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Roberto Cipriani, Christopher Pack; Direction selectivity of center-surround interactions in macaque MT. Journal of Vision 2010;10(7):933. doi: 10.1167/10.7.933.
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© ARVO (1962-2015); The Authors (2016-present)
One of the primary functions of neurons in the extrastriate cortex is to integrate motion signals from lower visual areas. In addition to this integrative function, many extrastriate neurons appear to respond best to motion stimuli that differ across space. These neurons are suppressed by visual motion stimuli placed outside of their classical receptive fields. To gain a better understanding of these center-surround interactions, we recorded from neurons in visual area MT of the alert macaque during presentation of stimuli that moved in different directions in the receptive field centers and surrounds. In the first set of experiments, neurons were tested using one direction for the center while the surround direction was varied. We quantified the strength of suppression as the reduction in response evoked by each direction of the surround relative to the response evoked by only the center stimulus moving in the preferred direction of motion. Surprisingly, a large proportion of cells showed the strongest suppression when the surround motion was orthogonal to the center direction of motion Most of these cells were classified as lacking surround suppression when tested only with surround stimuli moving in the direction preferred by the receptive field center. This suggests that the vast majority of MT cells are surround-suppressed provided that the appropriate stimulus is used to drive the surround. In another set of experiments, we varied the contrast of the center and the surround stimuli independently. When looking at conditions with a low contrast center and high contrast surround, the tuning of the center stimulus for the cell shifted with the changes in motion direction of the surround stimulus. This suggests that the surround direction affects the tuning of the center stimulus. Supported by CIHR and MDEIE.
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