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Mehmet Naci Ağaoğlu, Wai (Tiffany) Fung, Susana T L Chung; What does an "artificial scotoma" simulate?. Invest. Ophthalmol. Vis. Sci. 2019;60(9):4379. doi: https://doi.org/.
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Patients with a central scotoma often adopt a retinal location outside the scotoma for seeing, the preferred retinal locus (PRL). Previous studies have reported that the adoption of a non-foveal location for seeing was also observed in people with normal vision when their central vision was blocked by an artificial scotoma. Here, we investigated whether the PRL that develops in response to an artificial scotoma in people with normal vision is the result of visuomotor adaptation, as is the case in patients with a real scotoma.
We used a gaze-contingent paradigm to induce an artificial scotoma that covered the central 8° visual field for 11 subjects with normal vision. Subjects were first implicitly trained to learn to cope with the artificial scotoma by repeatedly searching for a Tumbling E stimulus and identifying its orientation. Subjects’ gaze location and fixation stability were continually monitored throughout training. Following training (~6300 trials), we evaluated subjects’ consistency in using their newly developed PRL, if any, for fixation and making saccades. Six of the 11 subjects were then explicitly trained to use their PRL for making saccades. Training involved making saccades to place the PRL on a small target that was presented at random locations on a display. After ~10000 trials (~64,000 saccades) per subject, subjects were tested again for their consistency in using the PRL in a post-test, where the artificial scotoma was absent in half of the trials.
Following the implicit training task, 10 of the 11 subjects developed a PRL for fixation that was located immediately outside the artificial scotoma, with substantial improvement in fixation stability. Their saccades, however, remained referenced to the fovea, even in the presence of the artificial scotoma. Among the 6 subjects who subsequently underwent explicit training, 4 of them demonstrated the re-referencing of saccades to the PRL after training. However, for trials in which the artificial scotoma was absent during the post-test, all 6 subjects reverted to using their fovea.
The finding that even subjects who had developed a stable saccadic PRL in the presence of an artificial scotoma automatically reverted to using their fovea as soon as the artificial scotoma was removed suggests that the adoption of a PRL in response to an artificial scotoma most likely represents a strategy, instead of a genuine visuomotor adaptation.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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