abstract
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The Stroop effect is considered a reliable measure of the contributions of word reading and colour naming processes. Changes in the size of the Stroop effect suggest modulations in the relative contributions of the two processes. Furthermore, item specific proportion congruent (ISPC) differences in the Stroop effect suggests that these modulations are rapid and stimulus driven. Recent behavioural and event-related potential (ERP) findings in a global/local task support the hypothesis that modulations in control can occur very early in visual processing. The present study extended the application of ERP methods to examine item-specific proportion congruency effects in the Stroop task. Findings from the present study are consistent with previous studies and observable ERP differences were recorded at the N1 component as early as 140 ms at site O1. These findings suggest that modulations in control can occur rapidly upon stimulus onset However a surprising finding at site Oz suggests that itemfrequency also plays a role in affecting response selection. The latency and location of this effect are similar to those reported by Shedden et al. (2009) suggesting that item specific effects occur as early as 100 ms. As well, this is the first study to report a combined influence of a simple associative learning mechanism and rapid, contextually driven control processes.