Conflict adaptation in a confound-minimized face-word Stroop task: Exploration of parameter space for studying neural mechanisms

Conflict adaptation refers to the adjustment of cognitive control to reduce interference on subsequent trials. Its neural mechanisms are often studied by assessing the congruence sequence effect (CSE) in face–word Stroop tasks during neuroimaging. The present study aimed to address two key methodological issues when using standard response conflict tasks in fMRI settings: Ensuring the involvement of cognitive control in the CSE and demonstrating its temporal stability across varying inter-trial intervals. In a set of five experiments, using an adapted version of the face–word Stroop task, participants performed either a gender categorization (Experiment 3) or responded to the learned identity of four faces while ignoring the printed name (all other experiments). We specifically incorporated recent advancements in confound minimization to exclude effects of feature integration and contingency learning, included a priming component to further increase the involvement of cognitive control, and used a variable range of inter-trial intervals to test for potential applicability in fMRI research. Although a robust Stroop effect was consistently observed in all experiments, a strong CSE emerged specifically in the gender categorization task. In the confound-minimized face–word Stroop variant, a significant CSE occurred only under specific conditions (e.g., sufficiently long target presentation, bi-manual responses) and was accompanied by substantial inter-individual variability. Therefore, while we observed a reliable CSE in a confound-minimized face–word Stroop task with long inter-trial intervals, the increased methodological rigor that improves precision and interpretability also adds complexity and yields smaller and more variable effects. This trade-off constitutes an important consideration for future fMRI adaptations of the Stroop task seeking to investigate the neural mechanisms underlying the CSE.