False reaching movements in localization test and effect of auditory feedback in simulated ultra-low vision subjects and patients with retinitis pigmentosa.

PURPOSE: To determine the accuracy of reaching movements with localization tests in subjects with simulated ultra-low vision, and to examine the effectiveness of auditory feedback training in improving the accuracy of the reaching movements.
METHODS: Twenty-one subjects with simulated ultra-low vision and three patients with advanced retinitis pigmentosa (RP) were studied with the localization tester. The localization tester had white square targets with a visual angle of 10° that were projected randomly on a computer monitor screen. The subjects or RP patients were instructed to touch the center of the target. Each subject was tested 20 trials. The distance from the center of the target to the point where subjects touched, the deviation, was calculated automatically by the computer. We also examined the effect of auditory feedback on improving the accuracy of reaching movements.
RESULTS: The average angle of deviation in the subjects was not significantly correlated with visual acuity. The points touched by subjects with simulated low vision were located downward and horizontally toward the hand they used. They were condensed around the barycenter of the touched points (paired t tests; *p = 0.037). The touched points of the patients also deviated downward and condensed around the barycenter. The deviations decreased significantly with auditory feedback when trained over 100 trials.
CONCLUSIONS: The subjects with simulated ultra-low vision and the advanced RP patients had false orientations against the position of localized target systematically. An auditory feedback system may help to correct the false orientations for reaching movements in patients with very low vision.