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Weifeng Xu, Zhiming Shen, Chaoyi Li; Figure-ground segregation and spatial phase tuning of extra-receptive field of V1 neurons in awake monkey. Journal of Vision 2003;3(9):245. doi: 10.1167/3.9.245.
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Segregating a figure from a background is one of the most fundamental tasks that have to be performed by the visual system. In the primary visual cortex (V1), the majority of cells respond preferentially to line segments with a specific orientation. This selectivity enables V1 neurons to isolate an object from its background on the basis of differences in segment orientation. Psychophysically “pop-out” figures can also be constructed with an iso-orientation configuration, in which the line segments confined to the figure differ in terminations or spatial phase from the line segments confined to the background. In the iso-orientation paradigm, the only cue that can be used to separate figure from background is the difference in relative spatial phase of the constituent lines between figure and background. In the present study, we measured the spatial phase tuning of the ERF (side- and end- regions) for neurons in the primary visual cortex of awake monkey (macaca mulata). We evaluated the tuning by varying the relative spatial phase between a grating confined to the excitatory RF and a grating confined to the inhibitory end- or side regions. Our results showed that the response of the V1 cells depends on the relative spatial phase of gratings between the CRF and ERF. To investigate which neural mechanisms underlie this capacity and why only some proportion of V1 cells respond to such subjective contours, we determined the relationship between spatial-phase sensitivity and strength of surround inhibition at the end- and side regions, a significant linear relationship was established. It is concluded that the V1 cells in primates can encode subjective contours, and that this ability is highly correlated with the spatial-phase-dependent center-surround interactions.
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