Extending the temporal principle of multisensory integration: a psychophysical and EEG investigation of cross-modal acoustic and vibrotactile amplitude modulation

The major aim of the current thesis was to examine whether the temporal principle of multisensory integration could be extended to include the cross-modal temporal congruence of other stimulus features. According to the temporal principle, cross-modal synchrony between the onsets of multisensory stimuli is fundamental to the binding of multisensory information, or multisensory integration. The examination of other temporal features in multisensory contexts remains limited. Amplitude modulation (AM) has an analogous influence on auditory and vibrotactile sensory processing and perception. This cross-modal dependence of the auditory and tactile modalities on temporal processing potentially facilitates multisensory integration. However, the role of this temporal feature in auditory and vibrotactile multisensory integration remains unexplored. Psychophysical studies show that both auditory and vibrotactile sensitivity varies as a function of AM rate. Electroencephalography (EEG) research shows that the steady-state response (SSR), a sensitive measure of entrained oscillatory mechanisms, is also sensitive to AM rate. It has been proposed that the SSR reflects oscillatory activity with a functional role in the perceptual analysis of the temporal features of sensory stimulation. Subsequently, the SSR may be a potentially important EEG measure for multisensory integration, as recent theories propose that entrained oscillatory activity provides a flexible and dynamic mechanism for multisensory integration. It currently remains unknown as to whether the entrained oscillatory activity underlying the SSR also plays a vital role in auditory and tactile multisensory integration. Across four separate studies, the current thesis investigates how the cross-modal temporal congruence between auditory and vibrotactile stimuli influences perceptual sensitivity, SSR activity and the potential relationship between them. Taken together, findings from the current thesis propose that the cross-modal temporal congruence of temporal features, beyond stimulus onset synchrony, can dramatically influence perceptual sensitivity and the SSR. However, little evidence was found to suggest that the temporal principle extends to acoustic and vibrotactile amplitude modulation congruence.