Three-dimensional visual information processing in the parietal cortex

点击翻译按钮获取中文摘要

In order to elucidate the neural mechanisms involved in the perception of the three-dimensional (3D) orientation of a surface, we trained monkeys to discriminate the 3D orientation of a surface from binocular disparity cues using a Go/No-go type delayed-matching-to-sample (DMTS) task and examined the properties of the surface-orientation-selective (SOS) neurons. We recorded SOS neurons from the caudal part of the lateral bank of the intraparietal sulcus (area CIP) of Japanese monkeys (Macaca fuscata). We tested SOS neurons using the square plate of a solid figure stereogram (SFS) and random-dot stereogram (RDS) without perspective cues ; almost all of tested neurons showed surface orientation selectivity for the SFS and/or the RDS without perspective cues. These results suggest that neurons which show surface orientation tuning for the RDS without perspective cues compute surface orientation from the gradient of the binocular disparity and neurons which show surface orientation tuning … More for the SFS without perspective cues may represent surface orientation primarily from the gradient of the binocular disparity along the contours. Furthermore, we investigated the effects of linear perspective cues on the response of SOS neurons. Neurons were tested using the solid figure with perspective cues alone. More than half of tested neurons were sensitive to both perspective and disparity cues, but a few were sensitive to perspective cues alone. The response magnitude to the solid figure with perspective cues alone was weaker than that with disparity cues, suggesting the integration of both cues for the perception of surface orientation, however, the dominance of disparity cues. We also tested the effects of texture gradient. Many neurons were sensitive to the texture gradient, and more than half of them were also sensitive to the disparity gradient, suggesting that texture gradient information is integrated with disparity gradient in area CIP.These results suggest that the monocular depth cues are integrated with the disparity cues in area CIP to build up a generalized representation of surface orientation independent of the source of information. Finally, cortical activities were examined using functional magnetic resonance imaging (fMRI) while subjects discriminated whether the central part of the surface was protruded or recessed based on shading without any binocular disparity cues and the right intraparietal area was shown to be activated. This result strongly suggests that the intraparietal area plays an important role in perception of a 3D structure of a surface, even when based only on monocular depth cues without binocular disparity cues.In conclusion, the SOS neurons in the area CIP are likely to operate higher order processing of disparity signals for surface perception by integrating the several kinds of depth cues. Less