A re-examination of the response latency theory on the Pulfrich phenomenon

Abstract

We re-examined the classical response latency theory by proposing a new theory based on response frequencies, which should increase with the amount of stimulation. The binocular system would determine the target's motion in depth by comparing two response frequencies in each monocular eye system. The subject observed dichoptically two targets, which were oscilating in the horizontal direction, concomitantly with each other. All targets were of the same luminance. In Experiment 1, one target was smaller than the other. The smaller the former was, the deeper the superimposed target appeared to swing, as predicted by our frequency theory. But when the former became too small, the depth appeared to decrease. In Experiment 2, one target was presented intermittently while the other was presented continuously. The less frequently the former was presented, the deeper the superimposed target appeared to swing, again as predicted by our frequency theory. Because the Pulfrich phenomenon appeared even when the two targets were of the same luminance, the response latency theory was proven to be insufficient. Some physiological speculations were added.