Minimum Requirements for Visuomotor Coordination and Learning of Such Tasks in Eccentric Vision

Abstract

Abstract: : Purpose: Determination of the minimum requirements for a visual prosthesis to restore useful visuomotor coordination abilities and evaluation of learning effects when performing such tasks in eccentric vision. Methods:Normal subjects were requested to complete 2 visuomotor coordination tasks: pointing on random targets as accurately as possible (leds task) and placing wooden chips according to a given pattern (chips task). Five image resolution levels (17920, 1991, 498, 221, and 124 pixels) and 3 effective viewing angles (8.3°x6°, 16.5°x11.6°, and 33°x23.1°) were displayed on a 10°x7° viewing area, stabilized at a fixed position in the visual field. First, the minimum requirements needed to reach optimum performance were established using central vision. Then 3 normal volunteers, naïve to eccentric viewing, were trained to perform both tasks using a viewing area at 15° of eccentricity in the lower visual field. Results:Using central vision, visuomotor coordination performance decreased significantly (p<0.05) for effective image resolutions below 2 pixel/deg². Above this threshold, subjects performed the tasks more rapidly with the largest viewing angle. Our measurements indicated that the intermediate viewing angle (16.5°x11.6°) was the best compromise and subjects spontaneously reported preferring it to the others. Based on these results, a 16.5°x11.6° viewing angle containing 498 pixels (2.6 pixel/deg²) was chosen for training in eccentric viewing conditions. Subjects adapted quite rapidly to eccentric viewing. Precision increased and asymptoted within the first 10 training sessions. Time to perform the tasks stabilized after about 15 sessions. Conclusions: Compared to the reading task, these results confirm that visuomotor coordination is less demanding in terms of visual information content. We therefore estimate that about 500 distinctly perceived phosphenes, distributed on a 2x3 mm² implant, remain the minimum criterion to achieve useful reading, visuomotor coordination, and mobility.

Keywords: pattern vision • space and scene perception • learning