When and where perceptual load interacts with voluntary visuospatial attention: An event-related potential and dipole modeling study

Perceptual load is recognized to affect visual selective attention, but at an unknown spatiotemporal locus in the brain. To examine this issue, event-related potentials (ERPs) were recorded while participants performed an orientation discrimination task, under conditions of low or high perceptual load. Participants were required to respond to targets (10% of trials) presented in the attended visual field while ignoring all stimuli in the unattended visual field. The interaction between voluntary attention and perceptual load was significant for the posterior N1 component (190 ms) but not for the earlier C 1 (84 ms) or PI (100 ins) components. This load by attention interaction for N1 was localized to the temporoparietal-occipital (TPO) gyros by dipole modeling analysis. Dipole modeling also showed that a reversed attentional effect in the C I time range was due to ERP overlap from the subsequent attention-sensitive PI component. Results suggest that perceptual load affects voluntary visuospatial attention at an early (but not the earliest) processing stage and that the TPO gyros mediates target selection at the discrimination stage. (c) 2007 Elsevier Inc. All rights reserved.