Abstract
The primate visual system consists of a ventral stream, specialized for object recognition, and a dorsal visual stream, which is crucial for spatial vision and actions. However, little is known about the interactions and information flow between these two streams. We investigated these interactions within the network processing three-dimensional (3D) object information, comprising both the dorsal and ventral stream. Reversible inactivation of the macaque caudal intraparietal area (CIP) during functional magnetic resonance imaging (fMRI) reduced fMRI activations in posterior parietal cortex in the dorsal stream and, surprisingly, also in the inferotemporal cortex (ITC) in the ventral visual stream. Moreover, CIP inactivation caused a perceptual deficit in a depth-structure categorization task. CIP-microstimulation during fMRI further suggests that CIP projects via posterior parietal areas to the ITC in the ventral stream. To our knowledge, these results provide the first causal evidence for the flow of visual 3D information from the dorsal stream to the ventral stream, and identify CIP as a key area for depth-structure processing. Thus, combining reversible inactivation and electrical microstimulation during fMRI provides a detailed view of the functional interactions between the two visual processing streams.
Highlights
The primate visual cortex consists of a large number of cortical areas that collaborate to compute neural representations of the external world
Reversible inactivation of a parietal area reduced the functional activations in other parietal areas, and in distantly separate brain areas such as the inferotemporal cortex
Depth-structure sensitivity was defined as a significant activation for the contrast [CS–CC]–[FS–FC], where CS = curved stereo, CC = curved control, FS = flat stereo, and FC = flat control (p < 0.05, family wise error [fwe] corrected for multiple comparisons); i.e., voxels that were more activated by curved surfaces than by flat surfaces presented at the same mean disparities
Summary
The primate visual cortex consists of a large number of cortical areas that collaborate to compute neural representations of the external world. Lesion studies have demonstrated that each visual processing stream is specialized [12,13] and can function— at least to some extent—independently of the other stream [14,15] Both anatomical [16] and functional [17,18,19] evidence strongly suggest that the dorsal and ventral stream interact during object vision, but no study has been able to show conclusively which information is transferred between the two streams
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