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Kristy A. Sundberg, Jude F. Mitchell, John H. Reynolds; Contrast dependant center-surround interactions in macaque area V4. Journal of Vision 2005;5(8):79. doi: 10.1167/5.8.79.
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© ARVO (1962-2015); The Authors (2016-present)
Visual neurons integrate information over large regions of space beyond their classical receptive fields. A stimulus presented alone in this surround region does not elicit a response, but can modulate the response evoked by a simultaneously presented center stimulus. Center-surround interactions have been studied in V1 and MT but less is known about their properties in V4. We characterized the contrast dependence of center-surround interactions in V4 of the awake monkey. On each trial two luminance-modulated gratings were presented, one within the classical receptive field and the other in the surround. The monkey fixated and performed an attention demanding multi-object tracking task in the opposite hemifield. We measured the contrast response function to the center stimulus and observed how it changed with the addition of different contrast surround stimuli. Surround stimuli generally exerted a suppressive influence on the response evoked by the center stimulus. Consistent with findings in the anesthetized monkey V1, this suppressive effect could best be characterized as a rightward shift in the contrast response function for some cells, while for other cells suppression reduced the upper asymptote of the contrast response function. Suppressive effects generally increased with the luminance contrast of the surround stimulus. Although less common, surround stimulus facilitation was also observed, with some cells showing facilitation at low center contrasts and others showing facilitation at higher center contrasts. These findings show that strong center-surround modulations are induced in V4 by a single grating in the surround, but that the nature of the modulation varies from cell to cell.
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