Abstract
Increasing the attentional demands (load) of a visual task leads to neural enhancement of task-relevant stimuli and suppression of irrelevant visual distractors. Here, we examined the spatial dynamics and malleability of such enhancement and suppression by manipulating attentional field size in a central load task and measuring visual evoked potentials (VEPs) across the visual field. Subjects performed an attentional load task in which they responded to visual targets that varied in color and orientation, updating every 1400 – 1550 ms. Assignment of visual targets alternated between blocks. In low-load blocks, visual targets were distinct in color from non-targets. In high-load blocks targets were discriminable from non-targets only by a identifying a conjunction between color and orientation. Attentional field size was also manipulated between blocks by scaling the size of stimuli in the load task between 1.0 and 2.5 degrees. While subjects performed the attentional load task, concentric checkerboard annuli were used to evoke cortical visual responses for five eccentricities across the visual field (0.5, 1.25, 4.0, 6.0, and 13.0 degrees). A randomly selected checkerboard annulus was contrast reversed every 300 – 650 ms. Separate VEPs were calculated for each level of attentional field size, attentional load, and annulus eccentricity. The early sensory components of these VEPs (P1 and N1) were assessed across the visual field for effects of attentional load and attentional field size. Manipulation of attentional field size resulted in robust differences in the distribution of attentional effects across the visual field (as indexed by P1 and N1) such that a smaller attentional field led to discrete attentional modulations of visual responses (enhancement and suppression) across the tested eccentricities whereas a larger attentional field induced broader and less well-defined attentional effects across space.
Meeting abstract presented at VSS 2014