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Kiley Seymour, Susan Wardle; Differential orientation tuning of near and far surround suppression in human V1. Journal of Vision 2017;17(10):797. doi: 10.1167/17.10.797.
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© ARVO (1962-2015); The Authors (2016-present)
Responses to stimuli placed within a neuron's receptive field are modulated by stimuli in surrounding regions. Contextual modulation of neural responses in primary visual cortex (V1) is orientation-tuned. Human fMRI experiments show greater suppression of the BOLD response to a target stimulus when the target and surrounding stimuli are the same orientation, and weakest suppression when the target and surrounding stimuli are orthogonal. Monkey physiology and human psychophysics suggest that two distinct mechanisms underlie orientation-specific contextual suppression in V1. The first inhibits sensory responses from a short range and is strongly tuned for orientation (geniculo-cortical and horizontal V1 connections). The second involves long-range inhibition that is less orientation-tuned (feedback from extrastriate cortex). Here we aimed to examine the orientation-tuning of these two mechanisms in human V1 with fMRI by manipulating the spatial extent of the surround to selectively probe either short or long-range mechanisms. We measured fMRI BOLD responses to a target grating annulus (1.5-3.5 deg eccentricity) in the presence of six different surround stimuli in ten naive observers. Surrounds were either oriented parallel or orthogonal to the target grating and were one of three sizes (Full: 3.5-9.5 deg eccentricity, Near: 3.5-6 deg eccentricity, Far: 6-9.5 deg eccentricity). Observers completed an orientation-matching task at central fixation. For the full surround, we replicated the finding of greater suppression of the BOLD response to the target for parallel surrounds compared to orthogonal surrounds. Similar orientation tuning of contextual suppression was observed for the near surround. However, for the far surround there was no difference in suppression of the BOLD response for orthogonal versus parallel gratings, suggesting far surround suppression is un-tuned for orientation. Our findings from human V1 are consistent with the spatial extent of orientation tuning of surround suppression observed in macaque primary visual cortex and human psychophysics.
Meeting abstract presented at VSS 2017
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