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Bosco S. Tjan, MiYoung Kwon, Anirvan S. Nandy; Changes in oculomotor behavior induced by a simulated central scotoma. Journal of Vision 2011;11(11):484. doi: 10.1167/11.11.484.
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The visual system often adopts one or more preferred retinal loci (PRL) for fixation in response to central field loss caused by real or artificial scotoma. White and Bedell (1990) found that one-third of their subjects with central field loss demonstrated complete oculomotor re-referencing, shifting the oculomotor reference from the fovea to a non-foveal PRL. Whether a PRL induced by artificial scotoma can lead to a similar shift of the oculomotor reference remains unclear.
We used a gaze-contingent display to simulate a 10-degree central scotoma. Normally-sighted subjects performed a demanding visual-search task for up to 15 hours (spread over weeks) without being instructed on how to use their peripheral vision. The task contained two components: 1) target-object tracking, requiring subjects to track the search target as it was randomly displaced against a uniform background; 2) visual search, requiring subjects to detect the search target amidst clutter. Oculomotor performance was measured during the object-tracking component.
We observed a fast establishment of PRL (within 3 hours of testing) in all four subjects. Three subjects spontaneously formed a single PRL for fixation near the border of the scotoma, while the fourth developed two PRLs. For the single-PRL subjects, median saccade-latency continued to decrease throughout the experiment (below 300 ms after 7 hours). For these three subjects, their first saccade landing position after each target movement was near their fixational PRL and distant from the fovea, demonstrating oculomotor re-referencing. The variance of the first-landing site dropped below 0.5 degree within 8 hours. The same PRL was retained for at least one week after the experiment.
Our results suggest that PRL induced by an artificial central-scotoma generally leads oculomotor re-referencing within a relatively short period of time. The artificial scotoma is viable for modeling the oculomotor behavior of patients with central scotoma.
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