Resolving motion–position conflict: dorsal–ventral interactions during illusory jitter perception

Motion-induced spatial conflict occurs when an isoluminant boundary moves smoothly near a moving luminance-defined boundary: observers perceive spatial jitter superimposed on the otherwise smooth trajectory, despite the absence of physical jitter. This phenomenon shows that perceived object location can fluctuate even when the retinal trajectory is smooth. Because motion-related and form-related visual information is processed across partially distinct dorsal and ventral visual systems, this phenomenon provides a model for examining cross-stream interactions. However, the cortical mechanisms underlying this illusion remain unclear. Here, we used functional MRI to test whether motion-induced spatial conflict is associated with dorsal-ventral network interactions by comparing an illusory jitter condition, a luminance-defined no-jitter control condition, and a physical-jitter control condition. Whole-brain analyses revealed widespread lower BOLD responses in the illusion condition relative to both control conditions, with overlapping effects involving the inferior parietal lobule (IPL) and inferotemporal cortex (IT). Critically, beta-series functional coupling between IPL and IT was enhanced during the illusion. An exploratory Granger-causality analysis further suggested an asymmetry in within-trial BOLD dynamics, with larger IPL→IT than IT→IPL Granger-predictive effects. Complementing these condition-level network effects, exploratory within-condition analyses provided supportive evidence that trial-wise regional activity within the IPL-IT network, most consistently in IPL, varied with subjective jitter perception under physically identical illusory trials. These findings suggest that motion-induced spatial conflict is associated with altered IPL-IT interactions, highlighting parietal-temporal coupling as a candidate network process involved in distortions of perceived object location.