He [Albert Einstein] seemed also to relish his intellectual and social exchanges with [his friend, Gestalt psychologist Max] Wertheimer. Wertheimer was once amused when he and Einstein consecutively covered their right and left eyes with their hands to test the effects of retinal disparity (the slightly different images of the same object on the two retinas because of the spatial separation of the eyes) as they stared at a church steeple. Watching these figures on the street corner, a crowd soon gathered and the two were surprised to see that the onlookers were also engaging in this curious behavior, shifting their hands back and forth over their eyes. more>>>
