Authors:
J. D. Dorn, A. K. Ahuja, A. Caspi1, E. Filley, G. Dagnelie, R. J. Greenberg, M. J. Mcmahon
Summary:
Purpose - The feasibility of the Argus™ II 60 electrode epi-retinal system to partially restore vision to subjects blinded by Retinitis Pigmentosa is currently under investigation in several clinical centers worldwide. The purpose of this work was to test whether the system provided spatially distinct information through multi-electrode stimulation, allowing subjects to determine the direction of motion of an object in the visual field.
Methods - The Argus™ II retinal prosthesis consists of an array of 60 independent electrodes. The stimulation current of each electrode is determined by the brightness at the corresponding area of the scene captured in real-time by a camera mounted on the subjects’ glasses. Subjects maintained eye and head fixation on the center of a 19” touchscreen monitor placed 12” in front of them. After an audio prompt, a 1.4” wide white line swept across the black monitor screen at a randomly chosen angle (0-360°). The speed of the motion was fixed throughout the experiment but varied across subjects. After each trial, the subjects drew the direction of motion they perceived on the touchscreen. An experiment consisted of 80 trials with automated verbal feedback. The experiment was run in three conditions: with the subjects’ native vision alone (system off), with the system on and normal spatial mapping of the video image to the electrodes, and with the system on and scrambled spatial mapping between the image and the electrodes (as a control condition, Caspi et al., 2009).
Results - The error (difference between the direction of the moving line and the direction drawn) was calculated for each trial. Ten out of 15 subjects had smaller average error with the system on than with their native vision alone (t-test, p<0.05). Of these, 7 of the 8 subjects that were available for further testing had significantly smaller average error with a normal spatial mapping than with a scrambled spatial mapping. Four subjects showed no difference in the results when performing the task with the system on (and normal spatial mapping) compared to performing the task with their native vision alone (system off), and one subject had better performance when the system was off, due to residual native vision.
Conclusions - The Argus™ II retinal prosthesis improved the ability of most blind subjects (10 out of 15) to identify the direction of a moving object. This work demonstrates that the system provides spatio-temporal information from multiple stimulating electrodes that can be used to perform perceptual tasks.
Source:
Presented at Neuroscience 2009, the annual meeting of the Society for Neuroscience. Scientific Presentation: Sunday, Oct. 18, 2:15–2:30 p.m., Room N228