Induced stereoscopic motion (ISM) is illusory depth-motion in a fixed- disparity target induced by stereomotion (SM) in its surround (JOV 2003); SM is depth-motion generated by disparity changes. We have previously reported a network of brain areas involved in SM processing. In this study we ask whether ISM and “true” SM rely on common or separate cortical mechanisms. The stimuli were dynamic autostereograms consisting of a target and a surround. fMRI responses were obtained on a GE Signa 3T scanner with spiral acquisition in 23 coronal slices at a resolution of 3mm^3 and a TR of 3s. Test and null stimuli alternated for 9s each in 36 blocks per scan. An attention control task was also performed throughout each scan. First, we mapped the retinotopic specification for “true” SM in the target area. In the second experiment ISM was induced in the fixed-disparity target. Both SM and ISM were contrasted with static null-stimuli. In two additional control experiments SM and ISM were each contrasted with X-lateral motions, instead of static images, in order to entirely dissociate their Z-direction from any lateral component. The retinotopic areas and the motion area were identified in separate localizer scans. ISM activates the higher areas of the SM-network including a subregion in hMT+, foveal V3A, V7 and caudal IPS, but less strongly than SM itself. However ISM did not activate the early retinotopic areas of the SM-network (V1, V2). Thus, the global contextual interactions required for the induction of ISM seem to happen later in the processing stream, beyond the early retinotopic areas.

Supported by EY 7890.