Local and Global Properties of Motion Aftereffects

Abstract

The local motion adaptation at the basis of the motion aftereffect (MAE) can be expressed in a variety of ways, depending upon the structure of the test display (N J Wade, L Spillmann, M T Swanston Vision Research in press). This has been demonstrated with MAEs from induced motion: if adaptation is to two moving (Surround) gratings, an MAE is seen in the central grating if two gratings surround it, but in the flanking gratings when they are themselves surrounded in the test stimulus. We report two experiments in which the characteristics of the test display and of the local adaptation process have been examined. In experiment 1, five vertical gratings were presented during adaptation; the outermost and central gratings remained stationary and those flanking the centre moved laterally. The test display always consisted of three stationary gratings: either the central three or the lower three equivalent to the locations of the adaptation display. MAEs were only recorded in the Centre and not in the Surround, irrespective of whether the Centre or Surround had been exposed to motion during adaptation. MAEs in the Centre were in opposite directions, reflecting the influence of Surround adaptation. The influence of adapting motion in different directions was examined in experiment 2. The upper grating always received the same direction of motion during adaptation, and the lower grating was absent, stationary, or moving in the same or in the opposite direction. The results indicate that an MAE is visible in the upper grating only after differential adaptation between the upper and lower gratings.