EYE PROPRIOCEPTION AND VISUAL LOCALIZATION IN HUMANS - INFLUENCE OF OCULAR DOMINANCE AND VISUAL CONTEXT

It has been previously established that the application of low amplitu de mechanical vibrations to the inferior rectus muscle of human subjec ts results in an illusory upward movement of a luminous spot fixated i n total darkness, and in a corresponding overshooting of the target wh en the subject is asked to point to this spot. In the first experiment described here, we compared the effects of applying vibrations to eac h eye separately and to both eyes simultaneously, under monocular and binocular viewing conditions, in left- and right-eyed subjects. The re sults confirmed that proprioceptive signals arising from both eyes are involved in egocentric visual localization. A proprioceptive dominanc e was observed however since vibration of the dominant eye gave rise t o larger pointing displacements. In addition, whichever eye was stimul ated, the pointing shift induced by vibrating a covered eye was of sma ller amplitude than that which occurred when vibrations were applied t o the viewing eye. The second experiment showed that both the vibratio n induced illusions and the pointing shifts disappeared in a structure d visual context, which suggests that the processes involved when the target is viewed in darkness might differ from those occurring in stru ctured surroundings.