LOCAL VELOCITY REPRESENTATION - EVIDENCE FROM MOTION ADAPTATION

Adaptation to a moving visual pattern induces shifts in the perceived motion of subsequently viewed moving patterns. Explanations of such ef fects are typically based on adaptation-induced sensitivity changes in spatio-temporal frequency tuned mechanisms (STFMs). An alternative hy pothesis is that adaptation occurs in mechanisms that independently en code direction and speed (DSMs). Yet a third possibility is that adapt ation occurrs in mechanisms that encode 2D pattern velocity (VMs). We performed a series of psychophysical experiments to examine prediction s made by each of the three hypotheses. The results indicate that: (1) adaptation-induced shifts are relatively independent of spatial patte rn of both adapting and test stimuli; (2) the shift in perceived direc tion of motion of a plaid stimulus after adaptation to a grating indic ates a shift in the motion of the plaid pattern, and not a shift in th e motion of the plaid components: and (3) the 2D pattern of shift in p erceived velocity radiates away from the adaptation velocity; and is i nseparable in speed and direction of motion. Taken together, these res ults are most consistent with the VM adaptation hypothesis. (C) 1998 E lsevier Science Ltd. All rights reserved.