Pseudostereoscopic illusion caused by interhemispheric temporal disparity: clinical and experimental observations.

An extension of Pulfrich's pseudostereoscopic illusion to a situation without interocular disparity, ie, even under purely monocular circumstances, was clinically observed and experimentally produced. The perceived distortion of the movement of a swinging pendulum was found to depend on different combinations of interhemispheric disparity induced by selective prolongation of the conduction time from the nasal or temporal retina to the corresponding hemisphere. In patients, tumor pressure caused the slower conduction time. In normal subjects, neutral density filters covering different visual fields produced similar conduction delays under experimental conditions. Recording the visually evoked response from over each hemisphere provided an objective tool for demonstration and measurement of interhemispheric differences of retinocortical conduction times in various clinical and experimental setups.