A frequent consequence of strabismus and amblyopia is a loss of normal binocular functions. Under binocular viewing conditions, many individuals with these disorders are essentially monocular. Attempts to improve or restore binocular function in such individuals are hampered by chronic suppression of the weaker eye. Preliminary investigations (Nei R03-04297-01) have uncovered a way to disrupt suppression in normal and binocularly abnormal individuals. Suppression, in the form of binocular rivalry, is produced whenever different stimuli are presented to corresponding points in each eye. At any instant, a normal observer will see only one of the monocular stimuli at each location in the visual field. Observers with chronic suppression will see only the stimulus in the dominant eye. However, when briefly or intermittently presented, dichoptic stimuli appear to fuse. I have discovered that this 'abnormal fusion' is seen by many stereoblind subjects. The processes underlying this abnormal fusion are not understood and the potential uses of abnormal fusion in the treatment of impaired binocular vision have not been explored. The proposed research has four aims: A) to describe the process responsible for abnormal fusion in normal subjects, B) to describe the function of that process in normal vision, C) to examine changes in that process accompanying the binocular abnormalities that lead to stereoblindness and chronic suppression, and D) to determine if we can use knowledge about such a process to enhance the binocular capabilities of binocularly impaired individuals.