The Role of Auditory Feedback in Voice Control in Normal and Impaired Hearing

Monitoring of the voice and speech is mediated by the joint operation of forward and feedback connections. Feedforward is responsible for activating learned articulation programs, while feedback provides acoustic and sensorimotor information about the execution of an utterance. Their joint functioning in speech monitoring is described by the DIVA model, which is based on the regulation by nerve centers of auditory information and proprioceptive signals in relation to articulatory programs. Discrepancies between sensory feedback and the representations of acoustic signals in the auditory cortex trigger corrective commands. Auditory feedback in children acquiring speech is necessary for the correct development of articulatory skills, i.e., to form feedforward connections. For this reason, prelingually deafened adults are characterized by significant impairments to articulation due to immature articulatory skills. In postlingual deafness, the previously formed feedforward is preserved, which supports successful pronunciation of phonemes. However, people with sensorineural hearing loss experience deterioration of the monitoring of phonation and articulation through the auditory feedback mechanism, which is expressed as increased voice volume, changes in the spectral characteristics of speech, and instability of the frequency and amplitude of the voice. Similar changes in speech are found in healthy talkers in the presence of noise when it masks the talker’s own voice (the Lombard effect). Speech in noisy conditions is characterized by an increase in voice intensity, a shift in the spectral characteristics of the voice to the high-frequency region, and hyperarticulation. This reorganization of speech is an adaptation of the talker’s voice to background noise and has the purpose of unmasking the voice and restoring auditory feedback.