Ocular limit cycles induced by delayed retinal feedback

Abstract

Lisberger's and Robinson's models of smooth pursuit predict very different results from altering retinal feedback delay. We have therefore investigated the effects of increasing the retinal feedback time delay in three normal human subjects by means of an artificial feedback paradigm. When additional delays were incorporated into the retinal feedback path a threshold was reached beyond which the eye exhibited sustained self-excited oscillations or "limit cycles". The oscillation period increased linearly (as the added delay was increased) with slopes ranging from 1.41 to 1.6 with zero-delay intercepts of between 212 and 306 ms. Contrary to our experimental findings the Robinson and Lisberger models predict that the plot of oscillation period against added delay should have a slope of 3.4 and 2.7 and an intercept of 479 and 554 ms, respectively. Neither model produced comparable limit cycles, both being unstable at delays greater than 280 ms. Our results imply that the models of smooth pursuit need to incorporate predictive control.

Interlimb differences of directional biases for stroke production

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Evidence for Object Permanence in the Smooth-Pursuit Eye Movements of Monkeys

“…Perhaps most importantly, models of the pursuit kernel allow us to understand when behavior is expected given the retinal motion and when additional factors such as descending modulation, predictive mechanisms, or visual illusions must be postulated (Pola and Wyatt 1997;Wolpert et al 1993). In the present study, the near-normal pursuit maintenance observed during target occlusion could easily have been attributed to a memory or expectation of target velocity.…”

Acquired Nystagmus

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