Okazaki Y, Fujita I.
Responses of disparity-sensitive V3/V3A neurons to anti-correlated random-dot stereograms.
Correlated random-dot stereograms (cRDSs) are often used to study depth perception. Depth perception is lost or reversed when using anti-correlated random-dot stereograms (aRDSs), in which the luminance contrast of dots is reversed between the two-eye images (Cumming et al, 1998; Tanabe et al, 2008). Single-unit recordings in monkey visual cortex have revealed that while most neurons in V1 retain disparity modulation for aRDSs, their disparity tuning curves are inverted compared to those for cRDSs (Cumming & Parker, 1997). Additionally, it has been observed that higher level inferior temporal cortex neurons are not disparity-selective for aRDSs (Janssen et al, 2003) and that V4 neurons greatly attenuate this selectivity (Tanabe et al, 2004). Unlike these regions, however, little is known about the responses of neurons in V3/V3A, an intermediate stage between V1 and V4, to aRDSs. Here we examined these responses by recording extracellular activity from 87 visually responsive neurons in two awake, fixating monkeys. Of these, seventy one showed significant selectivity for binocular disparity embedded in cRDSs (Kruskal-Wallis; p<0.05). The percentage of V3/V3A neurons selective for aRDSs (32%; 23/71) approximately equaled that in V4 (37%) (Tanabe et al, 2004). We fitted Gabor functions to the disparity tuning curves in order to calculate the ratio of disparity modulation amplitudes between aRDSs and cRDSs. The ratio for V3/V3A neurons (median, 0.25) was lower than that of V1 neurons (median, 0.39; Cumming & Parker, 1997) (Mann-Whitney test; p=0.0005), but comparable to that of V4 neurons (median, 0.24; Tanabe et al, 2004) (p=0.74). The results suggest that V3/V3A is involved in computations that eliminate any false-match responses elicited in V1.