuals in the deaf and hard of hearing population are quite diverse regarding their preferred mode of communication (sign language versus oral language), the age of acquisition of their native language, the hearing status of their parents, the aetiology of hearing loss (e.g., genetic, infection), and the implantation of cochlear implants [CI—a small electronic device that is surgically implanted into the inner ear to help provide a sense of sound to individuals with severe to profound hearing loss ( Wilson and Dorman, 2008 )]. Most of the research suggesting that deaf children have problems with visual attention has focused on deaf children learning spoken language, examining changes in sustained visual attention after restoration of auditory input through a CI ( Mitchell and Quittner, 1996 ; Smith et al., 1998 ; Quittner et al., 2004 ). In contrast, studies suggesting that the visual system compensates for the lack of auditory input by enhancing the monitoring of the peripheral visual field have primarily involved deaf adults. Specifically, these studies have focused on culturally deaf individuals born to Deaf parents, acquiring American Sign Language (ASL) as their first language and lacking CI. This group is compared to those who received oral speech therapy and have CI ( Bavelier et al., 2006 ; Dye et al., 2009 ).

Dye and Bavelier (2010) suggested that the deficiency and compensatory views were not necessarily contradictory but complementary in explaining the cross-modal reorganization of visual attention after early deafness. They propose an integrative view in which early auditory deprivation does not have an overall positive or negative impact on visual attention, but rather, selected aspects of visual attention are modified in various ways throughout the developmental trajectory.

However, this division of visual attention in temporal and spatial aspects is very broad, and the paradigms used to test these hypotheses have certain shortcomings. Studies examining the impact on temporal attention used measures from the Rapid Serial Visual Presentation Paradigms and the Attentional Blink; however, consistent results were not observed across different experiments ( Dye and Bavelier, 2010 ; Dye, 2014 ; Thakur et al., 2019 ). Concerning spatial attention, the Useful Field Of View (UFOV) task has been employed. However, this complex dual task requires following two instructions — to both detect and locate a target while ignoring several distractors. Consequently, working memory, inhibition, orienting, and divided attention can all be deployed in this task, giving rise to what is referred to as the task impurity problem ( Miyake et al., 2000 ).

1.3 The attention networks model

Understanding the potential deficits and enhancements in visual attention among deaf individuals requires recognizing that visual attention is not a unitary entity. From this perspective, based on behavioral and neuroscientific studies, Posner and colleagues have suggested a model that divides the human attentional system into three functionally and anatomically independent networks responsible for alerting, orienting, and executive attention ( Fan et al., 2002 , 2005 ; Posner and Rothbart, 2007 ; Petersen and Posner, 2012 ). As already mentioned, previous hypotheses suggest that various aspects of visual attention can be affected differently in deaf individuals due to compensatory changes. The attentional networks model offers a framework to measure these different changes by separating attention into several functions.

The alerting network is responsible for achieving and maintaining a state of elevated sensitivity to incoming information. Alertness can be further subdivided into tonic and phasic alertness (for a review, see Sturm and Willmes, 2001 ). Tonic alertness (also called vigilance or sustained attention) is a state of general wakefulness or vigilance and refers to the ability to sustain attention over a period of time. Phasic alertness is a more transient alert state, modulated by a warning that precedes a target stimulus and prepares the individual for a fast reaction. Performance within this network has been measured using tasks where the appearance of the target is preceded by an anticipatory alerting cue, provoking a phasic change in alertness. This transition involves a shift from a resting state to a prepared state, ready to detect and respond to an expected event ( Marrocco and Davidson, 1998 ; Beane and Marrocco, 2004 ). Tonic alertness, on the other hand, is typically evaluated through lengthy and repetitive tasks requiring participants to identify and respond to infrequently occurring targets, the most frequent example being CPTs ( Petersen and Posner, 2012 ).

The orienting network is responsible for the movement of attention throughout space, allowing the selection of specific information from numerous sensory inputs. In this regard, orienting can be reflexive ( exogenous ), such as when a sudden target event draws attention to its location, or it can be voluntary ( endogenous ), such as when a person searches the visual field looking for a target ( Jonides, 1981 ). Although overt orienting is often associated with head or eye movements toward the target, it can also enhance target processing by covertly orienting attention ( Posner, 1980 , 2016 ). Spatial orientation has traditionally been studied with tasks based on the “spatial orienting paradigm” or “cost and benefits paradigm.” In these tasks, the participants are presented with a fixation point and placeholders (the location where the target appears) at both sides of a fixation point. Following the onset of the fixation point, an attentional cue is presented, followed by the target to which participants must respond. Trials are categorized as cued/valid if the target appears at cued locations, uncued/invalid when it appears opposite to the cue, or neutral when the cue appears at the centre or both locations. In typical measures of exogenous orienting, a change occurs in the placeholder location to elicit an involuntary orienting response (such as the illumination of the locations). Conversely, in measures of endogenous orienting, a central cue is presented to prompt a voluntary orienting response toward a specific location or object ( Uncapher et al., 2011 ; Chica et al., 2014 ).

