There is current debate as to whether spatial attention can modulate V1 activity during the initial wave of visual processing. Research on this topic has focused on the event-related potential (ERP) C1 component, which primarily reflects activity in V1. The purpose of the present selective review was to compare experimental parameters across spatial attention studies to determine whether certain stimulus, task, or analysis conditions were more likely to produce significant C1 attention effects. Specifically, C1 attention effects were evaluated as a function of visual field location, presence or absence of distractors, load (perceptual or attentional), cue type (endogenous or exogenous), and electrode location. As the C1 component has its peak magnitude at midline parietal-occipital electrodes, only studies that measured C1 attention effects at these electrode locations were considered. Furthermore, only studies that manipulated spatial attention, and no other factors, were considered. The current analysis indicated that to maximize sensitivity to C1 attention effects, stimuli should be in the upper visual field, there should be distractors, conditions should be high perceptual or attentional load, there should be exogenous cuing, and effects should be measured at midline parietal-occipital electrodes POz, Pz, and CPz.
Keywords: Attention; C1; ERP; P1; V1; spatial attention.