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Clara Bourrelly, Julie Quinet, Laurent Goffart; Unsupervised dynamic morphing of a spatiotemporal visual event during its oculomotor tracking. Journal of Vision 2014;14(10):492. doi: 10.1167/14.10.492.
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A target moving in the visual field triggers an interceptive saccade that brings the target image onto the fovea. This foveation is maintained more or less efficiently by two types of tracking eye movements: low-velocity movements (pursuit) and catch-up saccades. Fleuriet & Goffart (2012) hypothesized that the oculomotor system is driven by an estimate of the expected current target location. We suggest that this ability to continuously encode, in spite of neural delays, the "here-and-now" position of a moving target, requires memorization of the trajectory. We further developed this hypothesis by studying how three inexperienced monkeys tracked a small moving target. Their eye movements were recorded with the search coil technique. Each trial started with foveation of a central target which, after a variable interval, stepped 16 deg upward/downward along the vertical meridian, then immediately moved horizontally and smoothly for 16 deg with a constant, accelerating or decelerating velocity, and disappeared. The monkey was rewarded if its gaze tracked the target within a relaxed fixation window (8 deg radius). We analyzed the evolution of eye movements over several consecutive days. Initially, the tracking was mostly composed of saccades separated by periods during which gaze slowly moved toward the target. Exception made of saccades, the gaze lagged behind the target. The pursuit gain increased with the number of trials and training days. The increase in pursuit velocity was associated with a reduction in the number and amplitude of catch-up saccades and gaze sometimes moved as if it were locked onto the target. Our work shows that the ability to continuously maintain the image of a moving target onto the fovea evolves over time. With practice, foveal signals dominate the visuomotor channels and the tracking transitions to a mode that mimics the target dynamics.
Meeting abstract presented at VSS 2014
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