Dissociating adaptation to word-specific and color-specific conflict frequency in the Stroop task

In the Stroop task, congruency effects are typically larger for color words presented mainly in their congruent color than for color words presented mainly in incongruent colors. However, the nature of this item-specific proportion congruent (ISPC) effect is debated: It might be produced by either conflict-adaptation processes (e.g., focus attention to task-relevant information when the word BLUE appears) and/or a more general contingency-learning process (e.g., anticipate a green response when the word BLUE appears). We re-examined the role of conflict-adaptation processes in this paradigm in two experiments. In both experiments, a conflict-adaptation effect emerged on stimuli matched on contingency. Further, in Experiment 2, we found separate effects of adaptation to the frequency of conflict specific to the color and word dimensions of individual stimuli. These results challenge the contingency-learning account of the ISPC effect and suggest that conflict-adaptation processes in this paradigm may depend on both task-relevant and task- irrelevant information.