Human speech arises from orchestrated activities of phonatory and articulatory organs and reflects human-specific characteristics in anatomy and physiology. The tongue and larynx are less tightly coupled in humans, and they are also innervated separately from the cortex. These biological specificities provide aerodynamic and acoustic bases of speech production and contribute to generating a parallel time-pattern of gradually changing vocal signals with ripples in amplitude and spectrum due to rapid articulatory movements. A close look at local sound variations suggests that tongue-larynx linkage still exists as an old trait common to the primate family, as seen in the variation of vocal frequency due to articulation. Contrarily, articulatory control may also be influenced by laryngeal control, as seen in irregular articulation in certain vocal expressions. Vowel devoicing may be a complex case of such bilateral interactions, and a special attention was made on the topic in this report.