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Scott Watamaniuk, Elena Potapchuk, Stephen Heinen; Pursuing a small spot engages a different mechanism than pursuing a feature on a large object. Journal of Vision 2016;16(12):1352. doi: 10.1167/16.12.1352.
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© 2017 Association for Research in Vision and Ophthalmology.
Our previous work showed that pursuing large objects is less saccadic and less attentive than pursuing a small spot (Heinen et al., 2011; Jin et al., 2014). We proposed that a motion mechanism is predominantly used to pursue large objects while a foveal, position mechanism is engaged to pursue spots. But which mechanism is recruited when observers view small features on a larger pursuit object? To address this question, observers pursued, in separate blocks, either a single spot (0.2 deg) or a spot centered on a larger circular array (6° diameter) of eight 0.2 deg "feature" spots. All stimuli translated across the screen at 7 deg/s. Well after pursuit reached steady state (900-1400 ms), a randomly selected feature spot on the array brightened and enlarged, and observers made a saccade to it and pursued it for the remainder of the trial. In single-spot blocks, the initial spot target disappeared as the saccade target appeared at one of the eight possible feature spot locations. We found an almost complete cessation of catch-up saccades for an extended period preceding the targeting saccade. This saccade quieting period began earlier, and lasted longer, during pursuit of the large object. Saccade cessation was accompanied by a simultaneous reduction in eye velocity. The decrease was greater during spot pursuit, indicating that preparing for a gaze shift hampered pursuit of the spot more than it hampered pursuit of the large object. Therefore, pursuit of a small spot is different from pursuit of a small feature on a large object. These results, combined with our previous work, suggest that engaging a position mechanism to pursue conflicts with preparing a saccade to another target or feature. The brain solves this problem during pursuit of larger objects by relying on the motion system to pursue.
Meeting abstract presented at VSS 2016
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