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The Effects of Aging on Cross-Modal Attention

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abstract
Healthy aging is accompanied by declining sensory function in all five senses and subtle deficits in higher order cognition. Among the age-related changes that have been observed is an increase in multisensory integration. In the young brain, multisensory integration is governed by a combination of stimulus characteristics (spatial location, timing, and intensity) and higher-order cognitive constraints (semantic congruence, attention). Given previous research suggesting that executive functioning and attention might be impaired in healthy aging, it was hypothesized that increased integration resulted from a failure to properly restrict incoming sensory information with crossmodal attention. Behavioral testing comparing reaction times and accuracy during voluntary and involuntary attentional tasks demonstrated that older adults maintained the ability to successfully engage cross-modal attention. Therefore, another behavioral experiment was undertaken to investigate the ability of older adults to restrict multisensory processing using cross-modal attention. The amount of multisensory integration while participants divided their attention across vision and hearing was compared to that when they attended selectively to vision or hearing. Greater multisensory integration was observed with aging in all attentional conditions, suggesting that older adults were processing more to-be-ignored stimuli than younger adults. However, older adults were able to attenuate multisensory integration equivalently to younger adults, supporting the findings from the first study that cross-modal attentional mechanisms are functional in healthy aging. The ix reason for increased integration during selective attention appeared to be that there was an overall increase in the amount of sensory information processed in all conditions. This suggests that the reason for increased multisensory integration with aging is not due to a failure of attention, but rather greater sensory processing at baseline. A functional neuroimaging study was undertaken to investigate the neural mechanisms of a baseline shift in sensory processing. Average quantitative perfusion maps were used to assess functional brain activity in older and younger adults for resting state and visual steady-state conditions. Previous research shows that cross-modal attention acts primarily by suppressing processing of stimuli in the unattended modality. Therefore, relative activity in auditory and visual cortices was examined, as well as the ratio of visual to auditory activity. Results of the imaging experiment supported behavioral observations. Older adults showed relatively greater auditory activity than younger adults at resting baseline. While participants in both age groups showed expected task-related reductions during the visual condition, older adults still exhibited greater activity to background auditory stimuli. Finally, it was hypothesized that the observed baseline increase in processing of unattended auditory stimuli was due to increased activity in the default mode network. Evidence did not support this hypothesis. The default mode was found to have lower resting activity in older adults than younger adults, and default mode activity did not correlate with auditory activity. However, the observation of reduced metabolic activity in the default mode network is novel and important in its own right, as is the suggestion from the data that the default mode network may become decoupled during visual tasks in healthy aging adults.
subject
Aging
Attention
contributor
Hugenschmidt, Christina (author)
Robert C. Coghill (committee chair)
Jeff D. Williamson (committee member)
Mark T. Wallace (committee member)
Joseph A. Maldjian (committee member)
date
2009-04-01T15:33:32Z (accessioned)
2010-06-18T18:57:13Z (accessioned)
2009-04-01T15:33:32Z (available)
2010-06-18T18:57:13Z (available)
2009-04-01T15:33:32Z (issued)
degree
Neuroscience (discipline)
identifier
http://hdl.handle.net/10339/14675 (uri)
language
en_US (iso)
publisher
Wake Forest University
rights
Release the entire work immediately for access worldwide. (accessRights)
title
The Effects of Aging on Cross-Modal Attention
type
Dissertation
Thesis

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