Human adaptation to rotated vision: interplay of a continuous and a discrete process.

The mechanisms for adaptation to visual rotation were investigated by exposing subjects to different rotation angles in a stepwise fashion. We found that response direction continuously changed to compensate for the imposed rotation, but this change was limited to 90 deg. Larger changes were accomplished by inverting both spatial axes (which is equivalent to a 180 deg rotation), and then gradually changing response direction "backwards" to the prescribed value. The angle of 0 deg had no such limiting value like 90 deg: Response direction could continuously change through 0 deg and beyond. Our data provided no evidence that adaptation to opposite-directed visual rotations results in interference, due to competition in working memory; instead subjects' performance under such conditions is fully explained by the said continuous changes of response direction. We conclude that adaptation is achieved by a coordinated interplay of continuous (gradual rotation between +/-90 deg) and discrete (sign reversal) processes.