Simulation of artificial vision: II. Eccentric reading of full-page text and the learning of this task

Abstract

Reading of isolated words in conditions mimicking artificial vision has been found to be a difficult but feasible task. In particular at relatively high eccentricities, a significant adaptation process was required to reach optimal performances [Vision Res. 43 (2003) 269]. The present study addressed the task of full-page reading, including page navigation under control of subject's own eye movements. Conditions of artificial vision mimicking a retinal implant were simulated by projecting stimuli with reduced information content (lines of pixelised text) onto a restricted and eccentric area of the retina. Three subjects, naïve to the task, were trained for almost two months (about 1 h/day) to read full-page texts. Subjects had to use their own eye movements to displace a 10 degrees x 7 degrees viewing window, stabilised at 15 degrees eccentricity in their lower visual field. Initial reading scores were very low for two subjects (about 13% correctly read words), and astonishingly high for the third subject (86% correctly read words). However, all of them significantly improved their performance with time, reaching close to perfect reading scores (ranging from 86% to 98% correct) at the end of the training process. Reading rates were as low as 1-5 words/min at the beginning of the experiment and increased significantly with time to 14-28 words/min. Qualitative text understanding was also estimated. We observed that reading scores of at least 85% correct were necessary to achieve 'good' text understanding. Gaze position recordings, made during the experimental sessions, demonstrated that the control of eye movements, especially the suppression of reflexive vertical saccades, constituted an important part of the overall adaptive learning process. Taken together, these results suggest that retinal implants might restore full-page text reading abilities to blind patients. About 600 stimulation contacts, distributed on an implant surface of 3 x 2 mm2, appear to be a minimum to allow for useful reading performance. A significant learning process will however be required to reach optimal performance with such devices, especially if they have to be placed outside the foveal area.

Image processing based recognition of images with a limited number of pixels using simulated prosthetic vision

“…Inspiring results were reported 0020-0255/$ -see front matter Ó 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.ins.2010.04.021 on Latin word recognition [24,25,34], Chinese character recognition [8], reading speed [5][6][7], text or paragraph reading [35,15,10], maze navigation [6], object recognition [19], hand-eye coordination [19], way finding [11], etc. However, it is important to confirm the minimum requirements for visual prostheses through different experiments.…”

Progress towards a high-resolution retinal prosthesis

“…Thus visual acuity at the level of 20/400 corresponds geometrically to a pixel size of about 100 µm, while acuity of 20/100 (sufficient for reading with some visual aids) requires pixels smaller than 25 µm. It has been previously estimated that *butterwick@stanford.edu; phone +1 (650) 723-0789; 445 Via Palou, Stanford, CA 94305 about 600 pixels is a minimum for resolving images in the central field [7] and for useful reading performance [8]. For functional restoration of sight the array should ideally cover a field of view of at least 10 o (which corresponds to a 3 mm diameter spot on the retina), and support a visual acuity of 20/100 (which corresponds to 1600 pixels/mm 2 ) in the central 2-3 o of stimulating area.…”

Dégénérescence des photorécepteurs: stratégies thérapeutiques et nouvelles perspectives

“…À l'inverse, un implant épi-rétinien, s'il présente l'avantage d'être moins invasif, fonctionne en stimulant directement les cellules ganglionnaires, l'information transmise nécessitera donc un codage dont les modalités sont cours de caractérisation. D'autres aspects essentiels de ces prothèses sont ceux de leur géométrie (Sommerhalder et al 2004) et de leur biocompatibilité. Des études sont actuellement en cours chez l'animal pour évaluer l'effet des stimulations électriques sur le réseau neuronal in vivo et in vitro (Stett et al 2000 ;Salzmann et al 2006 ;Kolomiets et al 2010).…”