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Nathan Parks, Diane Beck, Arthur Kramer; The Distribution of Attention in the Visual Field Under Perceptual Load. Journal of Vision 2011;11(11):234. doi: https://doi.org/10.1167/11.11.234.
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The perceptual load theory of attention proposes that the degree to which visual distractors are processed is a function of the perceptual demands of a task - greater perceptual demands result in increased distractor filtering. Here, we used steady-state visual evoked potentials (SSVEPs) to investigate the distribution of load-induced attentional filtering across the visual field. Electroencephalogram (EEG) was recorded while subjects performed a foveal go-nogo task under two levels of perceptual load. Task stimuli were rectangles that varied in color (black or white) and orientation (vertical or horizontal) and subjects were assigned two such rectangles as targets. Perceptual load was manipulated between blocks by assigning targets that could be discriminated on the basis of color alone (low load) or a conjunction of color and orientation (high load). The effect of load on the distribution of attention was assessed by presenting a contrast reversing ring at one of three eccentricities (2°, 6°, or 11°) during performance of the go-nogo task. Rings contrast reversed at 8.3 Hz, providing an EEG frequency-domain signature that could be used to track changes in visual processing as a result of perceptual load. Results showed that power at the 8.3 Hz frequency was reduced under high perceptual load (relative to low load) but only at the 2° eccentricity. These results suggest that perceptual load does not modulate visual processing equally across the entire visual field but primarily filters visual stimuli most proximal to task-relevant stimuli.
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