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Laura Palmieri, Sid Henriksen, Jenny Read, Bruce Cumming; The effect of interocular contrast on disparity tuning in primary visual cortex. Journal of Vision 2018;18(10):133. doi: https://doi.org/10.1167/18.10.133.
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© ARVO (1962-2015); The Authors (2016-present)
Reducing contrast has little effect on psychophysical stereoacuity, except at very low contrast. Differences in contrast between the eyes are more disruptive. The effect of contrast on disparity selectivity in cortical neurons has been investigated only in the cat with grating stimuli. Here we report the effects of stimulus contrast on disparity selectivity in 38 disparity-tuned neurons recorded from V1 of the awake fixating primate. The stimulus was a dynamic 1-dimensional noise pattern ("barcode"), to which disparity was applied. The stimulus (duration 750ms) was presented at either 20% (L) or 100% (H) contrast in each eye, and all four combinations (HH,LL,LH,HL) were used. We used the high contrast condition (HH) as a reference, and plotted responses to correlated disparity in the other three conditions relative to this. The slope of a type II regression was then used to quantify relative response strength in the other three conditions. Reducing contrast in either or both eyes reduced the strength of disparity selectivity (median ratio 0.83 for LL vs HH, 0.59 for LH and HL vs HH, both significantly different from 1, p=0.03 and < 0.001, sign test). Reducing contrast in one eye only does have a slightly greater effect on disparity tuning compared compared to reducing it in both (median ratio 1.27 for LL vs LH and HL; significantly different from 1, p=0.02), which is qualitatively in agreement with psychophysics. However, the 40% reduction in signal strength for LH and HL relative to HH is larger than the psychophysical effects reported for interocular contrasts in the same range. One explanation for this difference could be that those neurons most affected by interocular contrast differences are given less weight in stereoacuity tasks.
Meeting abstract presented at VSS 2018
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