Perceptual objects often comprise of a visual and auditory signature, which arrives simultaneously through distinct sensory channels, and multisensory features are linked by virtue of being attributed to a specific object. The binding of familiar auditory and visual signatures can be referred to as semantic audiovisual (AV) integration because it involves higher level representations of naturalistic multisensory objects. While integration of semantically related multisensory features is behaviorally advantageous, multisensory competition, or situations of sensory dominance of one modality at the expense of another, impairs performance. Multisensory facilitation and competition effects on performance are exacerbated with age. Older adults show a significantly larger performance gain from bimodal presentations compared to unimodal ones. In the present thesis project, magnetoencephalography (MEG) recordings of semantically related bimodal and unimodal stimuli captured the spatiotemporal patterns underlying both multisensory facilitation and competition in young and older adults. We first demonstrate that multisensory processes unfold in multiple stages: first, posterior parietal neurons respond preferentially to bimodal stimuli; secondly, regions in superior temporal and posterior cingulate cortices detect the semantic category of the stimuli; and finally, at later processing stages, orbitofrontal regions process crossmodal conflicts when complex sounds and pictures are semantically incongruent. Older adults, in contrast to young, are more efficient at integrating semantically congruent multisensory information across auditory and visual channels. Moreover, in these multisensory facilitation conditions, increased neural activity in medial fronto-parietal brain regions predicts faster motor performance in response to bimodal stimuli in older compared to younger adults. Finally, by examining the variability of the MEG signal, we also showed that an increase in local entropy with age is also behaviourally adaptive in the older group as it significantly correlates with more stable and more accurate performance in older compared to young adults.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:OTU.1807/29703 |
| Date | 30 August 2011 |
| Creators | Diaconescu, Andreea |
| Contributors | McIntosh, Anthony Randal |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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