Speech Motor Learning in Profoundly Deaf Adults

Speech production, like other sensorimotor behaviors, relies on multiple sensory inputs — audition, proprioceptive inputs from muscle spindles, and cutaneous inputs from mechanoreceptors in the skin and soft tissues of the vocal tract. However, the capacity for intelligible speech by deaf speakers suggests that somatosensory input on its own may contribute to speech motor control and perhaps even to speech learning. We assessed speech motor learning in cochlear implant recipients who were tested with their implants turned off. A robotic device was used to alter somatosensory feedback by displacing the jaw during speech. We found that with training implant subjects progressively adapted to the mechanical perturbation. Moreover, the corrections we observed were for movement deviations that were exceedingly small, on the order of millimetres, indicating that speakers have precise somatosensory expectations. Speech motor learning is significantly dependent on somatosensory input.