Spatial localization with paralyzed eye muscles.

Four subjects suffering from a unilateral peripheral paralysis of the 3rd or the 6th nerves have been studied in spatial localization tasks, with their normal eye occluded. When peripheral targets were presented in the hemifield corresponding to the paralysis, the saccadic eye movements (recorded from the normal occluded eye) were of an exaggerated amplitude. 'Staircase' oculomotor patterns, closely similar to those occurring in 'open-loop' visual stimulation, could also be observed. Our patients also presented the classical hypermetric misreaching when attempting to point by hand at visual targets in an otherwise dark room. This effect (past-pointing) was likely to be due to a monitoring of the exaggerated oculomotor signal: in one subject past-pointing disappeared when reaching at the targets on the basis of the sole retinal cues. Finally, the classically described illusory visual effects of ocular paralysis were limited to a feeling of instability during self-motion.