Adaptation to tilt is not produced by eye-muscle potentiation

The role of eye-muscle potentiation in adaptation to prismatic tilt was evaluated by assessing the presence of cyclotorsion induced by prolonged wearing of tilting prisms. Fundus photographs, containing the retinal image of the test line adjusted to the subjective vertical, were obtained before and after prism viewing that induced a 6 degrees aftereffect. The angular separation of the retinal images of the test line between pre- and post-prism photographs matched, in all cases, the difference in orientation between pre- and post-prism adjustment of the test line to the vertical. The data, therefore, clearly show that the eye is in exactly the same orbital position before and after substantial tilt aftereffects are induced. These results argue against the eye-muscle potentiation explanation of tilt aftereffects, that is, the explanation which says that tilt aftereffects are the result of prism induced changes in cyclotorsion.