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Haidong D. Lu, Michael Kraus, Anna W. Roe; Optical imaging of contrast response in functional domains in V1 and V2 of macaque visual cortex. Journal of Vision 2004;4(8):275. doi: 10.1167/4.8.275.
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© ARVO (1962-2015); The Authors (2016-present)
Our recent optical imaging and single unit studies in visual cortex suggested a preferential involvement of V1 blobs and V2 thin stripes in real and illusory brightness response (Hung et al. Soc Neurosci 2002; cf. Hung et al Vision Res 2001). To further explore this possibility and to better relate full field brightness response to standard contrast sensitivity responses, we have measured contrast response of different functional domains in V1 and V2 with optical imaging and electrophysiological recording. Visual stimuli consisted of drifting horizontal and vertical luminance sine wave gratings with different spatial frequencies, ranging from 0.84 — 7.6 cyc/deg. Luminance contrast of the gratings was varied over four different levels (10%, 20%, 40%, 80%). Intrinsic signals were imaged from area V1 and V2 of anesthetized macaque monkeys. Average reflectance values from functional domains (orientation domains in V1 and V2, blobs in V1, and thin and thick/pale stripes in V2) were obtained and were also compared to single cell responses sampled from superficial layers of imaged domains. Results showed that, as expected, cortical reflectance values changed systematically with the contrast level of the stimulus: the greater the contrast, the greater the response. As measured by reflectance values, we find that, at low spatial frequencies and low contrast levels, V1 blobs have greater response than V1 interblobs. In comparison to V1 domains, V2 domains exhibit higher contrast gain and saturate at a low-mid contrast levels. V2 thin stripes also showed higher contrast gain than thick/pale stripes. These preliminary findings are consistent with the proposed role of V1 blobs and V2 thin stripes in processing of brightness information.
NEI, Packard Foundation
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