A person's ability to see an object clearly is based on both the optical characteristics of their eyes and their ability to keep their eyes oriented toward the target. The ability to accomplish the latter can be compromised by self-motion if adequate compensation for the movement is not provided. The goal of the research presented here is to measure subjects' visual acuity during gaze tasks performed while walking. In addition, the effects of body movements on the gaze goals will be quantified using a measure of head fixation distance (HFD). By defining the distance between the subject and a point in space where minimal ocular compensation would be required, HFD provides a goal-relative measure that captures the integrated contributions from all non-ocular body movements. In Study I, subjects walked on a treadmill at 1.8 m/s and fixed their gaze on visual targets placed in front of them at 0.5 and 4 meters. During the "far" target condition, visual acuity was not different between standing and walking. Shorter HFDs during the "near" condition indicate changes in the coordinative relationships of non-ocular body movements. Although these changes appear to facilitate gaze stabilization by reducing the amplitude of the required eye movements, subjects' acuity was compromised while viewing the "near" target during locomotion. In Study II, treadmill speeds from 1.0 to 1.8 m/s were used to investigate the effects of walking velocity on gaze stabilization of the "near" target. Vertical HFD indicated that head pitch was compensating for more of the vertical trunk translation as walking velocity increased, yet visual acuity became progressively worse. In Study III, the "far" target condition from Study I was repeated to investigate visual acuity and vertical HFD at a sub-step timescale. The vertical HFD was shown to vary within the step-cycle and when compared to an assessment made mid-way between heelstrikes, visual acuity was shown to be compromised immediately following heel contact. The results from these experiments indicate that non-ocular mechanisms contribute to gaze stabilization while walking and provide evidence that ocular control is likely more complex than that provided by simple fixed-gain responses to vestibular stimulation.
| Identifer | oai:union.ndltd.org:UMASS/oai:scholarworks.umass.edu:dissertations-4154 |
| Date | 01 January 2006 |
| Creators | Peters, Brian T |
| Publisher | ScholarWorks@UMass Amherst |
| Source Sets | University of Massachusetts, Amherst |
| Language | English |
| Detected Language | English |
| Type | text |
| Source | Doctoral Dissertations Available from Proquest |
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