<p>Audio-visual temporal processing, and integration of auditory and visual information, is necessary for perceiving the world around us. Although previous research has indicated a slowing of temporal processing in older adults for unisensory stimuli, little work has examined the role of aging on multisensory temporal processing. The goal of this thesis is to use temporal-order judgment (TOJ) tasks to investigate age-related changes in audio-visual temporal processing. Overall, our results indicate that older adults do not demonstrate impairments on simple audio-visual TOJs, but they do exhibit deficits on more complex TOJ tasks. We also found no influence of spatial cues on TOJs for younger or older adults. Finally, we found age differences in complex TOJ tasks could not be explained by changes in the ability of older adults to detect a gap between sequential visual stimuli. The work in the thesis suggests that although there may be slowing in audio-visual temporal processing in complex situations, there are circumstances where audio-visual temporal processing is spared. By categorizing multisensory processing deficits in the elderly, we can aim to improve quality of life by preventing fails and perpetuating social interactions.</p> / Master of Science (MSc)

<p>Multiple reference frames are used to interact with our surroundings. When these reference frames are in conflict, processing errors can occur. For tactile stimuli, this conflict is highlighted when the hands are crossed over the midline of the body. In this posture, vibrotactile temporal order judgments (TOJs) presented to the hands are impaired compared to an uncrossed posture. This decrease in temporal processing is known as the crossed-hands deficit. The deficit was explored in depth throughout this thesis. In Chapters 2, 3 and 4 different elements of the crossed-hands deficit were evaluated including its connections to the rod and frame test, individual and sex differences within the TOJ task, as well as the influence of vision and body position. These elements were framed with underlying goal of investigating the root cause of the deficit. The data presented here provided evidence for a conflict model of crossed hands processing. A conflict between the internal and external reference frames produced the deficit in temporal processing when the hands were crossed. The role of the body’s midline in understanding multisensory integration was further considered in Chapter 5 through the rubber hand illusion, which is a visuotactile phenomenon whereby an unseen real hand is mislocalized towards a seen rubber hand. When the real hand, rubber hand, or both were crossed over the midline the illusion did not occur. It was hypothesized that a failure to integrate the tactile information presented to the real hand with the visual rubber hand was responsible for the absence of the illusion. Taken together, the data presented in this thesis contribute to the greater understanding of how reference frame conflicts are resolved, particularly when the conflict occurs across the body’s midline.</p> / Doctor of Philosophy (PhD)