A specialization for relative disparity in V2

136

144

In the macaque extrastriate cortex, robust correlations between perceptual choice and neuronal response have been demonstrated, frequently quantified as choice probabilities (CPs). Such correlations are modest in early visual cortex, suggesting that CPs may depend on the position of a neuron in the hierarchy of visual processing. However, previous studies have not compared neurons with similar precision in equivalent tasks.We investigated the role of cortical hierarchy on CP using a task for which significant CPs have been described previously for middle temporal area (MT). We measured CPs in disparity-selective neurons from both V1 and V2. The stimulus was a dynamic random dot stereogram, presented with a near or a far disparity, masked by varying numbers of binocularly uncorrelated dots. Two macaque monkeys reported whether they perceived a circular patch in front or behind a surrounding annulus in a forced choice task.For V2 (n ϭ 69), CP was on average 0.56, the first demonstration of systematic CPs in a visual area as early as V2. In V1 (n ϭ 74), average CP was at chance level (0.51). The pattern was similar in a subgroup of neurons selected such that the statistical precision in the task was on average identical to that reported for MT (mean CP, 0.51 for V1, n ϭ 33; 0.58 for V2, n ϭ 54). This difference between V1 and V2 could not be explained by eye movements, stimulus size relative to the receptive field, or differences in disparity tuning. Rather, it seems to reflect a functional difference (at least in disparity processing) between striate and extrastriate cortex.

Section: Effect Of Other Tuning Properties On Choice Probabilities In V2supporting

confidence: 57%

“…A previous study showed that a proportion of V2 neurons were specialized for signaling relative disparity (Thomas et al, 2002). We characterized relative disparity only in a small number of the V2 neurons (n ϭ 17).…”

Section: Effect Of Other Tuning Properties On Choice Probabilities In V2mentioning

confidence: 99%

Macaque V2 Neurons, But Not V1 Neurons, Show Choice-Related Activity

Nienborg¹,

Cumming²

2006

136

144

“…Similarly, Hegde and Van Essen (2000) invoked the idea of convergence from V1 onto V2 cells to account for selectivity for complex contours. Similar schemes may also explain responses to motion borders (Marcar et al, 2000), illusory contours (von der Heydt et al, 1984(von der Heydt et al, , 1992, and relative disparity (Thomas et al, 2002).…”

Section: Discussionmentioning

confidence: 94%

A Simple Account of Cyclopean Edge Responses in Macaque V2

Bredfeldt

Cumming

2006

It has been shown recently that neurons in V2 respond selectively to the edges of figures defined only by disparity (cyclopean edges). These responses are orientation selective, often preferring similar orientations for cyclopean and luminance contours, suggesting that they may support a cue-invariant representation of contours. Here, we investigate the extent to which processing of purely local visual information (in the vicinity of the receptive field) might explain such results, using the most impoverished stimulus possible containing a cyclopean edge (a circular patch of random dots divided into two regions by a single edge). Many V2 cells responded better to the cyclopean edge than to uniform disparities, and most of these were at least broadly selective for the orientation of the cyclopean edge. Two characteristics argue against a cue-invariant contour representation: (1) the cyclopean edge response was frequently abolished by small changes to the component disparities; and (2) although V2 cells frequently responded to both signs of a cyclopean edge (defined by which side of the edge is in front), they did so at different edge locations. These characteristics are consistent with a simple feedforward scheme in which V2 neurons receive inputs from several V1 subunits with different disparity selectivity. We also found a correlation between the preferred orientations for cyclopean edges and contrast stimuli, suggesting that this feedforward wiring is not random. These characteristics suggest that V2 responses to cyclopean edges may be useful in supporting a cue-invariant contour representation higher in the visual pathway.

“…This study investigated the organization of the binocular RFs of neurons in the early visual cortex, which are the lowest-level building blocks of depth-information processing in the brain (Maunsell and Van Essen, 1983;Ohzawa et al, 1990;Janssen et al, 1999;Taira et al, 2000;Connor, 2001, 2002;Prince et al, 2002a,b;Thomas et al, 2002;Nguyenkim and DeAngelis, 2003;Tanaka and Ohzawa, 2006). By analyzing the responses to dynamic 2D dichoptic random-dot stimuli whose patterns were uncorrelated between the two eyes, binocular interactions were examined for a pair of both X and Y positions in the RFs of single neurons.…”

Section: Discussionmentioning

confidence: 99%

Complex Cells in the Cat Striate Cortex Have Multiple Disparity Detectors in the Three-Dimensional Binocular Receptive Fields

Sasaki¹,

Tabuchi²,

Ohzawa³

2010

Along the visual pathway, neurons generally become more specialized for signaling a limited subset of stimulus attributes and become more invariant to changes in the stimulus position within the receptive fields (RFs). One of the likely mechanisms underlying such invariance appears to be pooling of detectors located at different positions. Does such spatial pooling occur for disparity-selective neurons in primary visual cortex? To examine whether the three-dimensional (3D) binocular RFs are constructed by pooling detectors for binocular disparity, we investigated binocular interactions in the 3D space for neurons in the cat striate cortex. Approximately one-third of complex cells showed the spatial pooling of disparity detectors to a significant degree, whereas the majority of simple cells did not. The degree of spatial pooling of disparity detectors along the preferred orientation axis was generally larger than that along the axis orthogonal to the orientation axis. We then reconstructed 3D binocular RFs in their complete form and examined their structures. Disparity tuning curves were compared across positions along the orientation axis in the RFs. A small population of cells appeared to show a gradual shift of the preferred disparity along this axis, indicating that they can potentially signal inclination in the 3D space. However, the majority of cells exhibited a position-invariant disparity tuning. Finally, disparity tuning curves were examined for all oblique angles in addition to horizontal and vertical. Tunings were broadest along the orientation axis as the disparity energy model predicts.