Kalveram, K.Th., & Natke, U. (1998) "Audiophonatory coupling" links stuttering to linguistic and motor factors in speech production. In E.C. Healey & H.F.M. Peters (Eds.) Proceedings of the 2nd World Congress on Fluency Disorders. The International Fluency Association, 29-35.
Audiophonatory coupling (APC) means that the begin of the phonation of the vowel of a syllable, auditorily fed back, shortens the duration of the generated vowel. In normal speakers, coupling strength, that is the shortening effect, concentrates on the stressed syllable of a word, whereas in people who stutter in addition to the stressed syllable also the unstressed syllables are affected. This indicates that in people who stutter automation of the motor control of the vowel generation in the unstressed syllables are not as successful as in nonstuttering people. Such a lack in automation of phonation control in turn can generalize, and then cause prolongations, which occur firstly at an age of 4 to 5 years. As a reaction, contra-productive methods to stop phonation are likely to be learned. These low level disturbances then influence high level control of speech in such a manner, that either speech blocks or repetitions must occur, as shown in simulation experiments. Taken together, these findings can explain how prosodic and even higher order linguistic features are connected with low level motor control of speaking, and therefore also affect fluency.