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Simo Vanni, Michel Dojat, Jan Warnking, Christoph Segebarth, Jean Bullier; Global interaction appears first in the temporo-occipital cortex. Journal of Vision 2003;3(9):153. doi: 10.1167/3.9.153.
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© ARVO (1962-2015); The Authors (2016-present)
Psychophysical evidence suggests that information is integrated across the visual field early, and physiological data and models suggest that global information might have an important role in directing early cortical processing. In order to test for such early effects of global interactions on local processing, we tried to determine where and when the responses to two different visual stimuli are combined together in the human cortex. We showed two checkerboard patterns either simultaneously or one at the time, first in the left lower visual quadrant, and then at symmetrical positions in the left and right lower quadrants. Visual evoked potential (VEP) and functional magnetic resonance imaging (fMRI) data was acquired separately, but with identical stimulus parameters, and the retinotopic areas were mapped separately with fMRI. We acquired the position and orientation of the VEP sources in the retinotopic areas directly from fMRI, whereas other sources were modelled from the VEP data. Area V1 activated first, starting at 50 ms, and a temporo-occipital site located in the LOC/ V5 region followed soon, only about 10–15 ms after V1. Interaction was estimated by comparing the VEP source amplitude for the two simultaneous patterns to the sum of the single pattern responses. For the left visual field stimuli, the earliest interaction appeared at 80 ms in the right temporo-occipital region. When patterns were presented in two different hemifields, interaction appeared again first in the temporo-occipital region, bilaterally, and started at about 100–110 ms latency. The retinotopic areas (V1, V2, V3, and V3a), as well as other sources, showed linear summation of responses for the two patterns at these latencies, and interactions appeared later. According to our data the earliest global interactions emerge in a temporo-occipital region located near V5 and LOC, starting 30 ms after the first afferent volley reaches the cortex.
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