Various models of the Stroop task suggest that proactive task control adaptation accounts for the modulation of task conflict in different conditions of the Stroop task, for example, when task conflict is very frequent or very infrequent. Other researchers have argued that a contingency learning of colour-word associations is the main contributor to the modulations of the Stroop effect. In this work, we constructed a design that controls for confounds that are suspected to rule out the role of control adaptation in the Stroop task. We focused on one type of conflict-task conflict and tested whether colour-naming of neutral-words (where task conflict is present) differed from colour-naming of neutral-symbols (where task conflict is not present) in four different conditions: mostly words-congruent, mostly words-incongruent, mostly words-neutral, or mostly non-words-shape. Importantly, the conditions used for the task conflict marker were identical in all four conditions. We found that the marker of task conflict (reaction time [RT] for neutral-words > RT for neutral-symbols) was significant in the mostly non-words-shape condition, where proactive task control is relaxed, but not in the mostly words conditions, where proactive task control is activated, with no difference between these three words conditions. These findings suggest that control adaptation is the main contributor to the modulations of the Stroop effect. The relevance of the results to the current literature is discussed and the results are explained in light of the proactive control-task conflict (PC-TC) model.
Keywords: Stroop; Task conflict; contingency learning; executive functions; proactive control.