This research is designed to test the hypothesis that consonant voicing and active lowering of vocal fundamental frequency (F0) are governed by a single phonetic feature-slack vocal folds- by determining if muscles implicated in F0 lowering are also used to achieve voicing. Electromyographic (EMG) studies have established that the infrahyoid strap muscles play an active role in F0 lowering. Contraction of these muscles pulls the larynx downward, causing the cricoid to tilt forward and the vocal folds to slacken. Five studies will be undertaken to test the hypothesis. The first two will compare EMG measurements of strap muscle activity in minimal pairs of voiced and unvoiced consonants, to test for the predicted patterns of increased and suppressed activation. The third study will analyze acoustic signals recorded from individuals before and after having their strap muscles surgically cut (during thyroidectomy operations) to determine if loss of the strap muscles brings about any loss in the ability to voice consonants. The last two studies will control for the possibility that F0 and voicing contrasts have distinct representations in higher level brain function despite being produced with the same articulatory mechanism, using EMG analysis of intonational contours from English and Japanese and their interactions with consonant voicing. This research will improve understanding of laryngeal control and will potentially aid development of voice prostheses for individuals who undergo laryngectomy: An electrolarynx is currently being modeled that can use surface EMG signals from strap muscles as inputs to control both F0 and phonation offset/onset for unvoiced consonants. Understanding of normal strap muscle function in speech can benefit these efforts.
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