Marchant Agustus, JL; (2012) Audiovisual synchrony and temporal-pattern effects on human perception and the human brain. Doctoral thesis , UCL (University College London).

Abstract

This thesis investigates the influence of temporal pattern, both within and between unisensory stimulus trains, on audiovisual interactions in the human brain. Embedded target detection tasks (for intensity oddballs) are used to probe impacts on behaviour while fMRI assesses brain activity. The behavioural experiments in Chapter 2 reveal that temporal predictability of events improves target detection sensitivity, with best performance for isochronous trains. Cross-modal sharing of temporal information is implicated when an accompanying auditory stimulus enhances the impact of timing on visual performance, despite providing no information about which visual stimulus is a target. A follow-up fMRI study in Chapter 3 identifies a related activity pattern in left posterior superior temporal sulcus (pSTS). Chapters 4-7 introduce an additional factor of synchrony between two unisensory stimulus trains, one in audition and one in vision. The experiments in Chapter 4 show that audiovisual synchrony can enhance intensity-oddball target detection in either modality. This effect can interact with the predictability of a complex temporal pattern, and attention to events in both modalities. The fMRI study in Chapter 5 reveals the impact of audiovisual synchrony on behaviour is positively related to activity changes in pSTS. A follow-up fMRI study in Chapter 6 shows synchrony-induced activity enhancement in this region, as well as for sensory-specific cortices and a cortico-striatal network, that depends upon stimuli having a predictable temporal pattern over an extended period. These results indicate that the global temporal pattern of stimuli can modulate event perception and activity in brain regions implicated in early sensory, multisensory and timing processes. The influence of extended temporal predictability during synchronous audiovisual trains and positive correlation with impacts of audiovisual synchrony on target detection supports pSTS as a key cortical multisensory site within a broader network.

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