Both task-irrelevant and task-relevant information trigger reactive conflict adaptation in the item-specific proportion-congruent paradigm.

Adapting attention flexibly is a fundamental ability of the human control system. In the color-word Stroop task, for example, congruency effects are typically smaller for colors and words that appear mainly in incongruent stimuli (mostly-incongruent items) than for colors and words that appear mainly in congruent stimuli (mostly-congruent items). At least part of this item-specific proportion-congruent (ISPC) effect is due to a process of reactive conflict adaptation that affords higher selectivity (i.e., more efficient selection of task-relevant information) when a specific stimulus is presented that is frequently associated in the experiment with conflicting task-irrelevant information. What is unclear, however, is whether, normally, this stimulus-specific adaptation is triggered by the task-relevant component, the task-irrelevant component, or both components of the stimulus. In two experiments, using modified color-word (Experiment 1) and spatial (Experiment 2) Stroop tasks that allowed task-relevant and task-irrelevant triggering processes to be dissociated, we found that the two processes have approximately equivalent impacts. Because these results were obtained in experiments imposing no limitations on the processes potentially contributing to the ISPC effect, these results challenge claims that the ISPC effect involves conflict-adaptation processes only in special situations. The ISPC effect may involve conflict-adaptation processes in most situations, with both task-relevant and task-irrelevant information triggering such processes.