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Hee-kyoung Ko, Nan R. Zhang, Rüdiger von der Heydt; Context integration across hemispheres in neurons of the visual cortex. Journal of Vision 2011;11(11):1074. doi: 10.1167/11.11.1074.
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© ARVO (1962-2015); The Authors (2016-present)
Most neurons in visual cortex respond to contrast borders and are orientation selective, and some are also selective for which side of a border is figure and which side is ground (‘border ownership coding’). These neurons are influenced by the image context far beyond the classical receptive field (CRF), and as early as 25 ms after the onset of activity in the cortex. Using fragmented figures, Zhang and von der Heydt (J Neuroscience 2010) were able to quantify the contribution of each part of the figure contour. They found that contours on the preferred border ownership side facilitated, while contours on the non-preferred side suppressed responses, with about 80% of the locations contributing on average. Here, we studied context integration across the cerebral hemispheres. Neurons were recorded from monkey V2 under behaviorally induced fixation. The basic test figure was a contour-defined square akin to the Cornsweet illusion that could be decomposed into eight fragments. One edge was centered in the CRF, and the fragments outside the CRF were presented in varied composition. Some of the fragments were in the same hemifield as the CRF, and thus represented in the same hemisphere with the recorded neuron, whereas others were in the opposite hemifield and could influence the neuron only through interhemispheric commissures. Using linear regression, we computed the influences of individual fragments as a function of time after stimulus onset. We found no significant difference in time course between the context influences from the two hemifields, whether facilitatory or suppressive. Thus, border ownership selective neurons integrate information evenly across hemispheres. The interhemispheric transfer does not seem to cause major delays.
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