Abstract
Purpose. Binocular disparity is one of the most powerful sources of depth information. Stereomotion (SM) is motion in depth generating by changing disparity over time. We ask whether SM is processed in (i) disparity-selective areas, (ii) motion- selective areas, (iii) in both disparity and motion areas, or (iv) in some specialized SM area?
Methods. The processing of SM in human visual cortex was studied with BOLD functional magnetic resonance imaging (fMRI). Dynamic autostereograms alternating between two disparity-determined depth planes produced the SM stimulation. SM was compared with: (1) stationary disparity planes, (2) lateral-motion at the horopter, (3) disparate lateral motion (DLM). The BOLD responses were collected on a GE Signa 3T scanner in 22 near-coronal slices spanning the posterior half of the brain. The test-null stimuli were alternated for 9s each in 8 blocks, totaling 144 s plus a fixation period.
Results. The main activity in all comparisons occupied regions inside MT/MST motion complex, with very little SM activation elsewhere. The posterior part of this complex could be subdivided into a region completely unresponsive to SM and an adjacent region responding preferentially to SM. The extension of the areas of differential activity sharply decreased from SM vs. disparity, through SM vs. lateral motion, to SM vs. DLM. In addition to V5+ response, an area purely responsive to SM vs. DLM was found in the temporal lobe anterior to the V5+ complex.
Conclusions. The results show a role of MT/MST complex in stereomotion processing. Within MT/MST, the data suggest segregated encoding of the direction of motion in the 3D space.