Visual Latency Difference Determined by Two ‘‘Rotating’’ Pulfrich Techniques

Abstract

We tested the validity of Nickalls’ formula for determining visual latency difference by using two rotating Pulfrich techniques: (A) varying viewing distance while keeping target angular velocity constant (33 rev/min) and (B) varying the target angular velocity while keeping the viewing distance constant (180 cm). The formula predicts that the latency differences estimated by the two techniques are equal with a given neutral density filter. Observers were asked to judge whether or not the rotating target (clockwise) appeared to move back-and-forth from side-to-side with a neutral density filter (OD = 0.7, 1.0, 1.3) in front of the right eye. The results with ten observers showed that the mean visual latency differences associated with each technique for a given filter were not significantly different. These results further validate the Nickalls’ formula and, therefore, support the visual-latency hypothesis to account for the Pulfrich phenomenon.