Abstract:
A typical visual scene includes many objects, but we are only aware of a small subset at any given time. In order to function in the world in spite of this limitation, we must selectively attend to goal-relevant objects while ignoring or suppressing irrelevant information. Previous research has used electroencephalography (EEG) to isolate brain potentials related to the selection of visual “targets”, the suppression of “distractors”, and processing in visual short term memory. Target selection is associated with the N2pc component of the visual evoked potential. N2pc typically occurs 180-250ms post-stimulus and manifests as increased negative voltage at posterior scalp electrodes contralateral to visual targets. A later potential with a more temporal scalp distribution, the Ptc, has been associated with the suppression of distractors, and a third final component, the SPCN, is believed to index visual short term memory processing. Here, we employed high-density EEG to provide evidence for the dissociation of N2pc, Ptc, and SPCN as well as estimates of their likely cortical generators. Participants responded to the orientation of a coloured target in amongst a circle of gray fillers while ignoring a coloured distractor. In half of the trials the target was lateralised while the distractor was on the midline, in the remaining trials this was reversed. This allowed us to dissociate the effects of targets and distractors. Our data show that the neural generators of the N2pc and Ptc are spatially dissociable, while the SPCN co-localises with the N2pc. This confirms previous indications that the N2pc, Ptc, and SPCN are functionally independent components of the VEP which index attentional selection, distractor suppression, and visual short term memory respectively.