Finally, the executive attention network involves more complex mental operations to detect and resolve the conflict between expectation, stimulus, and response. While this network shares some overlap with executive functions, it specifically involves processes related to planning and executing goal-directed actions. However, executive functions are a more general domain that includes working memory, mental flexibility, conflict monitoring, and, in close association with executive attention, inhibitory control ( Botvinick et al., 2001 ; Matsumoto and Tanaka, 2004 ). Assessment of the executive attention network typically involves “resolution of conflict” paradigms, which require the suppression of either processing or responding to information that elicits incorrect or inappropriate responses ( Posner and DiGirolamo, 1998 ). Examples of such paradigms include the flanker ( Fan et al., 2002 ), Stroop ( Fan et al., 2003 ), or Simon tasks ( Simon and Craft, 1970 ).

One commonly used task specifically designed to measure most of these networks is the attention network test (ANT), which is based on two paradigms — the flanker task and the cost and benefits paradigm. The ANT enables the evaluation of three attentional networks in children and adults: phasic alerting, exogenous orienting, and executive attention ( Fan et al., 2002 ).

The main task is based on the flanker paradigm where the participant must press two keys indicating the direction (left or right) of a central arrow surrounded by congruent, incongruent, or neutral flankers. The difference in reaction times or accuracy between the congruent and incongruent conditions provides a measure of the executive attention network. The efficiency of the alerting network is examined by changes in performance resulting from a warning signal preceding the target, compared to trials without any previous cue. The efficiency of the orienting network is measured by comparing the performance benefits associated with a spatial cue predicting the location of the stimulus array (above or below fixation) with a central cue.

The integrative hypothesis proposed by Dye and Bavelier (2010) predicts that the strengths and weaknesses in visual attention resulting from early auditory deprivation are also linked to the abilities of orienting, alerting, and executive functions within the visual attention networks model developed by Petersen and Posner (2012) . Consequently, it is important to identify the tasks used to measure attention in deaf individuals and their possible interpretation according to the attention networks model. Understanding the weaknesses and strengths of visual attention networks related to early auditory deprivation aids in characterizing the developmental trajectory of these attentional functions during middle childhood (from 6 to 12 years old) since this is an important developmental stage for visual attention ( Rueda et al., 2004 ) and marks the beginning of formal schooling.

1.4 Objectives

To our knowledge, no systematic review has included evidence regarding the integrative hypothesis proposed by Dye and Bavelier (2010) . Furthermore, since the publication of the 2008 review by Tharpe and colleagues, no comprehensive review has been conducted to gather research findings enabling the identification of visual attention functions that could be diminished or enhanced in individuals with early auditory deprivation.

We conducted a systematic review of studies published between 2008 and 2023 focusing on deaf populations (from middle childhood through adulthood). The objective was to analyse investigations exploring one or more visual attention functions described in the attentional networks model. More specifically, our systematic review aims to:

1. Determine the most frequently studied functions of alerting, orienting, and executive attention in deaf individuals, along with the task paradigms employed to investigate such functions.

2. Identify the main strengths and impairments observed in the functioning of attentional networks in deaf adults and explore whether differences are found depending on the use of different communication systems, cochlear implants, and age of cochlear implant acquisition.

3. Examine the key developmental changes observed in the functioning of attention networks in deaf children during middle childhood (ages 6–12) and identify the main differences compared to typical hearing children of the same age.

2.1 Search strategy

We conducted a search on October 9th, 2023, of the peer-reviewed literature published in English between 2008 and 2023. The search was carried out on the Web of Science, Medline, Scielo, and Psycinfo databases, focusing on experimental studies of deaf populations aged 6–50 years. Using performance tasks to measure visual attention. The search utilized specific terms with relevant connectors to target visual attention measures and the population of interest. The search terms included: (deaf* OR “auditory deprivation” OR “hearing impairment”) AND (“orient*” OR “alert*” OR “spatial attention” OR “attention network” OR “visual selective attention” OR “visual attention” OR “sustained attention” OR “altered attention” OR “divided attention” OR “visuospatial attention” OR “executive attention”). Data extraction adhered to the recommendations provided by the Cochrane group ( Higgins and Green, 2011 ) and the Preferred Reporting Items for Systematic Review and Meta-Analyses protocol (PRISMA; Moher et al., 2009 ).

