The "red-alert" effect in visual search: evidence from human electrophysiology.

Participants had to determine the orientation of a segment inside a target color circle among other gray distractor circles. The target circle was either red or green and was accompanied in the display by a distractor in the other color. To dissociate event-related potentials of target and distractor processing, one of them was on the vertical meridian and the other in a lateral position. In Experiment 1, the target color was indicated on a per-trial basis and, in Experiment 2, on a per-block basis. The results revealed the N2pc elicited by red targets had an earlier latency relative to the N2pc elicited by green targets. Contralateral responses of positive polarity linked to distractor inhibition were found only with red lateral distractors. The results suggest that the choice of colors to distinguish targets from distractors may play a role in visual search performance and in the functional characterization of event-related lateralizations.