The Effect of Ageing on Visuo-tactile Processes

Abstract

Multisensory processing unifies a variety of sensory information to structure both the environmental and body perceptions. This holds especially for the near-space (peripersonal space) visuo-tactile processing as it anchors both types of perception to enable motor- related behaviours. However, visuo-tactile processing and the associated behaviours are likely to be impacted given the known biological changes experienced by older adults. This thesis attempted to understand any age effect over the visuo-tactile peripersonal space, predominantly the spatial aspect, via three behavioural experiments (young, n = 25; old, n = 25). In Experiment 1 (young mean age = 25.89 ± 3.11) (old = 71.42 ± 7.64), the cross-modal congruency task added a visual distractor at the mid-height eye-level of the opposite hemispace, relative to the tactile target during selective attention (i.e. ignore the distractor while focusing on the target). In turn, any age effect over the visuo-tactile spatial discrepancies, and thus the spatial limit to which multisensory integration occurs was further assessed. In Experiment 2 (young = 23.37 ± 7.46) (old = 68.28 ± 3.83), the temporal order judgment task verified whether temporal acuity modulation was subjected to visuo-tactile spatial discrepancy manipulation during stimuli divided attention. If validated, the acuity then indexed the age effect over the visuo-tactile spatial limit during stimuli divided attention. In Experiment 3 (young = 25.52 ± 6.36) (old = 71.60 ± 4.55), the rubber hand illusion assessed the effect of age on the visuo-tactile spatial limit of displacing a body ownership onto a rubber hand. In addition, the age effect to which the rubber hand ownership occurs during visuo-tactile temporal manipulation was also targeted. In Experiment 1, contrasting to younger adults, older adults did not exhibit any significant visuo-tactile interaction regardless the distractor sites, thus the effect of age over the visuo-tactile spatial limit during selective attention was not drawn. In Experiment 2, the acuity did not significantly differ during visuo-tactile spatial discrepancy manipulation, suggesting the acuity is unable to index the visuo-tactile spatial limit, nor any age-related difference during divided attention. In Experiment 3, a null age effect was reported over the visuo-tactile spatial limit of enabling a significant rubber hand ownership. However, a significantly greater and weaker ownership was observed during visuo-tactile temporal synchrony and asynchrony respectively for older than younger adults. Overall, the absence of age effects from Experiment 1 and 2 should not be overstated since the effects are likely to be masked by an external variable(s). In Experiment 1, the variables discussed are in relation to the higher cognitive demand and the lower visual acuity found amongst older adults. In Experiment 2, the addition of an estimation phase, unimanual nature and the increased visuospatial certainty of the experiment were discussed. Otherwise, Experiment 3 supports an age-dependent during temporal, but not the spatial aspect of the visuo-tactile space when anchoring a body ownership. Regardless, these experiments demonstrated the difficulty of extracting age-related differences in multisensory integration. However, amongst the earliest in the literature, age effects and a null age effect over the temporal and the spatial aspects of the rubber hand illusion respectively were observed.

Date of Award	1 Aug 2018
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Ellen Poliakoff (Supervisor) & Rebecca Champion (Supervisor)