Eye proprioception and visual localization in humans: influence of ocular dominance and visual context

It has been previously established that the application of low amplitude mechanical vibrations to the inferior rectus muscle of human subjects results in an illusory upward movement of a luminous spot fixated in total darkness, and in a corresponding overshooting of the target when the subject is asked to point to this spot. In the first experiment described here, we compared the effects of applying vibrations to each eye separately and to both eyes simultaneously, under monocular and binocular viewing conditions, in left- and right-eyed subjects. The results confirmed that proprioceptive signals arising from both eyes are involved in egocentric visual localization. A proprioceptive dominance was observed however since vibration of the dominant eye gave rise to larger pointing displacements. In addition, whichever eye was stimulated, the pointing shift induced by vibrating a covered eye was of smaller amplitude than that which occurred when vibrations were applied to the viewing eye. The second experiment showed that both the vibration induced illusions and the pointing shifts disappeared in a structured visual context, which suggests that the processes involved when the target is viewed in darkness might differ from those occurring in structured surroundings.