MOTION AFTER-EFFECT DUE TO BINOCULAR SUM OF ADAPTATION TO LINEAR MOTION

The motion after-effect (MAE) can be elicited by adapting observers to global motion of randomly distributed dots before the!: view a displa y containing dots moving in random directions, but no global motion. E xperiments by others have shown that if the adaptation stimulus contai ns two directions of motion, the MAE points opposite to the vector sum of the adapting directions. The present study investigated whether su ch vector addition in the MAE could also occur if the two directions o f motion were presented to separate eyes. Observers were adapted to di fferent, but not opposite, directions of motion in the two eyes. Eithe r the left eye, the right eye, or both eyes were tested. Observers rep orted the direction of perceived motion during the test. When they saw the test stimulus with both eyes, observers reported seeing motion in the direction opposite that of the Vector sum of the adaptation direc tions. In the monocular test conditions observers reported MAE directi ons opposite to the corresponding monocular adaptation directions. In a second experiment we Verified that subjects had interocular transfer of the MAE. Together these results are consistent with a model in whi ch (I) addition of adaptation directions occurs at a binocular site, ( 2) directional adaptation occurs at a monocular site; and (3) monocula r adaptation is able to change the threshold for obtaining an MAE at t he binocular site, thus acting like binocular adaptation in interocula r transfer of the MAE. (C) 1998 Elsevier Science Ltd. All rights reser ved.