Significant main effects of Previous trial accuracy, F(1, 1969) = 213. 18, p < .001, indicating larger amplitudes following correct responses (M = −1.95 µV) than incorrect responses (M = 0.01 µV) and Current trial type, F(1, 1969) = 12.25, p < .001, indicating larger amplitudes overall on incompatible trials (M = −1.21 µV) than on compatible trials (M = −0.73 µV), were qualified by a Group × Previous trial accuracy × Compatibility interaction, F(2, 1969) = 7.80, p < .001. Planned contrasts showed that, on trials following correct responses, incompatible arrays elicited larger FSW amplitude than compatible arrays for participants in all beverage groups (this effect was marginal in the control group), consistent with the N2 data. However, on trials following errors, only placebo group participants showed a larger FSW on incompatible than compatible trials.
