Contingency learning on the proportional congruency effect of the Stroop task is manifest in deviant processing

ObjectiveThe proportion congruency effect has been reported in interference tasks. The mostly congruent block is the frequent condition, and the mostly incongruent block is the rare condition for congruent stimuli, whereas the mostly congruent block is the rare condition, and the mostly incongruent block is the frequent condition for incongruent stimuli. This study examined the cognitive mechanism underlying the proportion congruency effect in the two-choice Stroop task using event-related potential components related to deviant processing.MethodStimuli were Kanji characters meaning 'red' and 'blue' painted by congruent and incongruent colors. Participants were required to provide a two-choice button-press response corresponding to the colors. The congruent and incongruent stimuli were presented on rare (20%) and frequent (80%) conditions.ResultsN1 was enhanced in the rare condition relative to the frequent condition for both congruent and incongruent stimuli. The results suggested that colors and characters were not processed independently in the N1 time range, which made selective attention to the relevant feature difficult. Posterior negativity from 200 to 250 ms was also different between rare and frequent conditions, indicating the presence of visual mismatch negativity for congruent and incongruent stimuli. It was considered that the distinction between congruent and incongruent stimuli was evident in mostly incongruent blocks, indicating that the selective attention mechanism was not actively engaged.ConclusionThe proportion congruency effect was explained by contingency learning rather than selective attention in the present task. The cognitive mechanisms underlying the proportion congruency effect are reflected by deviant event-related potential components.