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I. Obeid, C. Veraart, M.–C. Wanet–Defalque, G. Dekeukelaere, J. Delbeke; Effects of Concurrent Stimuli on Phosphene Characteristics in an Optic Nerve Visual Prosthesis . Invest. Ophthalmol. Vis. Sci. 2005;46(13):1501.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The goal of this work is to enhance our ability to accurately elicit multiple phosphenes in a human volunteer that has been implanted with an optic nerve visual prosthesis. Previously, this volunteer successfully demonstrated the ability to recognize images by integrating series of single phosphenes representing real–time images from a head–mounted camera. Now we seek to enhance this process by including the ability to elicit multiple phospenes simultaneously. Methods: The subject was presented with different sets of three stimuli: two single stimuli, A and B, followed by a paired stimulation, AB. For the paired trials, stimuli A and B were delivered either synchronously, sequentially, or interlaced. The single stimuli were trains of 1–3 biphasic pulses with durations ranging from 21.3–85.2µs, and frequencies ranging from 60–100Hz. Three parameters were measured after each stimulus: the number of distinguishable phosphenes, mean phosphene size, and mean phosphene eccentricity (i.e. distance from the center of the field of view). The specific effects of the multiple stimuli were determined by referencing the parameter values from the AB stimuli to the mean parameter values of the individual A and B stimuli. Results: The data suggest that synchronous stimuli are most likely to produce multiple phosphenes. Furthermore, multiple stimuli tend to produce phosphenes that are closer to the center of the field of view than those of the individual component stimuli. This "centering" phenomenon was seen for synchronous, sequential and interlaced stimuli. Furthermore, it is consistent with earlier work which demonstrated that phosphenes tend to migrate to the center of the field of view as stimulation strength is increased. Based on these results, a model is being built that relates the characteristics of multiple stimuli to those of the resulting phosphenes. Conclusions: This first attempt to understand the perceptual effects of multiple stimulations has shown trends which may be exploited in the future to accurately elicit multiple simultaneous phosphenes in the visual field.
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