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Gayatri P Kaskhedikar, Lindsey Yang, Thomas Boucher, Philip Troyk, Gislin Dagnelie; Development of Mapping Methods with Simulated Phosphenes for Implementation in Intracortical Visual Prosthesis Recipients. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4315. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Cortical visual prostheses evoke phosphenes spatially scattered throughout the visual field in a complex pattern unlike the geometric distribution of the implanted electrode array. Determining consistent and reliable phosphene maps in the prosthesis recipients to effectively convey visual information is crucial. We have devised phosphene mapping methods with simulated phosphenes in sighted individuals based on both absolute estimation of single phosphene locations and relative positions of phosphene pairs.
Three mapping methods were tested in 3 normally sighted individuals. Thirty-two simulated phosphenes or dots were presented in the right hemifield one by one on a display screen while central fixation was monitored by an infrared pupil tracker. The subject's perceived location was recorded on a touchscreen. The subjects’ head position was stabilized and calibration of the pupil tracking and touchscreen systems was conducted. In the first absolute mapping method, dots were sequentially presented and the subject indicated the perceived position on the touchscreen while maintaining central fixation. In the second absolute method, an eye movement made to the remembered eccentric dot location was recorded. Maps from these two tests were super-positioned by two-dimensional translation and scaling. As a relative method to locate and reduce angular distortions, 20 pairs of dots were selected. Each pair was sequentially presented, and the subject traced the relative direction of the two dots on the touchscreen. Three trials were conducted for each test.
The radial distortion from the touchscreen tests in S1 (1.37±0.54) and S2 (1.74±1.12) was higher than those from the eye movement tests (1.17±0.45 and 1.62±0. 70, resp.). In both tests, distortions were lower with higher eccentricity. Angular distortions were substantial, with SD up to 25°. Combining the results from the dot-pair test reduced both radial (1.15±0.27) and angular (0.016°±7.0°) distortions in S1. In S2 and S3 only the angular distortion was relatively reduced while reduction of radial distortions was inconsistent.
The results from these preliminary tests indicate that the combination of the mapping methods can provide phosphene maps with greater accuracy. The optimal integration of information from all 3 tests to obtain reliable phosphene maps is being examined.
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