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

Abstract

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 degrees, 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 degrees 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.

Playing checkers: detection and eye–hand coordination in simulated prosthetic vision

“…In the meantime, however, under the assumption that the image perceived by a retinal prosthesis wearer may indeed be composed of a regular field of fuzzy dots, one can model vision conveyed by such a device through real-time image processing, and present the resulting view to sighted individuals to determine how well they can base decisions on such sparse visual information. Visual object [7] and face [8] identification as well as reading [9][10][11][12] performance using simplified versions of such simulations have been reported previously by researchers in our laboratory and elsewhere; we will refer to this type of visual imagery as pixelized vision.…”

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.…”

Simulation of Artificial Vision, III: Do the Spatial or Temporal Characteristics of Stimulus Pixelization Really Matter?

“…We attempt to mimic the type of visual information provided by a retinal implant, using photodiode technology to transform incident light into an electric signal. With this methodological approach we explored, in a first study, 11 the reading of isolated four-letter words. In central vision, accurate recognition was possible with pixelizations down to 286 pixels, distributed over a 10°ϫ 3.5°viewing window.…”