Reading with a simulated 60-channel implant

• Main Authors: Angelica ePerez Fornos, Jörg Rudolph Sommerhalder, Marco ePelizzone
• Format: Article
• Language: English
• Published: Frontiers Media S.A. 2011-05-01
• Series: Frontiers in Neuroscience
• Subjects: Psychophysics; Neuroscience; Resolution; Spatial Vision; reading; field of view
• Online Access: http://journal.frontiersin.org/Journal/10.3389/fnins.2011.00057/full

First generation retinal prostheses containing 50-60 electrodes are currently in clinical trials. The purpose of this study was to evaluate the theoretical upper limit (best possible) reading performance attainable with a state-of-the-art 60-channel retinal implant and to find the optimum viewing conditions for the task. Four normal volunteers performed full-page text reading tasks with a low resolution, 60-pixel viewing window that was stabilized in the central visual field. Two parameters were systematically varied: (1) spatial resolution (image magnification) and (2) the orientation of the rectangular viewing window. Performance was measured in terms of reading accuracy (% of correctly read words) and reading rates (words/min). Maximum reading performances were reached at spatial resolutions between 3.6 and 6 pixels/char. Performance declined outside this range for all subjects. In optimum viewing conditions (4.5 pixels/char), subjects achieved almost perfect reading accuracy and mean reading rates of 26 words/min for the vertical viewing window and of 34 words/min for the horizontal viewing window. These results suggest that, theoretically, some reading abilities can be restored with actual state-of-the-art retinal implant prototypes if image magnification is within an optimum range. Future retinal implants providing higher pixel resolutions, thus allowing for a wider visual span might allow faster reading rates.