When formulating an estimate of event time, the human sensory system has been shown to possess a degree of perceptual flexibility. Specifically, the perceived relative timing of auditory and visual stimuli is, to some extent, a product of recent experience. It has been suggested that this form of sensory recalibration may be peculiar to the audiovisual domain. Here we investigate how adaptation to sensory asynchrony influences the perceived temporal order of audiovisual, audiotactile and visuotactile stimulus pairs. Our data show that a brief period of repeated exposure to asynchrony in any of these sensory pairings results in marked changes in subsequent temporal order judgments: the point of perceived simultaneity shifts toward the level of adaptation asynchrony. We find that the size and nature of this shift is very similar in all three pairings and that sensitivity to asynchrony is unaffected by the adaptation process. In light of these findings we suggest that a single supramodal mechanism may be responsible for the observed recalibration of multisensory perceived time.

Lai Yau Ming. / "August 2006." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references (p. 260-290). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese.

PURPOSE: Gait during obstacle negotiation is adapted in visually normal subjects whose vision is temporarily and unilaterally blurred or occluded. This study was conducted to examine whether gait parameters in individuals with long-standing deficient stereopsis are similarly adapted. METHODS: Twelve visually normal subjects and 16 individuals with deficient stereopsis due to amblyopia and/or its associated conditions negotiated floor-based obstacles of different heights (7-22 cm). Trials were conducted during binocular viewing and monocular occlusion. Analyses focused on foot placement before the obstacle and toe clearance over it. RESULTS: Across all viewing conditions, there were significant group-by-obstacle height interactions for toe clearance (P < 0.001), walking velocity (P = 0.003), and penultimate step length (P = 0.022). Toe clearance decreased (approximately 0.7 cm) with increasing obstacle height in visually normal subjects, but it increased (approximately 1.5 cm) with increasing obstacle height in the stereo-deficient group. Walking velocity and penultimate step length decreased with increasing obstacle height in both groups, but the reduction was more pronounced in stereo-deficient individuals. Post hoc analyses indicated group differences in toe clearance and penultimate step length when negotiating the highest obstacle (P < 0.05). CONCLUSIONS: Occlusion of either eye caused significant and similar gait changes in both groups, suggesting that in stereo-deficient individuals, as in visually normal subjects, both eyes contribute usefully to the execution of adaptive gait. Under monocular and binocular viewing, obstacle-crossing performance in stereo-deficient individuals was more cautious when compared with that of visually normal subjects, but this difference became evident only when the subjects were negotiating higher obstacles; suggesting that such individuals may be at greater risk of tripping or falling during everyday locomotion.