Observation of laryngeal control for voicing and pitch change by magnetic resonance imaging technique

Phonatory control by laryngeal movement is discussed by summarizing our two previous studies regarding the role of vertical larynx movement based on magnetic resonance imaging (MRI) observation. The first study focuses on a fundamental frequency (F0) control mechanism involving vertical larynx movement. Mid-sagittal images were recorded during vowel productions with a descending musical scale. Successive display of the images demonstrated larynx lowering along forward convexity of the cervical spine. This movement produces a rotation of the cricoid cartilage to shorten the vocal folds because the posterior plate of this cartilage moves almost parallel to the spinal convexity. This F0 lowering mechanism by larynx lowering provides a possible physiological account for the phenomenon that low tones tend to be associated with low larynx positions. The second study deals with a voicing control mechanism for consonant production. Mid-sagittal images were recorded by motion imaging techinique during repetitions of CVCV words such as [tata] and [tada]. The measurement of cricoid cartilage position indicated that larynx position was lower in voiced stop [d] than in voiceless stop [t]. Since larynx lowering during voiced obstruents permits airflow from the glottis with a closed vocal tract, it accounts for a mechanism of consonat voicing. This finding along with the result of the first study accounts for acoustic features of CV syllables such that the vowels tend to have lower F0 and formant frequencies when they follow voiced consonants.