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Matteo Lisi, Patrick Cavanagh; Cooperative interactions between saccadic and pursuit planning when targeting a moving object. Journal of Vision 2017;17(10):1278. doi: 10.1167/17.10.1278.
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When an object of interest moves we use a combination of smooth pursuit and saccadic eye movement to stabilize its image on our retinae and keep it within the region of high visual acuity near the fovea. In this study we investigated the cooperative interactions between saccadic and pursuit eye movements. We asked human observers to intercept and track with their gaze a target moving around a circular trajectory centered on the initial fixation. In our paradigm the eccentricity of the target does not increase as it moves, hence the accuracy by which the first catch-up saccade compensates its velocity is not confounded by the typical saccadic amplitude undershoot (Becker & Fuchs, 1969). Saccade directions revealed, on average, a perfect compensation of target velocity, even when multiple target speeds were interleaved within the same block, and in many cases the saccade landed ahead of the target, anticipating its upcoming displacement. After the first saccade, the speed of the pursuit in the open-loop interval (from 20 to 80ms after saccade landing) was negatively correlated, both on a trial-by-trial basis and across observers, with the saccade direction error: the more the saccade was directed ahead of the target, the slower the speed of the pursuit. Since online visual information cannot modulate pursuit speed during initiation (Lisberger, 2010), this modulation of post-saccadic pursuit must originate from information gathered before the saccade. Taken together these findings indicate that 1) interceptive saccades are guided by a prediction about where the target will be at the time of saccade completion, and 2) the pursuit system uses the error between this extrapolated position and the expected saccade landing to optimize the initial open-loop pursuit after the saccade.
Meeting abstract presented at VSS 2017
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