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Title: The adaptive control of saccades in normal and abnormal children and adults
Author: Mezey, Laura Elisabeth
ISNI:       0000 0001 3396 682X
Awarding Body: University of London
Current Institution: University College London (University of London)
Date of Award: 2000
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This thesis examines the metrics of saccadic eye movements and the adaptive gain control of saccades to test the saccadic flight-time minimisation (SFM) hypothesis (Harris 1995, Vision Res. 35(5):691-701). The SFM hypothesis proposes that saccadic gain is determined by the drive to minimise saccadic flight-time and provides an explanation for the well-known undershoot bias of saccades. The level of undershoot in any individual is predicted to depend intimately on both the standard deviation of the error after the primary saccade, and the main sequence for duration for each individual. Experimental data to support both of these predictions of the SFM hypothesis are presented in the first section of this thesis. Children with homonymous hemianopia were found to produce primary saccades with low gains and high standard deviations into their blind hemifield, but not into their seeing hemifield. The retained bias to undershoot, despite the high standard deviation, is proposed to be an adaptive strategy to prevent excessive overshoot and minimise saccadic flight-time when the exact target position is unknown. A similar relationship between the gain and standard deviation of saccades is reported for antisaccades made by normal adults. Between-subject comparisons in a separate experiment revealed a strong correlation between gain over a range of eccentricities and the main sequence for duration to further support the SFM hypothesis. To maintain the gain of saccades at an optimal level the saccadic system is under constant adaptive control. The active functioning of the adaptive control system is demonstrated using an intrasaccadic target displacement paradigm in which the target position is consistently altered during the primary saccade, necessitating a change in saccade amplitude. Gain changes indicate that the goal of the adaptive process is not to minimise average retinal error over time, but is consistent with the SFM hypothesis. The adaptive control paradigm was applied for the first time to children with Dancing Eye Syndrome. These patients are suspected to have defective adaptive control by virtue of proposed neuropathology in the vermis of the cerebellum. All patients but one were able to adaptively adjust the gain of their saccades suggesting no persistent effects of this disorder on the adaptive control system. Explanations are proposed for the single case in which adaptive control was absent. The characteristics of gain in the situations outlined in this thesis support predictions made by the SFM hypothesis. The assumption that minimisation of retinal error is the sole driving force of the adaptive control process is not supported.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Saccadic eye movements; Hemianopia