Perceived Movement in Depth as a Function of Stimulus Size

Abstract

The ability of subjects to perceive movement in depth of flat, circular luminous objects of various angular subtenses in an otherwise stimulus free field has been studied. The stimulus object bad a luminance of 1 ft-Lambert and varied in angular size from 1.5 to 60' of arc at the onset of movement. A method of constant stimuli was used to determine threshold values for the perception of movement. Accuracy in reporting direction of movement improved as the angular subtense of the stimulus increased. For stimuli with subtenses of 1.5 and 60' of arc the 75 per cent thresholds of perceived movement were 8 and 2 per cent change in angular size, respectively. A break in this function was found in the vicinity of stimulus sizes of 12' of are which indicates the possibility of two mechanisms involved in perceiving movement in depth.