154th ASA Meeting, New Orleans, Louisiana

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Somatosensory Adaptation in Deaf Adults

Sazzad Nasir, nasir@motion.psych.mcgill.ca
McGill University,
Montreal, Canada

David J. Ostry
Haskins Laboratories,
New Haven, CT

Popular Version of Paper 4aSC7, “Speech motor learning without hearing.”
Presented 10:55a.m. Friday Morning, November 28, 2007,
154th ASA Meeting, New Orleans, LA.

As we speak, we receive sensory inputs from multiple modalities such as auditory feedback from our own voices and somatosensory information from the tissues and muscles of the vocal tract. We know relatively little about the role of somatosensory inputs in speech motor control. However, the ongoing availability of somatosensory information may well help explain a longstanding puzzle in speech production, that is, how post-lingually deaf adults, in the absence of any substantial hearing, maintain reasonably intelligible speech for many years following hearing loss.

In this study we have assessed the role of somatosensory feedback in speech production in subjects with cochlear implants who were tested with their implants turned off. We tested them in this manner in order to make sure that the only sensory information they received as they spoke was based upon somatosensory inputs. We reasoned that if somatosensory input was important in speech production, these deaf speakers might correct for changes to that sensory input alone. We introduced these changes using a robotic device that very slightly altered the motion path of the jaw during speaking and hence somatosensory feedback. We found that with training our subjects corrected for the small perturbation that the robot applied, such that the motion path returned to that usually experienced under normal conditions. Thus even in the absence of auditory feedback, somatosensory input guides speech movements in post-lingually deaf subjects. In this study all five of our subjects with cochlear implants showed varying degrees of adaptation to these loads compared to only four out of six subjects in an age matched control group. This may indicate that there is an even more prominent, but a hitherto unappreciated, role for somatosensory feedback in people with hearing loss.

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