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Mehmet Agaoglu, Christy Sheehy, Pavan Tiruveedhula, Austin Roorda, Susana Chung; Enhancing discrimination of fine spatial details with fixational eye movements: Is there an extra-retinal component?. Journal of Vision 2017;17(10):1157. doi: https://doi.org/10.1167/17.10.1157.
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Fixational eye movements (FEMs) have been known to prevent visual fading. Recent work showed that when FEMs are compensated for by stabilizing visual stimuli on the retina, orientation discrimination of high-spatial frequency gratings is significantly impaired. Here, we tested the hypothesis that FEMs are optimally tuned for discrimination of fine spatial details at the fovea. We asked five observers to report the orientation (±45°) of a 12cpd grating. We used a state-of-the-art Tracking Scanning Laser Ophthalmoscope to deliver the stimuli. By using a range of stabilization gains, i.e., how much of FEMs is compensated for, we obtained a wide range of retinal motion across trials. Note that in contrast to the trials where stimulus position was modulated (gain≠0), there was no stimulus motion on the display in the unstabilized trials (gain=0). We extracted eye and stimulus positions from recorded videos using a cross-correlation method, and sorted trials based on the area enclosed by the 68% isoline (ISOA) of the distribution of retinal positions of the grating. Consistent with previous reports, we found that performance in the unstabilized trials was significantly higher than the minimum performance in the stimulus-modulated trials with smaller ISOAs (less retinal motion) [84±2% vs 75±2% correct]. However, contrary to the optimal tuning hypothesis, performance in the stimulus-modulated trials increased, and for some observers, showed non-monotonic changes with decreasing ISOAs. The comparison of performance at the smallest ISOAs and the unstabilized performance yielded no significant difference. Rather surprisingly, performance in a set of stimulus-modulated trials with comparable retinal motion (mean ISOA) as the unstabilized trials [74±3%] was significantly lower than the unstabilized performance, suggesting that retinal motion due to FEMs is not the sole reason of performance enhancement. When retinal motion and eye movements are fully matched, performance deteriorates suggesting involvement of an extra-retinal process.
Meeting abstract presented at VSS 2017
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