Abstract
Curvature is one of many visual features shown to be important for visual processing. For instance, curved features provide sufficient information for categorizing animate vs. inanimate objects without top-down processing in both human (Zachariou et al., 2018) and nonhuman primates (Yue et al., 2018). Theresults from our fMRI study in rhesus monkeys (Yue et al. 2014) have shed light on some of the neural mechanisms underlying curvature processing. We described a network of visual cortical areas selective for curvature, one of which, the posterior curvature-selective patch (PCP), is located in dorsal V4. The fMRI responses in the PCP correlated significantly with curved Gabor filter values calculated from experimental images. The current study investigated whether the PCP contains a columnar organization for curvature, similar to the columnar organization for orientation in V1 and that for direction-of-motion in MT. We conducted electrophysiological recordings in awake, behaving macaques (n = 2) as they viewed curved Gabors manipulated along three feature dimensions: degree of curvature, orientation, and size. With electrode penetrations tangential to the surface of PCP, we found that both orientation and an interaction between orientation and the degree of curvature of the stimuli significantly predicted the penetration distance of electrodes parallel to the surface of PCP in one of two macaques. This finding suggests that there may be curvature columns perpendicular to the surface, with orientation varying across columns within the same layer. Additional data with electrode penetrations perpendicular to the surface of PCP along with further analysis of data collected from the second monkey will provide clearer and more direct evidence for whether a columnar structure for the degree of curvature and orientation exists within PCP. The outcome of this study will advance our understanding of how middle-level visual features, such as curvature, are represented within macaque visual cortex.
Acknowledgement: NIMH intramural research program