Abstract
Several recent behavioral studies have demonstrated that central nonpredictive arrows trigger reflexive shifts of spatial attention (e.g., Tipples, 2002; Ristic et al, 2002; Gibson & Bryant, 2005) as indexed by response time (RT) facilitation for targets occurring at cued locations. Despite the robustness of this behavioral effect, it is still unclear whether the reported RT effect reflects attentional modulation of early cortical visual processing typically associated with reflexive orienting to visual events measured with event-related potentials (ERP, e.g., Mangun & Hillyard, 1987; 1990; Hopfinger & Mangun, 1998). This amplification, or sensory gain, is often observed as an increased amplitude of the first large positive deflection in the sensory-evoked ERP, known as the P1. Here, we investigated whether reflexive orienting in response to a nonpredictive arrow resulted in an enhancement of the P1 component. Observers detected a peripheral target that occurred after the presentation of a central nonpredictive arrow cue. Replicating previous behavioral results, RT facilitation was observed for cued relative to uncued target locations. Importantly, at electrode sites contralateral to the target location, the mean amplitude of the P1 was also larger for cued targets relative to uncued targets. This result indicates that central uninformative arrow direction causes increased sensory processing in extrastriate visual areas. As such, these data add to the growing body of evidence indicating that the behavioral facilitation observed in response to central nonpredictive arrow cues reflects reflexive shifts of covert spatial attention.