An ERP study of the temporal course of the Stroop color-word interference effect

The electrophysiological correlates of the Stroop color-word interference e ffect were studied in eight healthy subjects using high-density Event-Relat ed Potentials (ERPs). Three response modalities were compared: Overt Verbal , Covert Verbal, and Manual. Both Overt Verbal and Manual versions of the S troop yielded robust Stroop color-word interference as indexed by longer RT for incongruent than congruent color words. The Incongruent vs Congruent E RP difference wave presented two effects. A first effect was a medial dorsa l negativity between 350-500 ms post-stimulus (peak at 410 ms). This effect had a significantly different scalp distribution in the Verbal and Manual Stroop versions, with an anterior-medial focus for overt or covert speech, and a broader medial-dorsal distribution for the manual task. Dipole source analysis suggested two independent generators in anterior cingulate cortex . Later on in time, a prolonged positivity developed between 500-800 ms pos t-stimulus over left superior temporo-parietal scalp. This effect was prese nt for all the three response modalities. A possible interpretation of thes e results is that Stroop color-word interference first activates anterior c ingulate cortex (350-500 ms post-stimulus), followed by activation of the l eft temporo-parietal cortex, possibly related to the need of additional pro cessing of word meaning. (C) 2000 Elsevier Science Ltd. All rights reserved .