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Dilce Tanrıverdi, Didem Alashan, Mustafa Alperen Ekinci, Inci Ayhan; The Effect of Target Motion and Smooth Pursuit Eye Movement on the Visibility of Isoluminant Target Gratings. Journal of Vision 2021;21(9):2619. doi: https://doi.org/10.1167/jov.21.9.2619.
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Contrast sensitivity to brief flickering chromatic stimuli is higher during pursuit than during fixation (A. C. Schütz, D. I. Braun, D. Kerzel, K. R. Gegenfurtner, 2008). Here, in the first experiment, we tested this using drifting stimuli and measured the detection thresholds as a function of the congruency between the directions of eye movement and grating motion. In different conditions, the target (a magenta-cyan isoluminant sinusoidal grating, 1 cpd, drifting at a speed of 4 deg/sec) was presented inside a rectangular window with 1deg eccentricity to the static fixation spot or moved horizontally (9 deg/sec) across the screen together with the fixation. In a 2-AFC task, subjects reported whether the target appeared above or below the fixation. Similar to Schütz et al, visual sensitivity to dynamic isoluminant gratings was enhanced in the presence of pursuit. Furthermore, thresholds during pursuit were 25% lower than those during fixation when eyes and sinusoidal grating moved incongruently, as opposed to when they moved congruently (15% drop from the baseline). In a second experiment, we investigated the presence of an inducer stimulus on the target visibility. Visibility of dynamic sinusoidal target patterns leading the inducer, containing phase-congruent motion are high, indicating a reduction in discrimination thresholds compared to those in phase-incongruent-motion condition (N. W. Roach, P. V. McGraw, A. Johnston, 2011). Roach et al studied predictive mechanisms with achromatic gratings while eyes were steady. Here, we aimed to investigate this phenomenon using isoluminant gratings and in the presence of pursuit eye movements. We found that the phase modulation demonstrated for the leading targets is absent at isoluminance. Furthermore, thresholds are lower for the trailing targets compared to the leading targets in the presence of pursuit. These findings suggest separate mechanisms for the effects of eye movement and inducer motion on the visibility of isoluminant stimuli.
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