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Elizabeth Nawrot, Mark Nawrot, Albert Yonas; Smooth Pursuit Eye Movements and Depth from Motion Parallax in Infancy. Journal of Vision 2010;10(7):471. doi: https://doi.org/10.1167/10.7.471.
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Motion parallax (MP) is a kinetic, monocular cue to depth that relies on both retinal image motion and a pursuit eye movement signal. With MP, depth sign is based on the direction of the smooth pursuit eye movement signal: Retinal motion in the same direction as the pursuit signal is perceived nearer than fixation. Retinal motion in the opposite direction is perceived farther away than fixation (M. Nawrot & Joyce, 2006). In previous research to understand the development of MP in infants we (E. Nawrot, Mayo, & M. Nawrot, 2009) used an infant control habituation procedure with an MP stimulus to determine the average age of dishabituation to a depth-reversed test stimulus. Dishabituation to the change in depth sign is evidence for depth discrimination from MP. Now, our goal is to determine when the developing smooth pursuit system has sufficiently matured in infancy and then directly measure pursuit eye movements in relation to a motion parallax task. We presented 12-20 week-old infants with both a depth-from-MP task and a visual tracking task designed to elicit smooth pursuit (SP). The MP stimulus and procedure is identical to previous research (E. Nawrot, Mayo, & M. Nawrot, 2009). Tracking is elicited with a schematic “happy-face” that translates at 10 deg/sec. Eye movements are recorded using a Tobii systems X120 Eye Tracker. We expect to find that SP gain (eye velocity/target velocity) increases across this age range and pursuit maturity will correlate with the onset of sensitivity to MP. Data collected from 16 infants so far supports the hypothesis that depth from MP requires maturation of SP. In general, younger infants demonstrate more saccadic and lower gain eye movements, without MP, while older infants demonstrate more smooth pursuit tracking of the stimulus and MP.
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