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Alexander C. Schütz, Doris I. Braun, Dirk Kerzel, Karl R. Gegenfurtner; Improved visual sensitivity during smooth pursuit eye movements. Journal of Vision 2008;8(6):218. doi: https://doi.org/10.1167/8.6.218.
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© ARVO (1962-2015); The Authors (2016-present)
Eye movements have various effects on visual perception. During saccadic eye movements, for example, suppression has been reported for visual stimuli being processed in the magnocellular system. Here, we explored the effects of smooth pursuit eye movements on visual sensitivity.
We compared sensitivity for briefly flashed color- and luminance-defined stimuli during pursuit and fixation. Subjects had to track a black target spot that was either stationary (fixation) or moved horizontally (pursuit) with a velocity of 10.57 deg/sec. Contrast sensitivity was measured by means of a blurred 0.3 deg wide horizontal line that appeared for 10 ms 2 deg above or below the pursuit trajectory. The line was defined by an increment or decrement in luminance or in isoluminant red-green color contrast. The results show that contrast sensitivity for luminance stimuli was slightly but significantly reduced during pursuit. However, for color stimuli instead of a decrease, a 15% increase in sensitivity was found during pursuit. The sensitivity enhancement for color was also present for a red pursuit target and a range of speeds (3–15 deg/sec) of the pursuit target.
To test if the increase in sensitivity is specific for a retino-thalamic pathway, we measured sensitivity for high spatial frequency luminance gratings of 14 cpd. Again sensitivity was increased during pursuit compared to fixation. Further we investigated the dynamics of this enhancement by flashing a red horizontal line at different points in time relative to the onset of a step-ramp target. The detection rate rises approximately 50 ms before the onset of pursuit, indicating that the enhancement is triggered by an extra-retinal signal.
These findings indicate an active and selective sensitivity enhancement for the parvocellular pathway during pursuit. A facilitation of the parvocellular system may aim at improving object recognition and increasing sensitivity to small retinal speed errors while tracking objects.
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