Physiological measures of attention: NIRS

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Systematic literature review

To uncover relevant research using NIRS to study the atypical and typical development of attention, a systematic literature review was conducted. A systematic literature review is useful as a preliminary mapping and investigation of a specific research question. It includes a precise delineation of a replicable search strategy characterized by clearly stated inclusion and exclusion criteria, a transparent data extraction and synthesization process, and a quality assessment protocol which may rely on multiple raters (Jesson, Matheson & Lacey, 2011; Cronin, Ryan, & Coughlan, 2008).

Search procedure

The search involved in this systematic review took place in March of 2018 using databases ERIC, PsycINFO, Pubmed and Medline. Databases and search terms were chosen in consultation with a librarian. In PsycINFO and ERIC, a search using the thesaurus function was performed in combination with a free text search. In Pubmed and Medline, free search terms in the advance option were used. Search terms varied slightly across the databases as relevant or suggested related terms differed across the databases. Generally, there were three “MeSh” categories or overarching terms included in each database: “attention”, “functional near-infrared spectroscopy”, and “children OR adolescents.” As mentioned, related or suggested terms varied, but generally included a number of related terms in each of these three overarching categories. Please see Appendix A for the exact terms used in the search protocol. The search yielded 77 results in PubMed, 90 results in Medline, 92 results in PsycInfo and 12 results in ERIC (an educational database). As such, the initial search yielded a total of 271 articles across all four databases. Additionally, after looking at reference lists of previous literature reviews on related topics, 1 additional study was identified and subsequently added.

Inclusion/exclusion criteria

Inclusion and exclusion criteria were developed to determine which studies to include in the review. To ensure the focus on attention in children with atypical development, only studies which included both an atypically developing and typically developing group were considered.
Additionally, NIRS needed to analyze brain activity, not some other physiological measure such as heart rate. There were no limitations for the time frame, as the technology for NIRS has emerged fairly recently (Vanderwert & Nelson, 2014). The extraction protocol with inclusion and exclusion criteria is shown in Table 1.

Screening procedure – title and abstract level

Articles collected in PsycINFO, Pubmed, Medline, and ERIC were first screened at the title level. After title review of the 90 articles on Medline, 19 were carried forward for abstract review. Next, after a title review of the 92 articles on PsycInfo and after manually removing duplicates, 12 articles were left. Next, after reviewing 12 studies on ERIC, 3 were carried forward for the abstract review. Finally, after screening 77 titles on Pubmed and after duplicates were removed, 19 were brought forward for abstract review. Overall, of the initial 271 studies, 218 studies were excluded based on the above criteria based on titles alone. Generally, studies were excluded for being drug trials, measuring some other cognitive function through NIRS, or including adults. As such, 53 studies were carried forward for abstract review based on the above criteria, and 1 additional study was identified through searching citation lists in relevant past reviews. The screening process is pictured in a flow chart in Appendix B.
For the abstract screening procedure, two raters separately reviewed each of the 54 abstracts to ensure they adhered to the above inclusion criteria. Prior to speaking, both raters separately noted down whether or not each of the studies should be carried forward for full text review based on their interpretation of the inclusion/exclusion criteria, and then compared these notes afterwards. Raters agreed upon 20 articles to be carried forward for review, with 2 out of the 54 articles flagged by both inter-raters for further discussion, therefore yielding an 100% consensus rate. After this discussion, 2 articles were excluded for not using NIRS to measure a dimension of attention. After this process, both raters unanimously recommended 20 articles to be carried forward for full text review.

Selection process – full text 

Inclusion and exclusion criteria were again applied to the entire article in the full-text screening process with two raters. There was a particular focus on the methods section of each article. Of the 20 articles reviewed, 7 were not carried forward for the data extraction process. 4 articles did not have full texts available online; however, three other articles were flagged by both raters as not adhering to the exclusion/inclusion criteria again showing an 100% consensus rate. There was 1 article which focused on short-term memory which was deemed outside of the attention construct; and 2 articles which did not include relevant details related to NIRS data (number of channels, regions of interest). As such, 13 articles were left over for data extraction (see Appendix B for flow chart).

Data extraction and quality assessment

Data extraction was performed using the protocol shown in Appendix C. Extracted information includes title, author(s)/date, name of journal, country, aim, research questions if applicable, study design, information about the sample (age, total participating N, classification of atypical development, attention dimension, behavioural stimuli/task (specific test, results if applicable), NIRS information (channels, brain regions, oxy-Hb/deoxy-Hb), results, and any noteworthy or incongruent findings or limitations. Two raters independently reviewed the quality of 2 articles and after agreement was found, one reviewer assessed the remaining 11 articles. Quality assessment was performed using the CASP checklist for quantitative research and in particular for case-controlled studies (CASP, 2018, see Appendix D). Good quality denotes >70% of quality fulfilled, moderate quality is >60% fulfilled, and low quality <60% fulfilled. Answers “yes” fulfilled criteria, while “no” or “can’t tell” did not. Importantly, some questions in the CASP (2018) checklist included whether or not the results were significant but did not a power calculation or number of participations (N) which presents a limitation. Many of the studies were exploratory, and therefore a lower N and insignificant results do not indicate an incorrect hypothesis. Some NIRS-specific questions were added to the checklist.

Data analysis

Data were extracted and analyzed qualitatively. An identification number was given to each study. First, in the qualitative analysis, overall general information of the studies was reported and formed into key points in order to form a preliminary understanding of the general rationale for using NIRS in the research of attention in atypical development. To answer research question 1 related to evidence for functional differences in brain regions associated with attention in children with typical/atypical development, results were analyzed, grouped and subsequently reported. To answer research question 2, behavioural measures results and NIRS data were extracted into a table to compare the results side by side. To answer research question 3, themes related to theoretical basis of attention or behavioural implications throughout each article were examined to determine whether they included the topics of interest. Quantitative meta-analysis was not possible as there were no consistent measures used (oxy-Hb and deoxy-Hb, differing number of channels/analysis methods, and different brain regions reported).

1 Background and Rationale
1.1 Introduction
1.2 Defining attention
1.3 Theories of attention
1.4 Attention and atypical development
1.5 Attention and engagement
1.6 Behavioural measures of attention
1.7 Physiological measures of attention: NIRS
1.8 Methodological challenges of NIRS
1.9 Past literature reviews of NIRS
1.10 Rationale of the present review
 2 Purpose of the systematic review and research questions 
3 Method
3.1 Systematic literature review
3.2 Search procedure
3.3 Inclusion/exclusion criteria
3.4 Screening procedure – title and abstract level
3.5 Selection process – full text
3.6 Data extraction and quality assessment
3.7 Data analysis
4 Results 
4.1 Overview of studies
4.2 Main NIRS findings
4.3 Behavioural measures results and NIRS findings
4.4 Theoretical basis and behavioural implications
5 Discussion
5.1 Evidence of functional differences
5.2 Behavioural measures results and NIRS measures
5.3 Theoretical basis and behavioural implications
5.4 Suggestions for future research
5.5 Limitations of the study
6 Conclusion 
7 References
Functional Near-Infrared 
Spectroscopy for the Study of 
Attention in Children with Atypical Development

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