Integration of color, orientation, and size functional domains in the ventral pathway

Abstract

Functional specialization within the extrastriate areas of the ventral pathway associated with visual form analysis is poorly understood. Studies comparing the functional selectivities of neurons within the early visual areas have found that there are more similar than different between the areas. We simultaneously imaged visually evoked activation over regions of V2 and V4 and parametrically varied three visual attributes for which selectivity exists in both areas: color, orientation, and size. We found that color selective regions were observed in both areas and were of similar size and spatial distribution. However, two major areal distinctions were observed: V4 contained a greater number and diversity of color-specific regions than V2 and exhibited a higher degree of overlap between domains for different functional attributes. In V2, size and color regions were largely segregated from orientation domains, whereas in V4 both color and size regions overlapped considerably with orientation regions. Our results suggest that higher-order composite selectivities in the extrastriate cortex may arise organically from the interactions afforded by an overlap of functional domains for lower order selectivities.

Curvature domains in V4 of Macaque Monkey

“…As shown in Table S1, almost all experiments described in this study were conducted in at least two cases. Consistent with previous studies (15-17), alternating regions (bands) of color preference vs. orientation preference were observed, with small regions of overlap (Fig. S1).…”

“…Pinwheels are hypothesized to be landmarks of continuous ‘polymaps’ (for optimal representation of multiple feature spaces within a single area) and have been observed in both experimental data and computational models (21-23). Such structures have been previously observed in orientation maps and color maps in V1 (22, 24-26), V2 (27), and V4 (15, 17, 28) and more recently has been proposed as a fundamental unit of the orientation hypercolumn in V1 (26). To better evaluate this possibility, we conducted another experiment using a finer gradation of orientations (8 different orientations).…”

“…In addition, the sizes of curvature domains (mean = 434 μm for all 3 cases, see Fig. S8) fall within the 200-500 μm range of functional domain sizes within V4 (15-17). These data thus suggest that curvature maps are not artifactual and are distinct from previously described functional maps in V4.…”

“…However, it is unknown whether such neuronal responses are organized in any way akin to orientation maps in V1 and V2. Previous studies have shown the functional organization of V4 comprises alternating bands of ‘orientation’ and ‘color’ preference (15-17), as well as organization for disparity defined orientation (18), motion direction (16), and spatial frequency (19), but maps for curvature organization have not been demonstrated. Here, we hypothesized that orientation bands in V4 are regions of shape representation that include both orientation and curvature domains.…”

Brain rhythms shift and deploy attention

“…The physical difference between a yellow versus a blue fixation point is expected to cause local effects in neurons that are selective for the representation of the fovea and that are color selective. Neurons selective for different colors are partly intermingled within cortical areas (26, 27), such that our recordings with 1 mm diameter ECoG electrodes might well average over different color domains and thereby reduce or even eliminate color-differential responses. Potential residual color-differential responses in individual recording sites should be further reduced by our averaging over all recording sites in a given area.…”