Cognitive neuroscience with fNIRS has many methodological choices, a scoping review of the use of the Stroop task and fNIRS

Functional near-infrared spectroscopy (fNIRS) has been proposed as a valuable imaging technique for the study of cognitive neuroscience, and the Stroop Test is arguably the most popular paradigm used with fNIRS. To gain insight into the current state of fNIRS utilization, we conducted a scoping review of 133 studies that employed fNIRS in conjunction with the Stroop test. The objective was to gain a comprehensive understanding of the methodological landscape of cognitive neuroscience within the fNIRS literature in the last 20 years. Results were surprising. The sample size has not increased sufficiently over the years, particularly for those studies comparing two or more samples. Most studies employed a block design, lacked sufficient control conditions to analyze the Stroop effect, and reported only a grand average of oxygenated hemoglobin (oxy-Hb) and not deoxygenated hemoglobin (deoxy-Hb). Interestingly, the analysis of the deoxy-Hb signal was considerably more prevalent in studies employing an event-related design. Additionally, there was a considerable degree of heterogeneity in the types of Stroop tests employed and the types of control conditions utilized, which renders comparisons between studies challenging. Although Stroop Test could be hypothetically a reasonable choice for using fNIRS in cognitive neuroscience, few studies employ a test design, study design, or theoretical framework that is sufficient to draw specific conclusions in terms of the cognitive processes involved and the underlying neural circuitry. This is because the majority of studies employ fNIRS and the Stroop test to investigate phenomena other than cognition, such as differences between two populations or changes resulting from an intervention.