Myoelastic and Aerodynamic Theory
The myoelastic theory states that when the vocal cords are brought together and breath pressure is applied to them, the cords remain closed until the pressure beneath them—the subglottic pressure—is sufficient to push them apart, allowing air to escape and reducing the pressure enough for the muscle tension recoil to pull the folds back together again. Pressure builds up once again until the cords are pushed apart, and the whole cycle keeps repeating itself. The rate at which the cords open and close—the number of cycles per second—determines the pitch of the phonation.
The aerodynamic theory is based on the Bernoulli energy law in fluids. The theory states that when a stream of breath is flowing through the glottis while the arytenoid cartilages are held together by the action of the interarytenoid muscles, a push-pull effect is created on the vocal fold tissues that maintains self-sustained oscillation. The push occurs during glottal opening, when the glottis is convergent, whereas the pull occurs during glottal closing, when the glottis is divergent. During glottal closure, the air flow is cut off until breath pressure pushes the folds apart and the flow starts up again, causing the cycles to repeat. The textbook entitled Myoelastic Aerodynamic Theory of Phonation by Ingo Titze credits Janwillem van den Berg as the originator of the theory and provides detailed mathematical development of the theory.
Famous quotes containing the word theory:
“The weakness of the man who, when his theory works out into a flagrant contradiction of the facts, concludes “So much the worse for the facts: let them be altered,” instead of “So much the worse for my theory.””
—George Bernard Shaw (1856–1950)