2.2 Selection criteria

We use the PICOS strategy to define inclusion criteria (Participants, Intervention, Comparisons, Results, and Studies). This review includes studies with the following characteristics: (P) participants without a psychiatric history and typical neurodevelopment with mild, severe, or profound bilateral deafness aged between 6 and 50 year; (I) measures of some of the specific functions of the attention networks, including alerting orienting and executive attention. No specific intervention is considered in this review; (C) Transversal studies comparing performance between the deaf and typical hearing population, studies that compare the deaf population across different clinical variables such as CI and system of communication, and longitudinal studies within the deaf population assessing the development of visual attention; (O) studies are included where at least some of the attention networks can be separately measured through performance-based tasks based on the previously mentioned paradigms; and (S) Single case studies, doctoral theses, conference presentations, and papers without peer review are excluded.

2.3 Data extraction and quality evaluation

The initial search yielded 2,603 articles. After excluding duplicates between databases, 1,349 articles were removed. After applying the exclusion criteria, the studies were filtered by title and abstract, resulting in 86 remaining papers by the first author. The full texts of these 86 articles were then read and analysed by all authors. Most articles were excluded due to the inclusion of populations with other deficits, non-performance-based measures, or tasks that measured other aspects of visual attention not included in the attention networks model. In total, 24 articles met our inclusion criteria in agreement with all authors (see Figure 1 ).

Figure 1 . Flow chart of the identification, screening, eligibility, and selection of studies.

Based on our research objective, the articles were classified according to the age of the participants: individuals aged 18 to 60 were categorized as adults, while those aged 6 to 12 were considered children. After some deliberation among the authors, studies involving participants up to 14 years old were included in the children category, along with a study by Kronenberger et al. (2013) which encompassed individuals aged 7–25 years. Significant statistical differences between deaf or hard of hearing and fully hearing individuals in measures assessing attention network efficiency were used as an indication of specific outcomes for each study.

The risk of bias was assessed for all articles using the Newcastle-Ottawa scale (NOS; Wells et al., 2021 , adapted from Herzog et al., 2013 ) to evaluate the quality of the studies. In this version, the quality scores were based on the selection of sample, comparability between groups, and the measurement of results. For cross-sectional studies, a maximum score of 10 can be obtained, with a score above 6 considered a satisfactory methodology score ( Orton et al., 2014 ). In this systematic review, none of the studies included in the final analysis scored <7 (see Table 1 ).

Table 1 . Risk of bias scores adapted from the Newcastle-Ottawa scale.

3.1 Frequency of studies and tasks used

The initial objective of the study was to determine the most frequently studied aspects of attention. Of the 24 included studies, 23 adopted a cross-sectional experimental design and one was a longitudinal study. Additionally, 15 studies focused solely on adult samples, eight studies exclusively involved children, and one study included both adult and child participants. Not all studies investigated a single attention network (see Table 2 ).

Table 2 . Studies included in the review by group of age sample and function measured.

3.1.1 The alerting network

The alerting network was studied in 8 of 24 articles. Among these studies, five exclusively involved children aged between 6 and 12 years, two studies focused on adults aged between 19 and 57, and one study used a mixed sample of adults and children aged between 7 and 25. Except for two of the 11 studies ( Daza and Phillips-Silver, 2013 ; Bharadwaj et al., 2020 ), the rest compared the deaf group with their hearing peers. Six of the 11 studied the tonic alerting network using CPTs, while one studied phasic alerting using the ANT (see Table 3 ).

Table 3 . Paradigms used in the studies included in the review.

As mentioned above, CPTs are frequently used to measure visual attention in deaf individuals. Depending on the paradigm used, several interpretations are possible regarding the specific function measured. Following the previously described example of the GDS, commission errors due to responding to “9” when no “1” appeared are considered impulsive, lack of response or omission errors are considered distraction/inattention, and the most commonly used “ d ’” combines commission and omission errors to obtain a measure of sensitivity and is considered to show vigilance, which is why it has been classified as a tonic alerting measure ( Baijot et al., 2013 ).

