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Michael Silver, Anna Kosovicheva, Ayelet Landau; ERP correlates of orientation-specific surround suppression. Journal of Vision 2011;11(11):1168. doi: 10.1167/11.11.1168.
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Surround suppression–the reduction in perceived contrast of a center stimulus and the visual response to that stimulus in the presence of a high-contrast surround–is greatest when the center and surround stimuli share the same orientation. We examined the electrophysiological correlates of orientation-specific surround suppression using event-related potentials (ERPs). Displays contained a circular sinusoidal grating consisting of separate annulus (center) and surround regions. On each trial, the surround was presented in isolation for 500–1000 ms, followed by the annulus (with continuing presentation of the surround) for 400 ms. ERPs in response to the onset of the annulus were recorded for different annulus and surround orientations. In separate blocks, we varied the orientation of the surround grating such that it was either parallel or orthogonal to the annulus. Participants performed a contrast decrement detection task within the annulus, and the contrast of the target was adaptively varied using a psychophysical staircase procedure in order to equate task difficulty across all conditions. We measured contrast-decrement detection thresholds and P1 and N1 components of the ERP responses to the onset of the annulus for both parallel and orthogonal orientation conditions. Behaviorally, we found orientation-specific surround suppression: contrast decrement detection performance was worse when the surround had the same (parallel) orientation compared to when the annulus and surround were orthogonally oriented. In addition, amplitudes of the P1 and N1 components of the response to the annulus were smaller when the annulus was presented within a parallel, compared to an orthogonal, surround. Finally, behavioral indices of orientation-specific surround suppression for individual subjects were positively correlated with the magnitude of orientation-specific surround suppression of ERP amplitudes.
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