Wells, Stephen G.; (1999) Factors affecting the storage and reproduction of predictive smooth pursuit eye movements. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The eyes take 100ms to react to a moving visual target. Anticipatory production of internally generated eye velocity can reduce this delay. However, smooth velocities up to only about 5 degree/s can be voluntarily generated without a moving target. In contrast, fast predictive movements without visual feedback occur during anticipatory smooth pursuit (ASP) eye movements. Frequent repetition of brief target ramp movements appears to charge an internal store that is later released as ASP before each ramp.This thesis shows that ASP velocity increases when 1) faster ramps are used (for 12- 50degree /s ramps, the eye typically reaches 60% of target velocity by 100ms after ramp onset), 2) alternate direction rather than unidirectional ramps are used and 3) when audio timing cues are given 600ms before the onset of each ramp. It decreases when a fixation target is present before ramp onset.Several results suggest ASP velocity is not precisely controlled. Variability to consecutive identical stimuli is quite high and some subjects have large directional asymmetries. Furthermore, appropriately scaled ASP velocities cannot be produced when an increase in target velocity is expected.The putative store's longevity was assessed by repetitively presenting brief ramps with different intervals of darkness between each ramp up to 7.2s. Ability to generate fast ASP declined with increasing interval, even with audio timing cues. Similar decreases were not seen in anticipatory tracking movements by the hand.The magnitude of anticipatory eye acceleration before each ramp started and of anticipatory deceleration before each ramp ended was altered by changing the target briefly into an visual acuity target that had to be identified at a set time during each ramp. However, the changes were small suggesting that subjects cannot greatly modify the predictive compromise between optimal tracking of different parts of the target motion waveform.ASP eye movements appear to be a rough estimate of target velocity released with appropriate timing and direction. This rough estimate can significantly improve pursuit whilst awaiting the visual feedback needed for precise pursuit.

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