Often a glottal stop happens at the beginning of vowel phonation after a silence. They aid phonation (speech) by suppressing dysphonia. Therapy directly modifies the abnormal physiologic activity affecting respiration, phonation, and resonance. The cricothyroid muscle is the only tensor muscle of the larynx aiding with phonation. The contrastive mechanism is the vowel phonation. Voiced stops are phonetically voiceless with slack voice phonation in stressed, word initial position. In some languages there are contrasts among vowels with different phonation types. As do other consonants, clicks vary in phonation. It is also the term used in linguistics for the most common phonation of vowels. Sounds are voiced when the vocal folds begin to vibrate in the process of phonation. Along with phonation and articulation, it is one of three main components of speech production. The intrinsic muscles are divided into respiratory and the phonatory muscles (the muscles of phonation). It is this vibratory motion that produces phonation or voice. Alsatian, like several Germanic languages, has a typologically unusual phonation in its stops. They vibrate, modulating the flow of air being expelled from the lungs during phonation.