Abstract
The psychophysics of reading with artificial sight has received increasing attention as visual prostheses are becoming a real possibility to restore useful function to the blind through the coarse, pseudo-pixelized vision they generate. Studies to date have focused on simulating retinal and cortical prostheses; here we extend that work to report on thalamic designs. This study examined the reading performance of normally sighted human subjects using a simulation of three thalamic visual prostheses that varied in phosphene count, to help understand the level of functional ability afforded by thalamic designs in a task of daily living. Reading accuracy, reading speed, and reading acuity of 20 subjects were measured as a function of letter size, using a task based on the MNREAD chart. Results showed that fluid reading was feasible with appropriate combinations of letter size and phosphene count, and performance degraded smoothly as font size was decreased, with an approximate doubling of phosphene count resulting in an increase of 0.2 logMAR in acuity. Results here were consistent with previous results from our laboratory. Results were also consistent with those from the literature, despite using naive subjects who were not trained on the simulator, in contrast to other reports.
Highlights
Images of the text were manipulated in real-time so as to simulate the perception of a thalamic visual prosthesis wearer
COMPARISON WITH PREVIOUS WORK FROM OUR LABORATORY In a previous study we investigated the effect of phosphene count on visual acuity in an isolated letter recognition task with a simulated thalamic visual prosthesis (Bourkiza et al, 2013)
A reduction in eye tracking instrumentation uncertainty to more fully stabilize the phosphene locations on the retina would be highly desirable through, for example, more advanced noise reduction algorithms. This presentation embodies the first quantification of reading performance with a simulated thalamic visual prosthesis, with results demonstrating that reading using a real thalamic device should be of at least comparable performance to reading with a retina prosthesis, with the potential for substantial improvement through training
Summary
Restoring sight to the blind is a challenge that researchers around the globe have been addressing through a variety of approaches, from genetics (e.g., Acland et al, 2001; Beltran et al, 2012), to replacement surgery (e.g., corneal transplant or keratoprosthesis as in Zerbe et al, 2006) to visual prostheses (reviewed in Mertz, 2012; Ong and da Cruz, 2012) such as the device-based approach our laboratory has been investigating (Pezaris and Reid, 2007, 2009; Pezaris and Eskandar, 2009; Bourkiza et al, 2013; Jeffries et al, 2014). An appropriate set of electrodes, the field hypothesizes, could be used essentially as a direct-to-brain display to evoke a more complex visual scene through patterned stimulation, allowing researchers and physicians to bypass the damaged structures and provide restoration of function Among such devices, the thalamic visual prostheses proposed by our group have the potential to restore high resolution vision and be applied to a wide variety of causes of blindness, from retinal disease, to cancer, to trauma (Pezaris and Reid, 2007). Given nearly 100,000 patients with DBS implants worldwide (Tierney et al, 2011), safe and reliable surgical access to the mid-brain for stimulating electrodes is, essentially, a solved problem, overcoming the primary barrier to use of the LGN as a target for artificial vision
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