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Gloria Sun, Steven L. Prime; Trans-saccadic Motion Tracking in a Time-to-Contact Task. Journal of Vision 2019;19(10):238c. doi: https://doi.org/10.1167/19.10.238c.
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Transsaccadic perception describes our perceived visual stability despite images shifting across the retina due to saccadic eye movements. Visual stability is thought to be maintained across saccades due to spatial updating mechanisms that track object locations over the saccade. However, transsaccadic research has focused on static objects; few studies have examined how we track moving objects during a saccade. Niemeier, Crawford, and Tweed (2003) found that intrasaccadic spatial displacements of visual stimuli are easier to detect when saccades are perpendicular to the direction of the displacement, compared to saccades parallel to displacement. Here, we examined whether similar effects of saccade direction influence transsaccadic motion tracking in a predicted-motion time-to-contact (TTC) task. Subjects maintained fixation on a cross while tracking a moving dot which translated across the screen towards a line. During movement, the dot would become occluded behind a grey bar. Subjects then estimated when the occluded dot had reached the line via a button press. During the fixation task, participants maintained fixation on a stationary fixation cross. In the saccade task, the cross moved to a new location when the dot disappeared behind the occluder, prompting a saccade. Saccades were either parallel or orthogonal to dot motion. Dot motion (right or left) and line location on occlude (near, middle, or far) were also varied. Eye position was monitored using a SMI RED-m eyetracker. Results showed that the effect for line location was only significant in the saccade task, and that error increased with increased line distance, suggesting that saccades introduce error in TTC estimations. In the fixation task, TTC estimations were most accurate when subjects fixated on the same side of the screen from which the dot originated. These novel findings provide insight into people’s accuracy in predicting the future location of objects across saccades.
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