The Relation between the Thresholds of Form, Motion, and Displacement in Parafoveal and Peripheral Vision at a Scotopic Level of Illumination

Abstract

Although a vast amount of research has been done in the general field of vision, very little systematic work has been concerned with the problems of the perception of motion. Such studies as have appeared on acuity for motion have been limited largely to photopic levels of illumination in the foveal and parafoveal regions. Numerous studies have centered on the problems of apparent rather than real motion. This line of investigation is exemplified in the work of Wertheimer and others.1 Reviews of the literature on the perception of motion may be found in articles by Klein2 and Kennedy.3 The present experiment is concerned with a comparison of the thresholds of form, motion, and displacement, using the same type of stimulus throughout. The threshold of form, which is equivalent here to the minimum separable index of visual acuity, is measured by the smallest separation of two contours which can be recognized as discrete. The threshold of motion was taken as the slowest perceptible rate of movement of the stimulus. The threshold of displacement was considered to be the minimum distance through which the stimulus-object moved at a given speed in order to give a perception of movement.