Speech sensorimotor adaptation using altered auditory feedback in cochlear implant users
Résumé
Precise speech production depends on fine motor control that minimizes errors in the produced sound. However, this control process can be disrupted when sensory signals are degraded, such as in auditory deprivation. For deaf individuals, cochlear implants (CIs) are the most effective intervention. Although CI users can acquire speech abilities approaching those of normal-hearing individuals, earlier implantation is associated with better outcomes in both speech production and perception. It is therefore important to investigate how CI profiles influence the development of speech sensorimotor function. In the present study, we applied a laboratory-based sensorimotor adaptation paradigm using altered auditory feedback (AAF), and examined whether CI users with early implantation and long-term experience exhibit speech motor adaptation. Their responses were compared with those of deaf individuals with different CI profiles, normal-hearing controls, and normal-hearing participants tested with a CI simulator. Participants includes seven young adult native French speakers (18–35 years) who were long-term CI users (>10 years; ). For comparison, we also tested seven deaf individuals outside the target CI profile, including short-term CI users (HI-2), seven normal-hearing controls (NH-1), and seven normal-hearing participants tested with a CI simulator (NH-2). The same AAF procedure was applied across all four groups. Participants repeatedly produced the vowel /ø/ embedded in the French word deux (“two” in English). During the task, the second formant (F2) of the vowel was gradually increased to shift the sound toward /e/. This perturbation was applied over 50 trials with a gradual increase, followed by an additional 50 trials during which the maximum alteration was maintained. Only in the NH-2 group was a CI simulator used, consisting of sine-vocoded speech with six frequency bands. Speech adaptation was quantified by comparing the F2 amplitude at the end of the training phase with baseline production measured before training. We found that the HI-1 group showed clear adaptation in response to altered auditory feedback. The adaptation amplitude was comparable to that observed in the NH-1 group, indicating that cochlear implants effectively supported the detection of precise auditory errors required for sensorimotor adaptation. In contrast, adaptation was limited in the HI-2 group. A similar limitation was observed in the NH-2 group, suggesting that degraded auditory feedback restricts the effective use of auditory error signals. These results demonstrate that deaf individuals can adapt to auditory errors when such errors are reliably detected through CIs. Although CIs are effective, efficient use of auditory feedback for precise sensorimotor control may depend on implantation at an appropriate developmental stage and long-term auditory experience.
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