The distractor frequency effect in the colour-naming Stroop task: An overt naming event-related potential study

We used the event-related potential (ERP) approach to track the time course of the distractor frequency effect in the colour-naming Stroop task, i.e. the longer naming latency when to-be-ignored words are low frequency rather than high-frequency words. ERPs elicited by coloured words were influenced by distractor frequency in 160–220 ms and 300–400 ms time windows. In a Stroop variant of the colour-naming task, ERPs elicited by coloured words were affected by colour/word congruency in 300–400 ms and 500–600 ms time windows. Temporal and polarity features of distractor frequency and Stroop ERP responses suggest that the distractor frequency effect in the colour-naming Stroop task is characterised by at least two temporally and functionally distinguishable ERP effects: one early effect that we interpret as reflecting the processing of the distractor words and one mid-latency effect reflecting suppression of the distractor word.