Recalibration of auditory perception of speech due to orofacial somatosensory inputs during speech motor adaptation.

Speech motor control and learning rely on both somatosensory and auditory inputs. Somatosensory inputs associated with speech production can also affect the process of auditory perception of speech, and the somatosensory-auditory interaction may play a fundamental role in auditory perception of speech. In this report, we show that the somatosensory system contributes to perceptual recalibration, separate from its role in motor function. Subjects participated in speech motor adaptation to altered auditory feedback. Auditory perception of speech was assessed in phonemic identification tests before and after speech adaptation. To investigate a role of the somatosensory system in motor adaptation and subsequent perceptual change, we applied orofacial skin stretch in either a backward or forward direction during the auditory feedback alteration as a somatosensory modulation. We found that the somatosensory modulation did not affect the amount of adaptation at the end of training, although it changed the rate of adaptation. However, the perception following speech adaptation was altered depending on the direction of the somatosensory modulation. Somatosensory inflow rather than motor outflow thus drives changes to auditory perception of speech following speech adaptation, suggesting that somatosensory inputs play an important role in tuning of perceptual system.