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Henry Yuheng Liu, Esther G Gonzalez, Luminita Tarita-Nistor, Efrem Mandelcorn, Martin J Steinbach; Pursuing Perceptual Images in the Absence of Central Vision. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4691.
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© ARVO (1962-2015); The Authors (2016-present)
People can pursue perceptual as well as visible stimuli. We compared the smooth pursuit of patients with AMD and controls in two experiments. In the first, participants pursued the bottom vertex of a moving rhomboid and its amodally completed version covered by an occluder. In the second, participants tracked the imagined center of an invisible rolling wheel when all that they could see were either one (single cycloid) or two (double cycloid) points travelling in a cycloidal path on the rim of the wheel. We hypothesized that patients with AMD would be able to track both the completed and visible pursuit stimuli by using peripheral retinal information.
The eye movements of patients (n = 4) and controls with normal vision (n = 11) were monitored by an infrared eye tracker. In Experiment 1, the rhomboid moved in a predictable sinusoidal path or in a pseudorandom path created by the sum of several non-harmonic sine waves. For all participants we measured retinal slip (root mean square eye position error, or RMSD), mean peak velocity gain, saccade frequency, and saccade amplitude.
AMD patients showed an overall increase in the magnitude of RMS error compared to controls (p = 0.009) with a corresponding reduction in gain (p = 0.006) and more saccades (p = 0.01) with higher amplitudes (p = 0.04) in both experiments. In Experiment 1, controls had significantly larger errors (p = 0.01) and lower gain (p < 0.0001) while tracking the unpredictable than the predictable stimulus path, and more errors (p = 0.001) and reduced gain (p = 0.0003) in the masked than in the unmasked conditions. The patients’ performance, on the other hand, depended on their visual acuity: 1) those with better acuity produced data similar to the controls, and 2) those with worse acuity exhibited better performance with the masked stimulus than with the unmasked stimulus and showed no differences as a function of stimulus predictability. In Experiment 2, controls exhibited better pursuit (i.e., lower RMSD) with the double cycloid than the single cycloid (p < 0.0001) but there was no difference for the patients (p > 0.05) due to poor eye movement control.
Consistent with our hypothesis, AMD patients are able to track a perceptually completed moving stimulus albeit with larger retinal slip and more saccadic eye movements. The pursuit of the cycloids path required a degree of ocular motor control that the patients lack.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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