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P. R. Troyk, N. Srivastava, G. Dagnelie, C. Kufta, D. McCreery, E. Schmid, V. Towle; Human Psychophysical Testing to Access the Feasibility of an Intracortical Visual Prosthesis. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5874. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Despite over three decades of cortical visual prosthesis research, there remains an uncomfortable level of certainty about how well a cortical visual prosthesis might function once implanted in a human volunteer. It is the purpose of this study to improve our estimation of what sensory benefit a particular configuration of an intracortical visual might provide. This estimation will be used as a basis for proceeding with the implantation of a system in a human volunteer.
Using studies from the literature, an estimation was made of the number of intracortical electrodes that could be placed on the dorso-lateral surface of the occiptal lobe. We used this restricted location for our proposed implantation site because our team has accessed that surgical placement of intracortical electrodes along the medial face is not warranted without a stronger need-based motivation. Thus, this represents a conservative approach. A literature survey was performed to determine the likely spatial-field locations of phosphenes that would result from electrode placements on the dorso-lateral surface. An electronic phosphene simulation system, that used eye-tracking virtual reality goggles, was modified to use our estimated cortical phosphene maps. Using the estimated map, the simulated phosphene generation system was used to test the pattern recognition limits of normal subjects presented with groups of simulated phosphenes while performing three spatial recognition tasks.
Our studies showed that placing electrodes on the dorso-lateral surface of the occipital lobe would result in phosphenes that would span up to forty degrees of eccentricity. This is because the electrodes would be placed in V1, V2, and V3. We estimate that the phosphenes would be randomly distributed and of random size. Using our map, in the psychophysical studies, our experimental results show that with as few as 325 phosphenes the above average performance of normal subjects doing pattern recognition tasks was statistically significant.
It appears that an intracortical prosthesis that is limited to the dorso-lateral surface will provide visual functionality that will facilitate a user in performing useful visual tasks, including manual placement of objects and navigation. Presently, we are using these results as a basis for proceeding with a human implantation.
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