Dynamics of walking adaptation aftereffects induced in static images of walking actors.

Visual adaptation to walking actions results in subsequent aftereffects that bias perception of static images of walkers in different postures so that they are interpreted as walking in the opposite direction to the adapting actor. It is not clear, however, if the walking aftereffect is comparable to other well studied low- and high-level visual aftereffects. We therefore measured the dynamics of the walking aftereffect in order to assess the characteristics of the adapting mechanism. We found that walking aftereffects showed similar characteristic dynamics as for face aftereffects and some motion aftereffects. Walking aftereffects could be induced in a broad range of different static images of walking actors and were not restricted to images of actors in any particular posture. Walking aftereffects increased with adapting stimulus repetition and declined over time. The duration of the aftereffect was dependent upon time spent observing the adapting stimulus and could be well modelled by a power-law function that characterises this relationship in both face and motion aftereffects. Increasing the speed of the adapting stimulus by increasing actor walk speed increased aftereffect magnitude, as seen for some motion aftereffects. The nature of the aftereffects induced by observing walking actors indicates that they behave like traditional high-level visual aftereffects.