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Wilson Geisler, Duane Albrecht, Alison Crane; Responses of striate cortex neurons to transient changes in local contrast and luminance. Journal of Vision 2007;7(9):324. doi: 10.1167/7.9.324.
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© ARVO (1962-2015); The Authors (2016-present)
During normal saccadic inspection of natural images the receptive fields of cortical neurons are bombarded with frequent simultaneous changes in local mean luminance and contrast, yet there have been no systematic studies of how cortical neurons respond to such stimulation. The responses of single neurons in the primary visual cortex of the cat were measured for 200 ms presentations of sine wave gratings confined to the conventional receptive field. Both local mean luminance and contrast were parametrically and randomly varied over the 1–1.5 log unit ranges that are typical of natural images (Frazor & Geisler 2006, Vis Res., 46, 1585–1598). We find that responses are strongly modulated by both the local mean luminance and contrast, but in an approximately separable fashion—the contrast response function is approximately invariant except for a scale factor that depends upon the local mean luminance. The shapes of the temporal response profiles were found to be approximately invariant with contrast (in agreement with Albrecht et al. 2002, J. Neurophys., 88, 888–913), but were strongly affected by the local mean luminance. The results suggest that most, if not all, cortical neurons carry substantial local luminance information. The powerful non-linear effects of transient changes in local luminance on the contrast responses of cortical neurons may help explain why standard methods of characterizing receptive fields do a poor job of predicting responses to natural stimuli.
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