Proportion Compatibility/Congruency Effects on Event-Related Potential Components Depend on Task Characteristics in the Flanker and Stroop Tasks.

Previous studies modified the flanker task to include surrounding- or central-deviant stimuli, and showed that visual mismatch negativity (VMMN) for surrounding-deviant stimuli was reduced in the mostly incompatible (MI) blocks compared with the mostly compatible (MC) blocks, whereas VMMN for central-deviant stimuli did not differ between MI and MC blocks. This study, which reanalyzed data from previous studies, revealed that P3 for both surrounding- and central-deviant stimuli was modulated by proportion deviance; however, this modulation did not differ between MI and MC blocks. Additionally, new data were collected using a Stroop task modified to include word- or color-deviant stimuli. The results indicated that VMMN was elicited by word-deviant stimuli but was not modulated by proportion congruency, whereas VMMN was not elicited by color-deviant stimuli. In contrast, for both word- and color-deviant stimuli, late event-related potential components were modulated by proportion deviance; this modulation was reduced for word-deviant stimuli and enhanced for color-deviant stimuli in the MI block relative to the MC block. Taken together, proportion compatibility effects were evident in early, but not late, ERP components for irrelevant-dimension stimuli in the flanker task. In contrast, proportion congruency effects were evident in late, but not early, ERP components for both irrelevant- and relevant-dimension stimuli in the Stroop task. These findings suggest that proportion compatibility/congruency effects on irrelevant and relevant processing may depend on task characteristics, although this interpretation remains tentative.