As expected based on the Gratton effect, there was a significant previous × current conflict interaction (repeated-measures ANOVA, F1,14 = 14.29, p = 0.002). Reaction times were longest on cI trials, shortest on cC trials, and in between during iI and iC trials (Figure 1A). To examine the effects of stimulus luminance on reaction times, we correlated, for each subject, luminance and reaction time separately for each condition (Figure 1B), and then tested those correlation coefficients across subjects. Correlation coefficients were significantly greater than zero in all conditions except for cC (p-values: 0.53, <0.001, 0.002, 0.033 for cC, cI, iC, and iI conditions), although the interaction term in a previous × current conflict repeated-measures ANOVA was not significant (F1,14 = 0.59). These results indicate that stimulus luminance affected subjects’ performance only when the current or previous trial contained conflict.
