AbstractsPsychology

Inconsistent with traditional event-related potential (ERP) studies on feature-based attention, there has been some evidence within the literature to suggest feature-based attention can occur independent of and as early as spatial attention. The present study was composed of two separate experiments designed to examine whether feature-based attention can modulate sensory processing of visual stimuli as early as P1 in the absence of direct stimulus competition. Both experiments required participants to discriminate between two equiprobable stimuli that were presented centrally. Furthermore, task-relevance of stimuli was manipulated in both experiments to examine the effects of task context on early sensory processing of stimulus features. Participants alternated between responding to stimuli of low spatial frequency (one-hand response condition) and responding to stimuli of both low spatial frequency and high spatial frequency (two-hand response condition). As expected, analysis of the ERP data in both experiments indicated stimuli of low spatial frequency were of greater task-relevance for the one-hand response condition (indexed by an enhanced P3). Additional analysis of the ERP data revealed a suppression of early sensory processing for task-irrelevant stimuli (indexed by a reduced P1) during the experiment in which the task was difficult. The results of the study suggest that during a difficult discrimination task, feature-based attention can occur as early as the P1 component and independent of spatial attention in the absence of stimulus competition.