Binocularity of early motion mechanisms: comments on Georgeson and Shackleton.

The demonstration of compelling dichoptic illusions of motion using a variety of stimuli, all of which share the property that left and right eye patterns were spatio-temporal quadrature pairs, has been interpreted as evidence for binocular integration in the early motion system (short range motion). Georgeson and Shackleton (1989, Vision Research, 29, 1511-1523) have recently challenged this position based on results using 3 types of stimuli, sinusoidal gratings, random line kinematograms and missing fundamental squarewaves. For each class of stimuli motion was perceived during dichoptic presentation, but certain limitations led them to conclude that early motion mechanisms are defeated when no motion is present monocularly. We do not dispute their data, rather an alternative interpretation is offered which supports the position that early motion sensors are capable of binocular integration, a property well established physiologically.