3.1.2 The orienting network

The orienting network was studied in 12 of the 24 articles. Only two studies focused on children, one involving a sample aged between 6 and 14 years and another involving both children and adults aged between 10 and 58. The majority of studies (seven out of 12) were conducted exclusively with adults aged between 18 and 57. In eight out of 12 articles, exogenous orienting was studied, using spatial orienting paradigms, including the ANT. Four articles investigated endogenous orienting using spatial orienting paradigms. A visual search paradigm designed by Heimler et al. (2015a) allows for obtaining a measure of exogenous and endogenous orienting and was included in both categories (see Table 3 ).

As mentioned previously, the orienting paradigms facilitate the measurement of exogenous and endogenous orienting by manipulating cues before the appearance of targets. These paradigms provide various measures of the orienting process, the most common being the facilitation of a valid cue toward the target. Additionally, they can be used to measure the disengagement of attention following an invalid cue. In cases where eye movements are considered, overt orienting of attention is measured instead of covert attention. Four of the nine studies focusing on exogenous attention with orienting paradigms measured saccadic eye movements (overt attention), while the remaining five used only manual responses (covert attention). Heimler et al. (2015a) designed a visual search paradigm in which participants must search for a target (tilted line) among a visual field full of similar distractors (straight lines) while ignoring a salient distractor (line tilted opposite direction). The salience of the target and distractor was manipulated trial by trial by changing their colors. This approach was driven by the idea that the salient stimulus attracts exogenous attention while the target requires an endogenous search across the visual field. Through this method, they were able to obtain a measure of endogenous orienting and exogenous orienting.

3.1.3 The executive attention network

The executive attention network was studied in 7 of 24 articles. Four studies involved a sample of children aged between 6 and 13 (see Figure 2 ), while three focused exclusively on adults aged between 18 and 58 (see Figure 3 ). Three of the 7 used conflict tasks with several modifications, three used the ANT, and the remainder employed the modified CPT developed by Dye and Hauser (2014) (see Table 3 ).

Figure 2 . Number of studies with deaf children in each attention network function and the general findings in comparison to full hearing children. *Deficits in executive attention found with younger children [2, 74].

Figure 3 . Number of studies with deaf adults in each attention network function and the general findings in comparison to full hearing adults. *Enhancements found in overt orienting but not in covert orienting and deficits with executive attention found only during specific conditions.

Regarding measures of executive attention, paradigms classified as conflict tasks were included. These tasks require participants to ignore distractors while attending to a central target. Notably, the study conducted by Dye and Hauser (2014) used a CPT but compared the execution of a CPT with and without distractors in the same sample, thereby measuring executive attention.

3.2 Comparisons between deaf and hearing adults

Our second objective was to compile the differences found between deaf and full hearing adults. We note that all studies involving adults employed a cross-sectional design (see Figure 2 ). The two studies that measured tonic alerting in deaf adults revealed poorer performance compared to hearing peers when using CPTs as a measure ( Kronenberger et al., 2013 ; Bharadwaj et al., 2020 ). Specifically, Kronenberger et al. (2013) used the Test of Variables of Attention (TOVA), indicating poorer performance by deaf individuals across all measures. Similarly, Bharadwaj et al. (2020) used the Integrated Visual and Auditory Continuous Performance Test (IVA plus CPT), demonstrating that deaf individuals commit more omission errors and have slower reaction times.

The only study that measured phasic alerting with alerting cues found an advantage in deaf adults ( Prasad et al., 2022 ). Deaf adults also seem to have advantages in covert exogenous orienting ( Xingjuan et al., 2011 ; Brazão et al., 2021 ; Li et al., 2022 ; Prasad et al., 2022 ). However, studies that measured overt attention with saccadic movement found no facilitation of exogenous orienting with this measure ( Bottari et al., 2012 ; Prasad et al., 2015 ; Heimler et al., 2015a ; Jayaraman et al., 2016 ). The five studies that measured endogenous orienting found no differences between deaf and full-hearing adults ( Bottari et al., 2008 ; Heimler et al., 2015a , b ; Bonmassar et al., 2021 ; Li et al., 2022 ).

Regarding executive attention, no differences were found between deaf adults and their hearing peers in a typical flanker task ( Holmer et al., 2020 ). Chen et al. (2010) used a paradigm with three conditions: congruency, the distance of the distractor (central or peripheral), and screen proximity (typical computer screen or projected onto a wall) and found that deaf adults showed greater interference from peripheral distractors compared to central cues. This effect was reversed when the display was projected onto a wall. Hauthal et al. (2012) designed a paradigm where participants had to discern the gender of a central target while faces appeared as distractors at the flanks. The faces could either match or differ in gender from the target, creating interference. The study revealed that with a high volume of distractors, adult deaf signers without CI still showed interference effects while hearing adults did not.

