Abstract
Speech perception is known to rely on both auditory and visual information. However, sound-specific somatosensory input has been shown also to influence speech perceptual processing (Ito et al., 2009). In the present study, we addressed further the relationship between somatosensory information and speech perceptual processing by addressing the hypothesis that the temporal relationship between orofacial movement and sound processing contributes to somatosensory–auditory interaction in speech perception. We examined the changes in event-related potentials (ERPs) in response to multisensory synchronous (simultaneous) and asynchronous (90 ms lag and lead) somatosensory and auditory stimulation compared to individual unisensory auditory and somatosensory stimulation alone. We used a robotic device to apply facial skin somatosensory deformations that were similar in timing and duration to those experienced in speech production. Following synchronous multisensory stimulation the amplitude of the ERP was reliably different from the two unisensory potentials. More importantly, the magnitude of the ERP difference varied as a function of the relative timing of the somatosensory–auditory stimulation. Event-related activity change due to stimulus timing was seen between 160 and 220 ms following somatosensory onset, mostly around the parietal area. The results demonstrate a dynamic modulation of somatosensory–auditory convergence and suggest the contribution of somatosensory information for speech processing process is dependent on the specific temporal order of sensory inputs in speech production.
Highlights
Multiple sensory inputs seamlessly interact in the process of speech perception
We examined the extent to which the perceptual judgments were correlated with event-related potentials (ERPs) amplitude change that were observed in response to changes in the relative timing of somatosensory–auditory stimulation
This study assessed the neural correlate of the temporal interaction between orofacial somatosensory and speech sound processing
Summary
Multiple sensory inputs seamlessly interact in the process of speech perception. Information from a talker comes to a listener by way of the visual and auditory systems. Precise orofacial stretch applied to the facial skin while people listen to words, alters the sounds they hear as long as the stimulation applied to the facial skin is similar to the stimulation that normally accompanies speech production (Ito et al, 2009) Whereas these and other psychophysics experiments have examined somatosensory–auditory interactions during speech processing in behavioral terms (Fowler and Dekle, 1991), neuroimaging studies exploring the relation between multisensory inputs have been limited to AV interaction (van Atteveldt et al, 2007; Pilling, 2009; Vroomen and Stekelenburg, 2010; Liu et al, 2011)
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