Neurons in monkey visual area V2 encode combinations of orientations.

Contours and textures are important attributes of object surfaces, and are often described by combinations of local orientations in visual images. To elucidate the neural mechanisms underlying contour and texture processing, we examined receptive field (RF) structures of neurons in visual area V2 of the macaque monkey for encoding combinations of orientations. By measuring orientation tuning at several locations within the classical RF, we found that a majority (70%) of V2 neurons have similar orientation tuning throughout the RF. However, many others have RFs containing subregions tuned to different orientations, most commonly about 90 degrees apart. By measuring interactions between two positions within the RF, we found that approximately one-third of neurons show inhibitory interactions that make them selective for combinations of orientations. These results indicate that V2 neurons could play an important role in analyzing contours and textures and could provide useful cues for surface segmentation.