Abstract
Rapid, accurate reading is possible when isolated, single words from a sentence are sequentially presented at a fixed spatial location. We investigated if reading of words and sentences is possible when single letters are rapidly presented at the fovea under user-controlled or automatically controlled rates. When tested with complete sentences, trained participants achieved reading rates of over 60 wpm and accuracies of over 90% with the single letter reading (SLR) method and naive participants achieved average reading rates over 30 wpm with greater than 90% accuracy. Accuracy declined as individual letters were presented for shorter periods of time, even when the overall reading rate was maintained by increasing the duration of spaces between words. Words in the lexicon that occur more frequently were identified with higher accuracy and more quickly, demonstrating that trained participants have lexical access. In combination, our data strongly suggest that comprehension is possible and that SLR is a practicable form of reading under conditions in which normal scanning of text is not possible, or for scenarios with limited spatial and temporal resolution such as patients with low vision or prostheses.
Highlights
These prosthetic reading methods require scanning small patches of text by moving the video camera. While this is similar to the eye movements that occur during normal reading, continual movements present three primary hurdles for reading with a visual prosthesis, associated with contrast polarity, spatial resolution, and temporal resolution
We tested the ability of normally sighted participants to read words, sentences, and paragraphs presented as a sequential stream of single letters
Reading rates and accuracies were similar under reading conditions in which the rate of letter presentation was fixed or controlled by the participant
Summary
Over a dozen teams are developing visual prostheses, which aim to return some visual sensitivity to blind people by electrically stimulating the retina (Argus II Retinal Prosthesis System, Second Sight Medical Products Inc “Argus II”; Dowling, 2009; Zrenner et al, 2011), lateral geniculate nucleus in the thalamus (Pezaris and Reid, 2007; Pezaris and Eskandar, 2009), or primary visual cortex (Brindley and Lewin, 1968; Dobelle and Mladejovsky, 1974; Dobelle et al, 1974; Schmidt et al, 1996; Bradley et al, 2005; Tehovnik and Slocum, 2007). All previous approaches to simulating prosthetic reading have required converting a high resolution video signal into a continually changing, but low spatial resolution pattern of electrical stimulation, where each pixel in the simulated image will correspond to an electrically generated phosphene (Cha et al, 1992; Sommerhalder et al, 2003, 2004; Dagnelie et al, 2006; Fu et al, 2006). These prosthetic reading methods require scanning small patches of text by moving the video camera (i.e., with the head or eyes). While this is similar to the eye movements that occur during normal reading, continual movements present three primary hurdles for reading with a visual prosthesis, associated with contrast polarity, spatial resolution, and temporal resolution
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