Collins, Catherine Jane Suzanne; (2000) Intrinsic and extrinsic mechanisms of timing control of visuo-motor activity. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Accurate timing is of fundamental importance in motor control. Its importance in ocular motor control can be readily demonstrated - for example in timing anticipatory smooth pursuit or producing anticipatory saccades. Few studies, however, have specifically examined ocular motor timing mechanisms. This thesis addresses this issue. In the first two studies, established timing paradigms were adapted to make them applicable to ocular motor movements. The Continuation paradigm was used to demonstrate that the Wing and Kristofferson model, which decomposes timing variance into central 'clock' and peripheral 'motor implementation' components, can be applied to saccadic eye movements. The Synchronisation paradigm was also adapted to examine saccadic eye movements and was used to show that response-contingent afferent information is not essential for precise synchronisation of a motor response with an external metronome. In the third study, the development of an anticipatory smooth eye movement response to repeated target motion was enhanced by the presentation, in several different modalities, of regular warning cues which reduced timing uncertainty in the task. This allowed the steady-state level of anticipatory activity to be achieved more quickly than when warning cues were absent. In the fourth study, the timing of head and gaze movements (which are usually very closely coupled) during head-free pursuit was shown to be precisely controlled, even when they were intentionally dissociated. Further, head and gaze movements could be carried out simultaneously at two harmonically-unrelated frequencies with little impairment of timing. These studies have highlighted and quantified the fundamental role of timing in a range of ocular motor tasks. The application of established timing paradigms to a system which differs from other motor control systems in several important respects, has allowed ocular motor timing control to be considered in the wider context of other established motor timing mechanisms.

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