Simulation of artificial vision: I. Eccentric reading of isolated words, and perceptual learning

Simulations of artificial vision were performed to assess “minimum requirements for useful artificial vision”. Retinal prostheses will be implanted at a fixed (and probably eccentric) location of the retina. To mimic this condition on normal observers, we projected stimuli of various sizes and conte...

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Bibliographic Details
Published in:	Vision research (Oxford) Vol. 43; no. 3; pp. 269 - 283
Main Authors:	Sommerhalder, Jörg, Oueghlani, Evelyne, Bagnoud, Marc, Leonards, Ute, Safran, Avinoam B, Pelizzone, Marco
Format:	Journal Article
Language:	English
Published:	Oxford Elsevier Ltd 01-02-2003 Elsevier Science
Subjects:	Adult Biological and medical sciences Blindness - rehabilitation Eccentric reading Fundamental and applied biological sciences. Psychology Humans Language Learning Learning - physiology Middle Aged Pattern Recognition, Visual Perception Photic Stimulation - methods Production and perception of written language Prostheses and Implants Prosthesis Design Psychology. Psychoanalysis. Psychiatry Psychology. Psychophysiology Reading Reading performance Recognition (Psychology) - physiology Retina - physiology Simulation Vision Vision, Binocular - physiology Vision, Monocular - physiology Visual Fields - physiology Visual prosthesis Learning Eccentric reading Simulation Visual prosthesis Reading performance Human Reading Eccentricity Artificial vision Perception Perceptive learning Experimental study
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Summary:	Simulations of artificial vision were performed to assess “minimum requirements for useful artificial vision”. Retinal prostheses will be implanted at a fixed (and probably eccentric) location of the retina. To mimic this condition on normal observers, we projected stimuli of various sizes and content on a defined stabilised area of the visual field. In experiment 1, we asked subjects to read isolated 4-letter words presented at various degrees of pixelisation and at various eccentricities. Reading performance dropped abruptly when the number of pixels was reduced below a certain threshold. For central reading, a viewing area containing about 300 pixels was necessary for close to perfect reading (>90% correctly read words). At eccentricities beyond 10°, close to perfect reading was never achieved even if more than 300 pixels were used. A control experiment using isolated letter recognition in the same conditions suggested that lower reading performance at high eccentricity was in part due to the “crowding effect”. In experiment 2, we investigated whether the task of eccentric reading under such specific conditions could be improved by training. Two subjects, naive to this task, were trained to read pixelised 4-letter words presented at 15° eccentricity. Reading performance of both subjects increased impressively throughout the experiment. Low initial reading scores (range 6%–23% correct) improved impressively (range 64%–85% correct) after about one month of training (about 1 h/day). Control tests demonstrated that the learning process consisted essentially in an adaptation to use an eccentric area of the retina for reading. These results indicate that functional retinal implants consisting of more than 300 stimulation contacts will be needed. They might successfully restore some reading abilities in blind patients, even if they have to be placed outside the foveal area. Reaching optimal performance may, however, require a significant adaptation process.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	0042-6989 1878-5646
DOI:	10.1016/S0042-6989(02)00481-9