Mechanisms for discrimination following adaptation to radial motion

It is well known that adaptation to expanding and contracting motion flow fields results in a motion aftereffect (MAE), making motion-­balanced patterns to appear to be moving in the direction opposite the adaptor. Integration of motion directions in test stimuli presented next to each other could interfere with global processing. Here we show that adaptation affects sensitivity to small differences in motion coherence, and compare performance on a temporal versus spatial two-­alternative forced choice task. Two fields of dots were presented, either simultaneously as two hemifields (s2AFC), or sequentially in two intervals (t2AFC). One stimulus consisted of a pedestal dot coherence level, while the other contained an additional increment in coherence. Three pedestals were tested, 0, 0.5, 1 and 2 times the subjects’ detection threshold. Following adaptation in both hemifields, subjects decided which of two fields of dots contained more coherent (expanding/contracting) motion. Sensitivity at the zeropedestal is reduced by an average of 58% following adaptation, with significant intersubject variability. Discrimination performance of a motion increment at higher pedestals is not significantly affected.