Disparity-Tuning Characteristics of Neuronal Responses to Dynamic Random-Dot Stereograms in Macaque Visual Area V4

Abstract

Stereo processing begins in the striate cortex and involves several extrastriate visual areas. We quantitatively analyzed the disparity-tuning characteristics of neurons in area V4 of awake, fixating monkeys. Approximately half of the analyzed V4 cells were tuned for horizontal binocular disparities embedded in dynamic random-dot stereograms (RDSs). Their response preferences were strongly biased for crossed disparities. To characterize the disparity-tuning profile, we fitted a Gabor function to the disparity-tuning data. The distribution of V4 cells showed a single dense cluster in a joint parameter space of the center and the phase parameters of the fitted Gabor function; most V4 neurons were maximally sensitive to fine stereoscopic depth increments near zero disparity. Comparing single-cell responses with background multiunit responses at the same sites showed that disparity-sensitive cells were clustered within V4 and that nearby cells possessed similar preferred disparities. Consistent with a recent report by Hegdé and Van Essen, the disparity tuning for an RDS drastically differed from that for a solid-figure stereogram (SFS). Disparity-tuning curves were generally broader for SFSs than for RDSs, and there was no correlation between the fitted Gabor functions' amplitudes, widths, or peaks for the two types of stereograms. The differences were partially attributable to shifts in the monocular images of an SFS. Our results suggest that the representation of stereoscopic depth in V4 is suited for detecting fine structural features protruding from a background. The representation is not generic and differs when the stimulus is broad-band noise or a solid figure.

Neural Correlates of Fine Depth Discrimination in Monkey Inferior Temporal Cortex

“…Recent studies have shown the existence of disparity-selective neurons in the ventral visual pathway (Janssen et al, 1999;Uka et al, 2000;Connor, 2001, 2005;Watanabe et al, 2002;Tanabe et al, 2005). We have now shown the functional relevance of disparity-selective IT neurons in a depth discrimination task.…”

“…The distinction between the ventral and dorsal visual pathways (Ungerleider and Mishkin, 1982) cannot be based on the existence of disparity-selective neurons, because both pathways contain neurons sensitive for binocular disparity (Maunsell and Van Essen, 1983;Roy et al, 1992;Eifuku and Wurtz, 1999;Janssen et al, 1999;Taira et al, 2000;Uka et al, 2000;Connor, 2001, 2005;Watanabe et al, 2002;DeAngelis and Uka, 2003;Tanabe et al, 2005). The mere existence of these neurons does not reveal the functional role that these pathways play (Parker and Newsome, 1998).…”

“…In binocular vision, neurons selective for binocular disparities are found in many areas including the primary visual cortex (V1) and areas within the occipitoparietal (dorsal) visual pathway and the occipitotemporal (ventral) visual pathway (Hubel and Wiesel, 1970;Poggio and Fischer, 1977;Maunsell and Van Essen, 1983;Burkhalter and Van Essen, 1986;Felleman and Van Essen, 1987;Poggio et al, 1988;Roy et al, 1992;Eifuku and Wurtz, 1999;Janssen et al, 1999;Taira et al, 2000;Uka et al, 2000;Connor, 2001, 2005;Prince et al, 2002;Watanabe et al, 2002;DeAngelis and Uka, 2003;Tanabe et al, 2005). The specific roles that these multiple areas play in stereopsis are poorly understood.…”

“…In this study, we determined whether there is a correlation between the responses of disparity-selective neurons in the ventral visual pathway (Janssen et al, 1999;Uka et al, 2000;Connor, 2001, 2005;Watanabe et al, 2002;Tanabe et al, 2005) and the discrimination of fine-grain depth by monkeys. A recent study showed that disparity-selective neurons in the inferior temporal cortex (IT) are sensitive to small changes in disparity, especially near the plane of fixation (Janssen et al, 2000).…”

Neural Activity in Cortical Area V4 Underlies Fine Disparity Discrimination

“…Instead of exhaustively testing every possible variable of the task, we artificially boosted the activity of V4 neurons with electrical microstimulation in a separate set of sessions. We were able to selectively activate near-preferring or far-preferring neurons because V4 neurons are clustered according to its preferred disparity (see Materials and Methods, above) (Watanabe et al, 2002;Tanabe et al, 2005). If the monkeys based their decision on the representation of disparity in V4, we expected frequent decisions toward the preference of the stimulated site.…”