Neuropsychological evidence of hig-level processing in Binocular Rivalry

During binocular rivalry, two incompatible images presented one to each eye spontaneously alternate in visual consciousness. This phenomenon is explained by competition between neural representations of the images at various levels in the brain, from the earliest parts of the visual system at which binocular convergence occurs (V1) to much higher parts (such as the frontal lobes). To investigate level of processing, we manipulated stimulus complexity and measured rivalry in brain-damaged patients with unilateral spatial neglect (USN) from lesions to parietal and frontal lobes. We tested 10 neurologically unimpaired people, 9 right-brain-damaged patients with USN, and 12 right-brain-damaged patients without USN. Participants pressed one of two buttons to track their experience of rivalry over one-minute displays of stimuli differing in complexity: gratings with different orientations (simple), gratings with different spatial frequencies (simple), two different configurations of illusory motion (more complex), and two different objects (most complex). We found in the neurologically unimpaired participants that the rivalry alternation rate was slower for more complex stimuli. In the brain-damaged patients, alternation rates were lower than controls and no effect of stimulus complexity emerged. Because our patients’ brain damage is confined to parietal and frontal lobes, we conclude that processing within these areas of the brain influences the temporal course of visual consciousness.