Abstract
BackgroundThere has been plentiful evidence of kinesthetically induced rapid compensation for unanticipated perturbation in speech articulatory movements. However, the role of auditory information in stabilizing articulation has been little studied except for the control of voice fundamental frequency, voice amplitude and vowel formant frequencies. Although the influence of auditory information on the articulatory control process is evident in unintended speech errors caused by delayed auditory feedback, the direct and immediate effect of auditory alteration on the movements of articulators has not been clarified.Methodology/Principal FindingsThis work examined whether temporal changes in the auditory feedback of bilabial plosives immediately affects the subsequent lip movement. We conducted experiments with an auditory feedback alteration system that enabled us to replace or block speech sounds in real time. Participants were asked to produce the syllable /pa/ repeatedly at a constant rate. During the repetition, normal auditory feedback was interrupted, and one of three pre-recorded syllables /pa/, /Φa/, or /pi/, spoken by the same participant, was presented once at a different timing from the anticipated production onset, while no feedback was presented for subsequent repetitions. Comparisons of the labial distance trajectories under altered and normal feedback conditions indicated that the movement quickened during the short period immediately after the alteration onset, when /pa/ was presented 50 ms before the expected timing. Such change was not significant under other feedback conditions we tested.Conclusions/SignificanceThe earlier articulation rapidly induced by the progressive auditory input suggests that a compensatory mechanism helps to maintain a constant speech rate by detecting errors between the internally predicted and actually provided auditory information associated with self movement. The timing- and context-dependent effects of feedback alteration suggest that the sensory error detection works in a temporally asymmetric window where acoustic features of the syllable to be produced may be coded.
Highlights
During the development of speech production, different sorts of sensory feedback help to coordinate the movements of the respiratory, laryngeal, velopharyngeal, and articulatory subsystems
Cutaneous and/or somatosensory information on the status of multiple articulators and auditory information related to produced speech constitute important sources of feedback for speech motor control [1]
Time-asymmetric effect of auditory feedback alteration The experimental results obtained in the current study showed that the ahead-of-time and delayed auditory feedback affected the articulatory lip movement in a time-asymmetric manner during repetitive syllable production
Summary
During the development of speech production, different sorts of sensory feedback help to coordinate the movements of the respiratory, laryngeal, velopharyngeal, and articulatory subsystems. Evidence has been obtained from humans and non-human primates showing that neural activity in the auditory cortex is modulated by selfproduced vocalization [6,7,8,9] In concert with these studies, theoretical models of speech acquisition and production have been proposed, which hypothesize that speech targets represented in auditory space are achieved using an articulatory-to-auditory map trained on self-produced auditory feedback [10,11]. Debate continues as to whether such neural mechanisms help to ensure stability in rapid and complex speech motor control [12,13], aside from the well-studied reflexive adjustment of voice volume or pitch based on auditory information [5,14,15,16,17,18]. The influence of auditory information on the articulatory control process is evident in unintended speech errors caused by delayed auditory feedback, the direct and immediate effect of auditory alteration on the movements of articulators has not been clarified
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