Regarding our secondary objective, to explore any differences observed among deaf individuals in relation to variables concerning hearing loss history, device use and mode of communication, very few studies examined adults with CI (see Table 4 ), possibly due to the relative novelty of the technology ( Wilson and Dorman, 2008 ). The few studies that included adults with CI did not find any effect of implantation in tonic alerting ( Kronenberger et al., 2013 ; Bharadwaj et al., 2020 ). The rest of the findings will be discussed below along with the results of studies in children.

Table 4 . Basic deaf related variables regarding auditory access and system of communication.

3.3 Development of attention networks and comparison between deaf and full hearing children

With respect to our third and final objective, we found one longitudinal study and four studies that either compared groups across different ages or treated age as a continuous independent variable. In deaf individuals, tonic alerting was observed to develop between 6 and 13 years of age ( Dye and Hauser, 2014 ; Dye and Terhune-Cotter, 2023 ). With exogenous orienting, the only result found was that the fundamental operations of moving and engaging develop from 6 to 7 years of age ( Daza and Phillips-Silver, 2013 ). Lastly, executive attention appears to develop around 8 years of age in deaf individuals ( Dye and Hauser, 2014 ). As mentioned before, comparisons between differences between individuals with and without CIs and different systems of communication were almost exclusive to studies with children. When comparing deaf and typical hearing children, greater challenges in tonic alertness were evident in speaking deaf children with CI ( Yucel and Derim, 2008 ; Hoffman et al., 2018 ), but not in deaf signers without CI ( Dye and Hauser, 2014 ). Regarding phasic alertness, Daza and Phillips-Silver (2013) found a greater alerting effect in the ANT when comparing oral deaf children with CI and deaf signers without CI. Daza and Phillips-Silver (2013) also found faster movement and engagement in a spatial orienting paradigm when comparing deaf signers without CI to oral deaf children with CI. However, in endogenous orienting, an advantage was found in deaf children (independent of the system of communication) when a social central cue was employed ( Pavani et al., 2019 ). When measuring executive attention with a flanker task, no differences were found between deaf children (mostly speaking with CI) and hearing children ( Daza and Phillips-Silver, 2013 ; Daza González et al., 2021 ) except for Merchán et al. (2022) who observed poorer performance in deaf children. Dye and Hauser (2014) , examining the effect of distractors on a central target with a focus on the difference in performance on two CPTs, found that deaf signers without CI showed poorer performance than their full hearing counterparts.

4 Discussion

4.1 current frequency of studies and tasks used.

As observed, there exist notable gaps in our understanding of the visual attention network in deaf individuals, with research focusing on different functions depending on the age of the participants. While tonic alerting has been extensively researched in both adult and youth deaf populations, primarily through CPTs, the exploration of phasic alerting remains scarce in both groups. Notably, only one study in adults has investigated phasic alerting, emerging as an unexpected result from a cost and benefit paradigm measuring orienting behavior ( Prasad et al., 2022 ).

Similarly, concerning the orienting network, while there is a wide range of research on exogenous orienting in deaf adults, few studies have tested these differences in deaf children ( Daza and Phillips-Silver, 2013 ). Moreover, endogenous attention has been underexplored in both age groups.

Regarding executive attention, there appears to be a more balanced interest across developmental stages, primarily through flanker tasks in children and a broader range of conflict tasks in deaf adults. This is likely due to the fact that flanker tasks have been previously studied in deaf adults prior to the scope of this review ( Sladen et al., 2005 ; Dye et al., 2009 ).

From these observations, it becomes evident that there is a critical need to delve deeper into the exploration of phasic alerting and endogenous orienting of attention, particularly in deaf and hard of hearing children. This need arises from the potential existence of adaptive developmental aspects in visual attention that warrant further investigation.

4.2 Results of comparisons between deaf and hearing adults

The results in deaf adults seem to indicate a deficit in the tonic alerting network, which can be explained by several hypotheses. One possibility is that deaf individuals have difficulties in sustaining attention over time, possibly due to a more rapid depletion of attentional resources. To test this hypothesis, investigating how performance changes over the course of a task could provide insights into whether there is a faster decline in performance or a general difficulty in executing the task. While Hoffman et al. (2018) attempted to analyse this aspect, they focused exclusively on children, which will be discussed below. Another hypothesis emerges from the division of labor perspective, which supports the deficit view. According to this notion, the observed results may be due to the need for deaf individuals to rely on vision to simultaneously monitor their environment and focus on a specific task. This dual demand on attentional resources might limit the resources available for performing visual tasks such as the CPT ( Smith et al., 1998 ; Quittner et al., 2004 ).

