Temporal aspects of spatial adaptation. A study of the tilt aftereffect.

Growth and decay characteristics of the tilt aftereffect were studied for aftereffects induced by normal or continuous adaptation routines, and for aftereffects induced by successive or spaced adaptation to the same or different orientations on an adapt-partial decay-readapt schedule. In the continuous adaptation condition, growth and decay of the aftereffect were logarithmic functions of time. There was no evidence for saturation after 30 min adaptation. Aftereffect decay following spaced adaptation progresses as by continuous adaptation, but an adapting stimulus introduced during recovery from previous adaptation is more effective on the time scale than when introduced to a fully recovered system, summing approximately linearly with the residual aftereffect and off-setting the recovery process to zero. A second adapting stimulus whose orientation is of opposite sign (ccw vs cw) induces a two-phased decay process consisting of an early cancellation and a later enhancement of the original aftereffect. A two-stage model of adaptation is proposed.