Steady state responses to temporally congruent and incongruent auditory and vibrotactile amplitude modulated stimulation

Abstract

Recent research suggests that multisensory integration may occur at an early phase in sensory processing and within cortical regions traditionally though to be exclusively unisensory. Evidence from perceptual and electrophysiological studies indicate that the cross modal temporal correspondence of multisensory stimuli plays a fundamental role in the cortical integration of information across separate sensory modalities. Further, oscillatory neural activity in sensory cortices may provide the principle mechanism whereby sensory information from separate modalities is integrated. In the present study we aimed to extend this prior research by using the steady-state EEG response (SSR) to examine whether variations in the cross-modality temporal correspondence of amplitude modulated auditory and vibrotactile stimulation are apparent in SSR activity to multisensory stimulation. To achieve this we varied the cross-modal congruence of modulation rate for passively and simultaneously presented amplitude modulated auditory and vibrotactile stimuli. In order to maximise the SSR response in both modalities 21 and 40 Hz modulation rates were selected. Consistent with prior SSR studies, the present results showed clear evidence of phase-locking for EEG frequencies corresponding to the modulation rate of auditory and vibrotactile stimulation. As also found previously, the optimal modulation rate for SSR activity differed according to the modality, being greater at 40 Hz for auditory responses and greater at 21 Hz for vibrotactile responses. Despite consistent and reliable changes in SSR activity with manipulations of modulation rate within modality, the present study failed to provide strong evidence of multisensory interactions in SSR activity for temporally congruent, relative to incongruent, cross modal conditions. The results are discussed in terms of the role of attention as a possible factor in reconciling inconsistencies in SSR studies of multisensory integration.

Keywords: Amplitude modulation; Cross-modal correspondence; Multisensory integration; Perceptual sensitivity; Steady-state response; Temporal information.