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Jason F Rubinstein, Manish Singh, Eileen Kowler; Effect of priors on smooth pursuit of clear and noisy random dot kinematograms. Journal of Vision 2019;19(10):303b. doi: https://doi.org/10.1167/19.10.303b.
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Smooth pursuit anticipates the direction of future target motion. Once target motion begins, pursuit undergos a transition between dependence on anticipation (priors) and dependence on immediate sensory motion. Principles of optimal cue combination suggest that the relative contribution of sensory motion may be smaller, or take longer to develop, the noisier the motion. Subjects pursued random dot kinematograms (200 dots; 1.6 dots/deg2). Mean direction of dot motion on each trial was chosen from a Gaussian prior with mean=45 deg (up and to the right), SD 10 deg. Direction of motion of individual dots was chosen from a Gaussian likelihood with SD 0 (clear) or 45° (noisy). Dot displacement/frame was larger for the noisy motions to equate stimulus speeds (6 deg/s). Perceptual testing using brief (150 ms) durations confirmed that judgments of motion direction were more variable with the noisier RDKs. Correlations between mean dot direction and pursuit direction increased over time reaching a maximum of ~.75 by 250ms after the start of motion for clear, and .7 by 350 ms for the noisy target motions. The contribution of the immediate sensory motion to pursuit was shown by slopes of the functions relating mean dot direction on each trial to mean pursuit direction for different epochs of time following the onset of target motion. Slopes increased over time reaching asymptotic values near 1 by ~250 ms after motion onset for clear, and ~350 ms for noisy motion. The evolution of slopes over time shows that pursuit assigned greater weight to the current sensory information at a rate that depended on motion noise. These results show that effects of motion priors persist for a longer time after target motion onset when sensory motion is noisier, a result that may be consistent with principles of optimal cue combination.
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