This thesis aimed to address two separate issues: 1) the effect of fixation and smooth pursuit eye-movement on motion sensitivity and 2) the effect of age on motion sensitivity. Speed, direction and motion coherence thresholds were measured in older and younger observers during fixation and smooth pursuit. Observers of all ages found it more difficult to discriminate direction during smooth pursuit compared to fixation. An age-related decline in direction discrimination was evident during fixation and smooth pursuit at slow speeds only (Experiment 1). An age-related decrease in retinal luminance failed to explain the decline in direction sensitivity in older observers (Experiment 2). The effect of relative motion was assessed and was found not to influence the threshold difference between eye-movement conditions (Experiment 3). Similar effects of speed and eye-movement condition were found in the trajectory-matching task (Experiment 4). Speed discrimination thresholds were also higher during pursuit compared to fixation (Experiment 5). No age effects were found in either eye-movement condition for speed discrimination. Classification analysis demonstrated that in speed and direction discrimination, old and young observers combined retinal and extra-retinal motion cues to make motion judgements regardless of instructed eye-movement. Overall, the discrimination results support the idea that performance in these tasks is limited by internal noise associated with retinal and extra-retinal motion signals that feed into a combination stage responsible for estimating head-centred motion. Motion coherence thresholds were higher for pursued stimuli compared to fixated stimuli (Experiment 6). In addition, observers of all ages found it more difficult to detect collinear signal motion compared to orthogonal signal motion during pursuit. This pattern was significantly worse in older observers. There was no age-related decline in motion coherence for fixated stimuli. Retinal slip due to inaccurate eye-movements could explain the motion coherence findings.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:585008 |
| Date | January 2010 |
| Creators | O'Connor, Emer |
| Publisher | Cardiff University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://orca.cf.ac.uk/55068/ |
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