Normally, phasic alerting is primarily dependent on the auditory system. Therefore, in adults, it would be reasonable to expect that adaptive mechanisms could lead to a heightened state of alert generated by visual cues, as demonstrated in the experiment conducted by Prasad et al. (2022) .

The overall advantage observed in spatial exogenous orienting in deaf adults appears to be attributable to covert orienting rather than overt orienting/ eye movements ( Prasad et al., 2015 ; Brazão et al., 2021 ; Prasad et al., 2022 ). This supports the notion of an adaptive alteration in the visual attention system in deaf individuals. This adaptation enables them to monitor the environment since they are able to efficiently shift their attentional focus across the visual field towards important stimuli and also disengage from them more rapidly.

The mechanisms governing orienting of attention or eye movements have been shown to be more dependent on endogenous attention, which could explain why the differences between deaf and full hearing individuals do not extend to the results of these tasks ( Zangrossi et al., 2021 ; Celli et al., 2022 ). Endogenous orienting does not differ between deaf and typical hearing adults, whether measured by visual search ( Heimler et al., 2015a ) or spatial orienting paradigms using central cues ( Heimler et al., 2015b ; Bonmassar et al., 2021 ; Li et al., 2022 ). One explanation for this result is that endogenous orienting of attention requires voluntary control of attention (top-down), while exogenous attention is an involuntary mechanism (bottom-up), as some results indicated that deaf individuals could have worse executive control, possibly explaining the lack of differences in these tasks ( Li et al., 2022 ). However, as we have found in this review, deficits in executive control are not common in adults or native signers, contrary to the results found in orienting. Another possible explanation for this discrepancy is that this function does not show differences since it is not inherently adaptative. In contrast, the improvements observed in exogenous orienting could stem from the need to monitor environmental changes using only the visual system, without the support of the auditory system. On the other hand, attention shifts due to endogenous attention could be distracting for deaf individuals required to maintain a strong focus on hands and facial expressions during conversations.

Regarding executive function, no differences were found in a typical flanker task ( Holmer et al., 2020 ). However, when distractors were placed in the periphery instead of the centre, deaf individuals showed poorer performance compared to their hearing peers ( Chen et al., 2010 ). These contradictory results seem to support the hypothesis that the observed performance deficits in conflict tasks with central targets may not necessarily be due to deficits in executive attention. Instead, these findings could be due to the further allocation of attentional resources towards distractors in comparison to hearing individuals. This explanation is further supported when these results are compared to those of the UFOV tasks, where both targets and distractors are located in the periphery. In these tasks, deaf individuals tend to have an advantage ( Dye et al., 2016 ; Samar and Berger, 2017 ). However, the findings of Hauthal et al. (2012) could indicate an adaptive change specifically in the processing of faces. These results suggest that the performance of signers without CI in executive attention tasks depends on the position of the target, which can be explained by the further allocation of attention towards the periphery. An alternative interpretation of these findings is that deaf adults may develop an advantage in the ventral attention network (VAN). The VAN is responsible for reflexive bottom-up attentional mechanisms and has been associated with exogenous orienting and phasic alerting This could potentially explain the observed benefits in both functions among deaf adults. In contrast, the dorsal attention network (DAN) governs voluntary or top-down attentional mechanisms and has been linked to endogenous orienting, tonic alerting, and executive functioning ( Corbetta and Shulman, 2002 ; Rueda et al., 2023 ). Apart from tonic alerting, it appears that deaf adults may not experience performance deficits relative to typical hearing controls in this pathway.

4.3 Findings of comparisons between deaf and hearing children

In children, the differences between deaf and typical hearing individuals vary according to age, suggesting that middle childhood is an important period of development for visual attention. Our review found that deaf children show worse scores in CPTs, which is argued as being indicative of a deficit in tonic alerting. However, contrary to this notion, Hoffman et al. (2018) found no differences in performance block by block between deaf and hearing children. This suggests that tonic alerting or vigilance may not be affected, but the difference in performance is due to the division of labor, as mentioned previously. Furthermore, the poor performance during these tasks was characterized by high commission errors ( Yucel and Derim, 2008 ; Hoffman et al., 2018 ), which could be interpreted as poor inhibition or impulsivity. These findings have been replicated with other paradigms that measure response inhibition, such as the Go/No Go or Simon tasks ( Figueras et al., 2008 ; Botting et al., 2017 ; Hall et al., 2018 ).

