Maintaining somatosensory precision in speech

As we talk the nervous system receives both auditory and somatosensory feedback. Accordingly, the motor commands that underlie speech movements may have somatosensory as well as auditory goals. Although audition may appear to be the central player in speech production, somatosensory information plays a role that extends from brainstem responses to cortical control. Here we provide evidence that, independent of the acoustics, somatosensory information is critical to achieving the precision requirements of speech movements. We were able to dissociate auditory and somatosensory feedback by using a robotic device that altered the jaw's motion path, and hence proprioception, without affecting speech acoustics. The loads were designed to target either the consonant or vowel-related portion of an utterance since these are the major sound categories in speech. We found that, even in the absence of any effect on the acoustics, with learning subjects adapted to an equal extent for both kinds of loads suggest ing that somatosensory precision requirements are comparable for both kinds of speech sounds. We provide experimental evidence that the neural control of stiffness or impedance provides for somatosensory precision in speech production.