The effect of implied motion on the motion after-effect

Abstract

Directional motion adaptation has previously been reported following exposure to sequences of unrelated still photographs depicting implied motion (‘implied motion after-effect’, IMAE; Winawer et al., 2008). To investigate the relationship between processes activated by implied motion and by explicit dynamic motion, we tested whether the IMAE can combine with the classical motion after-effect (CMAE) elicited by adaptation to drifting dot patterns. Participants adapted to stimuli which combined moving dot patterns with sequences of static implied-motion images. Motion adaptation was measured using a forced-choice staircase procedure in which the displacement of drifting test dots was varied to find the observer’s motion ‘null’ point. Following adaptation to combinations of still images and incoherently moving dots, the null point shifted by a small amount in the direction predicted by earlier IMAE reports. Adaptation to combinations of still images and coherently moving dots also affected the magnitude of the CMAE, consistent with a modulatory effect of implied motion on directional adaptation. These psychophysical results indicate that implied motion can influence adaptation in motion selective processes, but the underlying mechanism remains to be established.