Attentional selection and identiWcation of visual objects are reXected by distinct electrophysiological responses

Abstract Lateralised ERP responses were measured over posterior visual brain regions in response to visual search arrays that contained one colour singleton. In the localisa-tion task, responses were determined by the visual hemiWeld where this singleton was presented. In the discrimination task, they were determined by the single-tons ’ shape. While an N2pc component was elicited in an identical fashion in both tasks, a subsequent sustained con-tralateral negativity was consistently present at posterior sites in the discrimination task only. This dissociation dem-onstrates that these two activations reXect distinct visual processing stages. We suggest that while the N2pc reXects the ability of the visual system both to identify and localise a relevant stimulus in the scene, the late sustained activity reXects the subsequent in-depth analysis and identiWcation of these stimuli