Local versus global and retinotopic versus non-retinotopic motion processing in schizophrenia

Schizophrenia impairs cognitive function as much as perception. For example, patients perceive global motion in random dot kinematograms less strongly, because the integration of the dots into a single Gestalt is complex (e.g., Chen, Nakayama, Levy, Matthysse, & Holzman, 2003). Similarly, the perception of apparent motion is impaired, because the filling in of the illusory trajectory requires complex processing (Saucer & Deabler, 1956). Here, we investigated very complex motion processing using the Ternus-Pikler apparent motion display. First, we tested whether the perception of global apparent motion is impaired in schizophrenics compared to healthy controls. The task required both the grouping of multiple objects into a coherent Gestalt and the filling in of its illusory motion trajectory. Second, we tested the perception of rotation in the same stimulus, which in addition required the computation of non-retinotopic motion. Contrary to earlier studies, patients were not impaired in either task and even tended to perform better than controls. We argue that deficient neuromodulation, rather than motion processing deficits, explains the differences observed in previous studies.