The results reported by Daza and Phillips-Silver (2013) , indicating higher phasic alerting and faster exogenous orienting, could potentially suggest a benefit due to the lack of auditory stimulation. However, these results have not been directly compared with those of hearing children. We must also consider that the differences in endogenous attention found by Pavani et al. (2019) can only be interpreted in the context of gaze cues, since there is evidence that other (non-gaze) directional cues rely on different processes ( Heimler et al., 2015b ). Consequently, there is insufficient experimental data on orienting in deaf children in comparison to their hearing counterparts, which prevents us from drawing any firm conclusions in this regard.

Concerning executive attention, discrepancies between the results of Dye and Hauser (2014) and Merchán et al. (2022) and those of Daza González et al. (2021) could be due to differences in the sample, specifically in terms of age, since the latter study focused on children aged 9 to 10 years. As observed in adults, deaf children show no difference in UFOV task performance between the ages of 7 and 10 years. In fact, their performance surpasses that of their hearing peers between the ages of 11 and 17 ( Dye et al., 2009 ; Dye and Bavelier, 2010 ). This discrepancy in performance might manifest as a reduced ability to ignore distractors when they are at the periphery and the target is in the centre of the visual field. Notably, this difference disappears when the target is also positioned in the periphery, supporting the hypothesis that attentional resources are allocated toward the periphery.

In general, we can conclude that, as expected, the findings have revealed improved performance of deaf individuals in tasks related to covert exogenous orienting, with limited impact on endogenous orienting in adults. However, deaf individuals show poorer execution of tasks involving tonic alertness and executive attention, except when the target is presented peripherally. These results are consistent with much of the clinical literature in deaf individuals ( Barker et al., 2009 ) and support the integrative hypothesis suggesting a deficiency in the temporal distribution of attention and an enhancement in spatial distribution ( Dye and Bavelier, 2010 ). Finally, from the perspective of the attention network model, our study highlights the need to further explore phasic alerting. Currently, there is a gap in research exploring differences in exogenous and endogenous orienting between deaf and full hearing children and a lack of studies investigating the endogenous orienting network in deaf adults.

4.4 Development of attention network functions in deaf children

Regarding our objective of characterizing the development of attentional networks in middle childhood within the deaf population, several conclusions can be drawn. However, we must consider the need for further research in this area, particularly through longitudinal studies.

Our findings indicate that tonic alertness continues to develop from ages 6 to 13 in both deaf and typical hearing children ( Dye and Hauser, 2014 ; Dye and Terhune-Cotter, 2023 ). This aligns with previous research on typical hearing children using the same task, which showed a specific development ceiling at 10 years old ( Betts et al., 2006 ). However, it appears that deaf individuals do not reach the levels observed in typical hearing adults, at least those who are not native signers ( Bharadwaj et al., 2020 ).

The elemental operations of moving and engaging improve between the ages of 6 and 7 in deaf children ( Daza and Phillips-Silver, 2013 ). In comparison to hearing children, our results suggest that orienting networks continue to develop during middle childhood in deaf individuals, whereas in their hearing counterparts, this development tends to plateau at around 6 years old ( Rueda et al., 2004 ; Pozuelos et al., 2014 ; Federico et al., 2017 ). Notably, this development in deaf individuals appears to extend into adulthood, providing them with an advantage over typical hearing adults. Interestingly, when measuring electrophysiological brain activity through evoked potentials, improvements in visual attention related to saliency processing and orienting of attention have been observed as early as 3 years of age. These measures demonstrate improvement during the early years in deaf children, indicating early and differential development of these components of attention ( Campbell and Sharma, 2016 ; de Schonen et al., 2018 ; Gabr et al., 2022 ; Corina et al., 2024 ).

Finally, executive attention seems to improve between 7 and 9 years of age in deaf children. Dye and Hauser (2014) found that deaf signers without CI reach the same levels of performance between 9 and 13 years old. However, Daza González et al. (2021) found no differences among children aged 9–10, while Merchán et al. (2022) observed worse performance in a sample of 7–10 years old. These findings are consistent with those reported in studies of typical hearing children, suggesting that difficulties found in this aspect of the attention network cannot be solely attributed to late development ( Rueda et al., 2004 ; Pozuelos et al., 2014 ; Federico et al., 2017 ). When comparing deaf and hearing adults, it is plausible that deaf individuals continue to show development in exogenous orienting during early childhood, eventually achieving better performance than their hearing counterparts ( Bottari et al., 2012 ; Prasad et al., 2015 ). In adulthood, deaf signers without CI reach similar levels in executive attention when central targets are present ( Chen et al., 2010 ; Holmer et al., 2020 ). However, differences in tonic alertness may persist into adulthood ( Parasnis et al., 2003 ; Kronenberger et al., 2013 ).

