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Alexander C. Schütz, Doris I. Braun, Karl R. Gegenfurtner; Contrast sensitivity during smooth pursuit initiation. Journal of Vision 2007;7(9):735. doi: https://doi.org/10.1167/7.9.735.
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Eye movements can change the way we perceive visual stimuli. During saccadic eye movements some stimuli are suppressed and perceptually compressed toward the saccade target [e.g. Ross, Morrone, Goldberg & Burr, Trends in Neurosciences, 2001]. Here we explore whether suppression also occurs during smooth pursuit initiation.
In a 2AFC design we investigated the sensitivity for threshold-level stimuli during the initiation of smooth pursuit eye movements. Subjects had to pursue a step ramp target [Rashbass, Journal of Physiology, 1961] which moved with a velocity of 10.57 deg/s. At any time from 400 ms before target onset to 500 ms after target onset, a blurred 0.3 deg wide horizontal line appeared for 10 ms either 2 deg above or below the pursuit trajectory. The line held the same width as the screen to avoid motion signals during horizontal eye movements. The peak contrast of the line was adjusted to a level just above threshold for each subject. Subjects had to indicate whether the line appeared above or below the pursuit target. Trials with initial saccades during pursuit initiation and trials with low pursuit gain were excluded from the analysis.
The results show distinct changes in contrast sensitivity at different presentation times. However, the pattern of suppression was distinctly different from saccadic suppression. First, the magnitude of suppression was less pronounced during pursuit initiation. Second, suppression was largest at the onset of stimulus motion, rather than at the onset of pursuit. Therefore pursuit suppression is likely to be influenced by other factors than saccadic suppression. Suppression during saccades has to compensate strong retinal motion signals generated by the saccade. The observed pursuit initiation suppression is more likely due to inattentional blindness, since the pursuit target requires the focus of attention during motion onset.
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