Optometry and Vision Sciences - Theses
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ItemIntegration of auditory and visual temporal rate in aging( 2017)This thesis investigated how aging affects the integration of visual flicker (the temporal modulation of luminance) with auditory flutter (the temporal modulation of sound amplitude) to produce a unified audiovisual percept of temporal modulation rate. A group of younger and older adults judged the temporal rate of an auditory and/or visual stimulus oscillating at 10 Hz. Whichever sensory modality discriminates temporal rate more precisely, contributes more to the audiovisual percept. Consequently, the first experiment explored how aging affected the precision of auditory temporal rate discrimination relative to vision. Auditory temporal rate discrimination in older adults was degraded by an age-related impairment in sensitivity to auditory amplitude modulation. In subsequent audiovisual experiments, auditory modulation depth was individually tailored to equate flutter and flicker temporal rate discrimination thresholds to normalise for this age-related sensory loss. When auditory and visual rates were conflicting, partial integration distorted perceived rate such that the auditory or visual rate subjectively equivalent to a reference was nonveridical. Distortions in perceived rate were unaffected by older age, indicating that the ability to integrate conflicting auditory and visual rates is preserved in aging. However, younger adults’ heightened sensitivity to auditory amplitude modulation was sufficient to increase the influence of audition on perceived rate when the modulation depth of auditory flutter was the same as the average older adult. Therefore, the age-related impairment in auditory rate discriminability is expected to increase visual influence on audiovisual rate perception in older adults. When auditory and visual rates are identical, temporal rate discrimination thresholds improved in line with statistically optimal integration in younger but not older adults. This indicates an age-related impairment in integration, which will be further compounded by the age-related decline in auditory temporal rate discriminability under natural conditions. These findings indicate that older adults will perceive audiovisual temporal rate differently to younger adults. These age-related changes in audiovisual rate perception will be the complex product of the age-related interaction between rate congruence and integration ability, and the age-related decline in auditory temporal rate discrimination.
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ItemA development of Chinese near logMAR visual acuity charts( 2000)Near visual acuity (VA) test charts using simplified Chinese characters were designed based on the logMAR principle. Two experiments were conducted on native Mandarin-speaking subjects with normal vision. In experiment one, the relative legibility of characters with different strokes (‘complexity’ of from 4 to 10 strokes per character) and the effect of different viewing distances on VA were investigated. No significant difference were found between test distance but significant differences were present between subjects and character complexity. In experiment two, a clinical method of rating VA (VAR) was compared with the determination of a psychometric threshold in 28 subjects, using charts with a 0.05 logMAR step. Results showed that VAR was not significantly different from the 75% psychometric threshold. The assumption made in this thesis that increased stroke density will reduce legibility was confirmed by the experimental results. Two near Chinese logMAR charts were designed with mixed-stroke of characters based on the findings of the first two experiments. In experiment three, a direct comparison of the Chinese near logMAR charts with the established Bailey-Lovie near logMAR chart were performed, using 6 bilingual subjects, a consistent pupil size of artificial pupil, and simulated low vision conditions by defocus. Regression analysis showed a highly correlation between the Bailey-Lovie near logMAR chart and the Chinese near logMAR chart. A correction factor was determined for all Chinese near VA charts that allows for direct comparison to be made with the established Bailey-Lovie near VA charts. A finding of a similar visual acuity from both charts confirmed the Chinese chart as comparable to the current clinical standard.