4.5 Effects of the communication system and the use of cochlear implants

In most studies, the use of sign language is associated with the absence of a CI. It is important to recognize the clear distinction between culturally deaf people who communicate mainly in sign language within deaf communities and those who have received CI along with speech therapy. The latter group has experienced some level of auditory input and uses a language that is less reliant on visual cues.

In adults, there are no studies on tonic alertness involving deaf signers without CI. However, age at CI implantation does not seem to have an impact on CPT performance ( Kronenberger et al., 2013 ; Bharadwaj et al., 2020 ). While no differences were observed between deaf signers without CI and full hearing children ( Dye and Hauser, 2014 ), differences have been found in oral-speaking deaf children with CI ( Yucel and Derim, 2008 ; Hoffman et al., 2018 ). Additionally, Daza and Phillips-Silver (2013) found differences in tonic alertness between oral speaking deaf children with CI and deaf signers without CI in favor of the former. Dye and Terhune-Cotter (2023) found that while the English language was a strong predictor of better sustained attention, ASL proficiency was a more accurate predictor of response inhibition.

Generally speaking, these findings suggest a consistent trend toward poorer performance on tonic alerting tasks in oral speaking deaf individuals. Notably, the lack of an effect of age of implantation in adults raises the possibility that early language acquisition does not influence these outcomes. Regarding exogenous orienting, it is evident that elementary operations of orienting such as moving and engaging are enhanced in deaf signers without CI compared to oral speaking deaf individuals with CI ( Daza and Phillips-Silver, 2013 ). Additionally, the advantage observed in executive attention towards peripheral targets in adults appears to be more prevalent among deaf signers without CI ( Samar and Berger, 2017 ), while in children these improvements have also been found in deaf signers without CI ( Dye et al., 2009 ).

These findings align with the main hypothesis put forward to explain differences in performance on tasks that measure different executive functions in deaf people and could also be applied to these results, that is, worse performance can be attributed to late acquisition of language ( Hall et al., 2017 , 2018 ; Merchán et al., 2022 ). This explanation has commonly been invoked when attempting to explain performance on executive function tasks, but as observed in this review, tonic alertness also appears to be affected. However, an adaptive form of development is evident when executive attention is directed toward the periphery in deaf signers without CI who lack auditory stimulation and have delayed acquisition of language ( Dye et al., 2009 ; Samar and Berger, 2017 ). Unfortunately, there is insufficient evidence to conclusively establish the impact of these variables on phasic alertness, endogenous orienting, and executive attention.

5 Conclusion

In summary, there are notable gaps in the literature regarding the functions of visual attention networks, specifically in the alerting network functions in adults, phasic alerting, and both orienting networks in children. Current evidence suggests that deaf adults show poorer performance during CPTs, but this might not necessarily be attributed to deficits in tonic alerting. Phasic alerting, on the other hand, appears to confer advantages in deaf adults. Exogenous orienting shows enhancements, whereas endogenous orienting does not. Additionally, differences in executive attention are evident, particularly depending on the peripheral placement of the distractors. In children, the evidence reveals similar patterns of results, with the exception that difficulties in executive attention are observed before the ages of 9 or 10.

Regarding individual differences in language delay and the use of CI, it seems that benefits in exogenous orienting are more frequent in deaf individuals without CI and users of sign language while language abilities appear to be a good predictor of difficulties in executive attention. This understanding contributes to the growing body of knowledge in the field, emphasizing the need for further research to bridge the identified gaps and refine our comprehension of the intricate development of visual attention networks in the deaf population.

Data availability statement

The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author.

Author contributions

NG: Writing – original draft, Methodology, Investigation. JP-S: Supervision, Conceptualization, Writing – review & editing. MD: Writing – original draft, Supervision, Writing – review & editing, Funding acquisition, Conceptualization.

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. This research was supported by a grant PID2019-111454RB-I00/AEI/10.13039/501100011033 from Spanish Ministry of Science and Innovation—Spanish State Research Agency, to the last author.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Publisher’s note

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Keywords: deaf, children, attention, hearing, orienting, review methodology, investigation

Citation: Gioiosa Maurno N, Phillips-Silver J and Daza González MT (2024) Research of visual attention networks in deaf individuals: a systematic review. Front. Psychol . 15:1369941. doi: 10.3389/fpsyg.2024.1369941

Received: 13 January 2024; Accepted: 22 April 2024; Published: 09 May 2024.

Reviewed by:

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*Correspondence: María Teresa Daza González, [email protected]

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