Effects of tilt adaptation on the direction of voluntary saccades.

Records were taken of the horizontal and vertical amplitudes of eye moments of subjects instructed to move their eyes back and forth from 12 to 6 and from 9 to 3 o'clock without targets. These records were used to compute the angles of the eye-moment paths, and corresponding paths were compared before and after exposure in a hallway to a prism-induced clockwise tilt of 30 degrees. Perceived orientation was also measured, by having the subjects set a luminous line in the dark to the orientations indicated above. Both tasks yielded significant preexposure-postexposure changes in the direction of tilt, such that after exposure the line was set at a tilt and eye movements were made at an angle clockwise with respect to the preexposure orientation. A control group exposed to 0 degrees tilt showed no change on either task. Thus, tilt adaptation is capable of altering the direction of volitional eye movements.