Representation of Stereoscopic Depth in Pooled Responses of Macaque V4 Neurons M Abdolrahmani1, T Doi2, H M Shiozaki3, I Fujita1 |
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1Frontier Biosciences School, Lab for Cognitive Neurosciences, Osaka University, Japan |
| Stereoscopic depth perception is as vivid for half-matched random dot stereograms (i.e. RDSs with zero binocular correlation) as for correlated RDSs [Doi et al, 2011, J. Vision, 11(3):1, 1–16]. We studied the underlying neural mechanisms by recording single-neuron responses of macaque visual area V4, which attenuates disparity selectivity for anti-correlated RDSs [Tanabe et al, 2004, J. Neuroscience, 24(37), 8170–8180]. Binocular disparity and the level of anti-correlation (% of contrast reversed dots) were varied across trials while monkeys performed a fixation task. Half the tested (51/103) cells were significantly disparity selective for cRDSs. Slight anti-correlation (35%) markedly decreased the amplitude of disparity tuning curves. The phase (shape) of the tuning curves, however, did not change when anti-correlation was applied up to half the dots (<50%). In contrast, the phase shifted unpredictably across V4 neurons as anti-correlation became stronger (>50%). Therefore, pooling responses across cells may account for depth perception. For instance, the pooled responses can signal disparity for half-matched RDSs (50%), because the shape of attenuated individual tuning is consistent within a pool. We suggest that neurons in downstream areas that pool V4 disparity-selective responses might be a direct correlate of binocular depth for any level of correlation between left and right images. |
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