Society for Neuroscience 2003
Prog#179.18

TUNING OF AREA V4 NEURONS TO HORIZONTAL BINOCULAR DISPARITY EMBEDDED IN CORRELATED AND ANTICORRELATED RANDOM-DOT STEREOGRAMS.
S.Tanabe1*; K.Umeda1; I.Fujita1,2
1. Lab. Cognit Neurosci., Dept. Biophys Eng, Grad. Sch. Eng Sci., Osaka Univ, Toyonaka, Japan
2. Grad Sch Frontier Biosci, Toyonaka, Japan

Depth is perceived from horizontal binocular disparity in a random-dot stereogram (RDS). By reversing the contrast of dots seen by one of the eyes to generate an anti-correlated RDS, the perception of depth is lost or diminished. Several investigations exploited this perceptual phenomenon for testing whether neural responses correlate with stereoscopic depth perception. In the striate cortex and extrastriate cortical areas MT and MST, the majority of neurons are selective for horizontal disparity in RDSs, and only a small number of neurons in these areas lose their disparity selectivity when anticorrelated. Neuronal activities in these areas thus do not correlate with the stereoscopic perception of depth. We examined neural responses to correlated and anticorrelated RDSs in area V4 in three awake, fixating monkeys (Macaca fuscata). More than half of the cells (70/132) significantly modulated their responses according to disparities in a patch of correlated RDSs (Kruskal-Wallis test p<0.05). Preferred disparity were similar between single unit and multi unit activities, thus disparity preference was shared among adjacent cells (r = 0.48, p<0.0001). Most disparity selective cells (45/70) lost their selectivity for disparity when the RDS was anti-correlated. For a quantitative analysis of disparity tuning, data were fit with Gabor functions. The mean ratio of the modulation amplitude between correlated and anticorrelated RDSs was 0.25 in V4. The reduction in the amplitude modulation from correlated to anticorrelated RDSs was more prominent in V4 than in V1 where the mean amplitude ratio is 0.52 (Cumming and Parker 1997). Our results suggest that local matches detected in V1 are rejected via neuronal processing along the ventral visual pathway, leading to a cortical representation of global stereoscopic matches at higher areas.