Pin Yang¹, Geoffrey Bingham¹; ¹Indiana University Blomington

Human motion-in-depth (MID) perception is supported by two stereomotion mechanisms, Change in Disparity Over Time (CDOT) and Inter-Ocular Velocity Differences (IOVD), but whether they serve different functional roles in visually-guided-action remains unclear. We examined whether individuals who rely more on CDOT versus IOVD exhibit distinct visuomotor control strategies during reaching. 200 participants first completed relative-distance discrimination tasks, allowing us to classify them as CDOT-dominant, IOVD-dominant, or Combined observers. Then, 72 participants (24 per group) performed dynamic reaching tasks using random-dot targets and hand avatars with constant size and dot-density, removing monocular information. Dotlife (1/2/8/16 frames, and infinite) was also manipulated to vary the temporal coherence of the MID signal. We found clear dissociations in visuomotor control as a function of stereomotion-channel dominance. Specifically, group effect on movement-time (F (2, 69) = 11.949, p < 0.001), reaching-accuracy (F (2, 69) = 10.583, p < 0.001), peak velocity (F (2, 69) = 8.152, p < 0.001) are all significant. CDOT-dominant observers showed slower velocities and longer movement times, consistent with CDOT’s role as a slow-motion processing channel. IOVD-dominant observers reached faster but with reduced mapping accuracy, reflecting a velocity-based strategy tuned to rapid yet less spatially precise targeting. Combined observers exhibited a hybrid profile, matching the IOVD group in reaching speed but the CDOT group in spatial accuracy. Dotlife manipulations highlighted these dissociations: Mapping accuracy in the CDOT group remained unaffected across dotlife conditions (F (4,92) = 1.94, p = 0.11); the IOVD group showed a significant improvement in accuracy from 1-frame to 2-frame dotlife, with no additional gains at longer dotlifes (F (4,92) = 6.4, p < 0.001). Together, these findings show that stereomotion-channel specialization influences both MID perception and visuomotor strategy used to visually guide action, underscoring the need to account for online guidance and individual differences in visuomotor models.