Retinal prostheses, which restore partial vision to patients blinded by outer retinal degeneration, are currently in clinical trial. The Argus II retinal prosthesis system was recently awarded CE approval for commercial use in Europe. While retinal prosthesis users have achieved remarkable visual improvement to the point of reading letters and short sentences, the reading process is still fairly cumbersome. This study investigates the possibility of using an epiretinal prosthesis to stimulate visual braille as a sensory substitution for reading written letters and words. The Argus II retinal prosthesis system, used in this study, includes a 10 × 6 electrode array implanted epiretinally, a tiny video camera mounted on a pair of glasses, and a wearable computer that processes the video and determines the stimulation current of each electrode in real time. In the braille reading system, individual letters are created by a subset of dots from a 3 by 2 array of six dots. For the visual braille experiment, a grid of six electrodes was chosen out of the 10 × 6 Argus II array. Groups of these electrodes were then directly stimulated (bypassing the camera) to create visual percepts of individual braille letters. Experiments were performed in a single subject. Single letters were stimulated in an alternative forced choice (AFC) paradigm, and short 2–4-letter words were stimulated (one letter at a time) in an open-choice reading paradigm. The subject correctly identified 89% of single letters, 80% of 2-letter, 60% of 3-letter, and 70% of 4-letter words. This work suggests that text can successfully be stimulated and read as visual braille in retinal prosthesis patients.
Keywords: retina, epiretinal prosthesis, sensory substitution, retinitis pigmentosa, blindness, perception, degeneration, sight restoration
Citation: Lauritzen TZ, Harris J, Mohand-Said S, Sahel JA, Dorn JD, McClure K and Greenberg RJ (2012) Reading visual braille with a retinal prosthesis. Front. Neurosci. 6:168. doi: 10.3389/fnins.2012.00168
Received: 07 July 2012; Accepted: 01 November 2012;
Published online: 22 November 2012.
Edited by:John P. Donoghue, Brown University, USA
Reviewed by:Silvestro Micera, Scuola Superiore Sant’Anna, Italy
Copyright: © 2012 Lauritzen, Harris, Mohand-Said, Sahel, Dorn, McClure and Greenberg. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in other forums, provided the original authors and source are credited and subject to any copyright notices concerning any third-party graphics etc.
*Correspondence: Thomas Z. Lauritzen, Second Sight Medical Products, 12744 San Fernando Road, Building 3, Sylmar, CA 91342, USA. e-mail: firstname.lastname@example.org