Schizophrenia (Sz) is a mental health disorder characterized by severe cognitive, emotional, social, and perceptual deficits. Visual deficits are found in tasks relying on the magnocellular/dorsal stream. In our first experiment we established deficits in global motion processing in Sz patients compared to healthy controls. We used a novel task in which background optic flow produces a distortion of the apparent trajectory of a moving stimulus, leading control participants to provide biased estimates of the true motion trajectory under conditions of global stimulation. Sz patients were significantly less affected by
the global background motion, and reported trajectories that were more veridically accurate than those of controls. In order to study the mechanism of this effect, we performed a second experiment where we applied transcranial electrical stimulation over area MT+ to selectively modify global motion processing of optic flow displays in healthy participants. Cathodal and high frequency random noise stimulation had opposite effects on trajectory perception in optic flow. The brain stimulation over a control site and in a control task revealed that the effect of stimulation was specific for global motion processing in area MT+. These findings both support prior studies of impaired early visual processing in Sz and provide novel approaches for measurement and manipulation of the underlying circuits.