Methodological considerations in cognitive neuroscience: A scoping review of fNIRS applications with the Stroop task

Functional near-infrared spectroscopy (fNIRS) has emerged as a valuable technique for studying cognitive neuroscience, with the Stroop test being a predominant paradigm. We conducted a scoping review of 133 fNIRS-Stroop studies published over the past 20 years to map methodological trends. Most studies used a block design and lacked sufficient control conditions to analyze the Stroop effect. Although the sample sizes increased in recent years, the majority had an inadequate number of participants, especially for studies comparing two or more samples. Nearly all reported only oxygenated hemoglobin (oxy-Hb), while deoxygenated hemoglobin (deoxy-Hb) analyses appeared mainly in event-related designs. We observed substantial heterogeneity in Stroop variants and control tasks, hindering cross-study comparisons. Although the Stroop test is well suited to fNIRS, few studies adopted designs or theoretical frameworks capable of isolating specific cognitive processes or underlying neural circuits; instead, many focused on group differences or intervention effects. This review underscores the necessity for greater methodological standardization in future research to improve the interpretation of the Stroop test within the domain of cognitive neuroscience.