Different perceptual decoding architectures for the central and peripheral vision revealed by dichoptic motion stimuli L Zhaoping |
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University College London, United Kingdom
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| V1 encodes both the summation of visual inputs to the two eyes and the difference between these inputs (Li and Atick, 1994, Network,5(2),157-174). However, perception favours the sum. If flashing gratings cos(kx+p)cos(ft+q) and sin(kx+p)sin(ft+q) are shown to the left and right eyes respectively, (x: space; t: time; k: spatial frequency; f: temporal frequency), binocular summation and difference each contains a drifting grating, but with opposite drift directions. The summation rather than the difference direction is more likely perceived with a brief (e.g., 0.5 second) foveal viewing of this dichoptic stimulus (Shadlen and Carney, 1986, Science,232(4746),95-97). I found this bias for binocular summation to be absent with peripheral viewing (about 10 degree eccentricity; stimulus enlarged to counter acuity change). Furthermore, reducing the drifting speed (by decreasing f from 5 Hz to 2.5 Hz), likely facilitating top-down visual feature tracking, increased this bias in central, but not peripheral, vision. Since higher visual areas critical for recognition are devoted to central vision, I suggest that the summation bias arises because top-down feedback generative signals, which enjoy binocular correlations based on visual input statistics, are involved in foveal analysis (recognition) by synthesis, but that these signals are weaker or unavailable in the periphery. |
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