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Bruce G Cumming, Jenny C Read; Sensitivity to interocular delay in binocular V1 neurons. Journal of Vision 2003;3(9):61. doi: 10.1167/3.9.61.
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© ARVO (1962-2015); The Authors (2016-present)
In natural viewing, image changes almost invariably occur simultaneously in the two eyes. Even when the Pulfrich effect is induced with a neutral density filter, the inter-ocular delay (∼10ms) is small relative to the integration time of many cortical neurons. We investigated whether the brain exploits this binocular simultaneity when computing disparities by recording the responses of disparity selective V1 neurons to dynamic random dot stereograms (72Hz) in two awake fixating monkeys. Interocular delay was manipulated (in steps of one frame, 14ms) by delaying or advancing the sequence of of dot patterns shown to one eye. Disparity selectivity was measured at a range of interocular delays. Most neurons were exquisitely sensitive to interocular delay. For 22/38 neurons (58%), a delay of only one video frame reduced the magnitude of the disparity selective response by at least 40%. This suggests that binocular integration occurs over a short time scale. The psychophysical consequences of an interocular delay were even more dramatic. In one of the monkeys and in two human observers, a delay of 14ms caused at least a fivefold increase in disparity threshold. These physiological and psychophysical data indicate that some aspects of binocular combination occur with high temporal resolution. A number of previous psychophysical studies have indicated that stereopsis is a sluggish process with long integration times. These observations can be reconciled if one supposes that there are two separate stages in the temporal processing of disparity. The first stage has high temporal resolution and is therefore able to exploit binocular simultaneity. The second stage integrates the output of the first stage over longer time periods. The sensitivity of V1 neurons to interocular delay suggests that this first stage occurs in V1.
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