In Robert Logan's book "The Three Dimensions of Stuttering", he states:
"In their book 'Motor Speech Disorders,' Darley, Aronson and Brown (1975) estimated that fluent speech requires 140,000 neuromuscular events per second of speech. Consider, too, that these events must be programmed, co-ordinated, and performed flawlessly. It is a wonder that stuttering is not the norm and that we do not treat fluent speech as the disorder. These 140,000 events are the final result of input of central and peripheral neurological sites into the muscles of the entire motor speech system. In stutterers, we lack the ability to time this system properly. If, however, we have a second signal, such as someone reciting along with us, we are able to properly synchronize these 140,000 events."