Enhancement and suppression in the visual field under perceptual load

The perceptual load theory of attention proposes that the degree to which visual distractors are processed is a function of the attentional demands of a task-greater demands increase filtering of irrelevant distractors. The spatial configuration of such filtering is unknown. Here, we used steady-state visual evoked potentials (SSVEPs) in conjunction with time-domain event-related potentials (ERPs) to investigate the distribution of load-induced distractor suppression and task-relevant enhancement in the visual field. Electroencephalogram (EEG) was recorded while subjects performed a foveal go/no-go task that varied in perceptual load. Load dependent distractor suppression was assessed by presenting a contrast reversing ring at one of three eccentricities (2, 6, or 11 degrees) during performance of the go/no-go task. Rings contrast reversed at 8.3 Hz, allowing load-dependent changes in distractor processing to be tracked in the frequency domain. ERPs were calculated to the onset of stimuli in the load task to examine load-dependent modulation of task-relevant processing. Results showed that the amplitude of the distractor SSVEP (8.3 Hz) was attenuated under high perceptual load (relative to low load) at the most proximal (2 degrees) eccentricity but not at more eccentric locations (6 or 11 degrees). Task-relevant ERPs revealed a significant increase in N1 amplitude under high load. These results are consistent with a center surround configuration of load-induced enhancement and suppression in the visual field.