The Pulfrich Effect, Simple Reaction Time, and Intensity Discrimination

Abstract

The present study is part of a long-range research program on the effects of conditions of illumination on visual latenc y, as measured by several different monocular and binocular experimental procedures. It is an extension of an earlier stud y reported by Lit (1949), in which the magnitudes of the near and far displacements of the Pulfrich stereophenomenon were measured at various levels of illumination. The Pulfrich effect occurs when a target oscillating in the observer ’ s frontal plane is viewed under conditions of unequal binocular illumination (Pulfrich, 1922). The oscillating target will then appear to rotate out of its plane of oscillation: the target will appear to be displaced in front of its actual plane of oscillation (near displacement) for one direction of target stroke and behind the plane of oscillation (far displacement) for the return stroke. The apparent displacements in depth were accounted for in terms of a h ypothetical visual latenc y whose magnitude was inversely related to level of illumination (Pulfrich, 1922). Lit (1949) has presented a geometric analysis of the Pulfrich effect, including a detailed derivation of the equations that convert the near and far displace