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Title: Investigating the effects of ageing on multisensory integration
Author: Couth, Samuel
ISNI:       0000 0004 5356 3149
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2015
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In order to create a holistic percept of our environment, sensory cues occurring from the same event are bound together; a process known as multisensory integration. Previous research suggests that multisensory integration is enhanced as we get older, which might compensate for poorer unisensory functioning, or be due to reduced inhibitory mechanisms to prevent separate sensory cues being combined. As a result, older adults might have less accurate perception of external events and internal body state, which has been linked to fall behaviour. In this thesis, the effects of ageing on multisensory integration were investigated further. In the first experiment, a reaching task was developed to investigate the effect of visual cues on selecting and coordinating an action in younger adults. The action relevance and orientation of a stimulus were found to independently affect different kinematics of the reach, and so can be interpreted as two distinct effects. This same method was then used with an older adult sample, showing that these effects were less dissociated with increasing age. However, older adults also demonstrated more asymmetrical bimanual responses, possibly due to stronger effects of hand dominance with increasing age, thus making it difficult to conclusively disentangle the effects of age on visuomotor processes from the effect of hand dominance. In the experiments which followed, a testing battery was implemented to investigate how ageing affects several aspects of multisensory processing; from the level of sensory detection, through to sensorimotor control of actions. Moreover, this battery included measures of sensory, cognitive and motor functioning, so individual differences in these factors could be taken into account. First, a simple reaction time task demonstrated that for participants who showed significant enhancement, older adults benefitted from combined visual and auditory stimuli more than younger adults. In addition, the fastest unimodal reaction time was related to magnitude of integration, suggesting that only those with the slowest unimodal reaction times benefitted from multisensory stimulation. This has implications for previous studies which have demonstrated a RT benefit for older adults, suggesting that integration might not be as enhanced as these studies describe. Second, a modified version of a well-established task was used to assess the temporal and spatial limits of visual-tactile interactions. Using error rate as the primary measure, both younger and older adults were able to ignore visual distractors when these were temporally discrepant. However, whilst older adults’ tactile judgements were influenced by spatially discrepant visual distractors, younger adults’ were generally much more distracted by irrelevant visual cues. These findings might be related to worse inhibition or a less cautious approach from younger adults. Third, a block size judgement task was used to determine whether younger and older adults rely more on visual or haptic information when presented simultaneously. Older adults were found to rely more on vision than younger adults, who showed more variability between individuals. In the final experiment, hand kinematics were recorded to determine how younger and older adults adapt grasping behaviour according to visual and haptic cues. In contrast to the previous study, older adults adapted their behaviour to the haptic cues more than younger adults. Taken together, these studies suggest that older adults might not integrate visual and haptic information when there is a discrepancy between these cues. Overall, the results of the testing battery suggest that older adults do not show the expected pattern of enhanced integration across tasks. As such, multisensory integration should be considered as a range of separate processes, which might not all be influenced by ageing. The current results are discussed in relation to the high physical and cognitive functioning of the older adults, reduced motivation for the younger adults, or differences in the methods used to assess individual differences to multisensory integration. Each of these points poses a challenge to measuring age-related differences in multisensory integration. Nevertheless, the methods used could have therapeutic implications, especially for older adults who have physically and cognitive senesced to a greater extent.
Supervisor: Not available Sponsor: Frederick Craven Moore Award
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available