An ERP study of sustained spatial attention to stimulus eccentricity

Effects of attention on event-related brain potentials (ERPs) were measured when subjects kept sustained attention focused on ring-shaped regions of v isual space to detect infrequently presented targets at a given eccentricit y. In line with a previous study that employed a trial-by-trial cueing para digm, no modulations of sensory-evoked P1 and N1 components were found. Thi s suggests that attentional selectivity in complex spatial selection tasks is primarily located at post-perceptual processing levels. Enhanced negativ ities for attended as compared to unattended stimuli were present between 2 20 and 380 ms post-stimulus and were followed by an enlarged positivity for attended stimuli in the P3 time range. These effects reflected the distrib ution of attention in visual space, in part consistent with 'attentional gr adient' and 'zoom-lens' models. However, ERPs also suggested the presence o f selective mechanisms that exclude irrelevant stimuli located between two simultaneously attended areas. (C) 2000 Elsevier Science B.V. All rights re served.