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Liancheng Yang, Haichun Sun, William Diaz, Krishna Sargur, Gislin Dagnelie; Phosphene Mapping to fine-tune local clusters using a paired dots test. Invest. Ophthalmol. Vis. Sci. 2022;63(7):4521 – F0308.
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© ARVO (1962-2015); The Authors (2016-present)
The Intracortical Visual Prosthesis (ICVP) project will implant many (160 – 400) electrodes into a patient’s cortex. An accurate phosphene map is needed to present images to ICVP wearers with minimal distortion. As some phosphenes may form closely spaced clusters, this problem becomes significant with absolute mapping methods. Therefore, we created a relative mapping technique presenting pairs of dots for clustered phosphenes.
Combining the VIVE Pro Eye headset (eye and head tracking) and a Polhemus G4 finger tracker in Unity gaming platform, we tested sighted subjects facing a 36” radius concave sphere cap.We created a set of 16 randomized dots in the lower left quadrant, representing phosphenes from electrodes in the upper right visual cortex . To limit the number of pairs (which for 160 electrodes would be 12720), we only tested pairs within clusters: Only pairs for which the relative proximity (rp; i.e., pair separation / pair eccentricity) was less than a cut-off value were selected; at rp ≤ 25%, we get 11 pairs (chart 1).During testing, subjects used the left index finger to indicate the direction between dots in a pair shown in the headset. Subjects performed a practice trial (5 pairs), followed by 3 tests (11 pairs each).
With data sets collected from 23 subjects, we calculate the direction distributions for each pair; as the distance of the dot pair increased, the SD of the distribution decreased, indicating that subjects were able to indicate the direction more precisely. The same relationship was found for relative proximity (box plot size in chart 2). With 5 subjects who were tested twice, we found that subjects improved both accuracy and precision of the direction settings.
The small deviation angles demonstrate that relative direction mapping provides a reliable basis for rearranging phosphenes within local clusters. Limiting pairs to dots within clusters keeps the total number of pairs to be presented to a manageable number compared to the complete combinatorial pairs required for a complete relative mapping. Combined with the absolute mapping techniques we are developing this will allow robust phosphene map construction within a reasonable time frame.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.
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