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Suzanne P. McKee, Alex R. Wade, Yury Petrov, Anthony M. Norcia; The neural correlates of human surround suppression. Journal of Vision 2006;6(6):202. doi: 10.1167/6.6.202.
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© ARVO (1962-2015); The Authors (2016-present)
The perceived contrast of a target is reduced by a higher contrast annular surround that shares the orientation and spatial frequency of the central target. In the fovea, perceived target contrast is somewhat suppressed by a surround, but, in the periphery, suppression of perceived contrast is much stronger. Like perceived contrast, contrast detection is also impaired by high contrast surrounds. However, there are important differences between the two measures. The surround only affects contrast thresholds for peripheral, not foveal, targets, and threshold suppression is more tightly tuned for orientation than is suppression of perceived contrast. To explore the neural origin of these suppression effects, we made high density EEG recordings. Observers passively viewed temporally modulated Gabor targets presented at 0 and 12 deg eccentricity, either alone or surrounded by higher contrast collinear or orthogonal gratings of the same spatial frequency; target and surround had different temporal frequencies. We used the minimum norm distributed inverse to measure current density signals in fMRI-defined visual areas V1, V2, V3, V3a, V4 and hMT+. Within V1, both foveal and peripheral target responses were suppressed by surrounds, with the periphery showing more suppression and stronger orientation tuning. The pattern of results was more similar to surround effects on perceived contrast than on contrast detection. Both perceived contrast and EEG potentials probably depend on massed output of a heterogeneous neural population, while thresholds may depend on a select subset of active neurons.
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