Abstract:
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.
