[Overton]What Causes Stuttering?

by Valerie Johnston, MS, CCC-SLP

Nobody knows for sure, but current research points to a complex interaction between many different variables: hereditary, physiological and psychological factors, and the environment. In fact, some researchers now view stuttering as a heterogeneous disorder involving multiple risk factors, or causes.

One theory that presents this view is the Demands and Capacities Model. The Demands and Capacities Model was developed to organize relevant information about the onset and development of stuttering in young children, not to explain the origin of stuttering; however, since stuttering is a disease that typically begins in early childhood, it also addresses the cause (or causes) of stuttering.

According to this model, each individual has a unique capacity for producing speech fluently. A person's overall capacity for fluency is determined by the interaction of his abilities in many different areas, which are determined, at least to some extent, by hereditary and physiological factors. Each individual also has a unique set of demands that affect his ability to speak fluently. These demands are imposed either by listeners or himself. When the demands exceed the individual's capacity for fluent speech production, disruption of fluency will occur. If the discrepancy is large enough, stuttering will result.

In order to better understand this model, it is necessary to learn about some of the demands and capacities. Following are some capacities considered to be important for fluent speech production:

Language: Speech begins with thoughts and ideas. Language is the ability to select appropriate words, formulate sentences, and conform to conversational rules to express these thoughts and ideas.

Articulation: Once the words and sentence structures have been chosen, it is necessary to rapidly and accurately produce the muscle movements required to produce the desired utterance.

Voice: Almost simultaneously with articulation the vocal folds must be brought together to produce the voice. In order for speech to be produced fluently, articulation and voicing must be precisely coordinated.

The demands originate from the environment or the individual himself. Typical demands include:

Time pressure: This occurs when listeners, including the speaker, expect a rapid rate of speech. It is frequently observed in "rushed households", fast-paced conversations in which there are many questions and interruptions, and the "demand speech" that parents frequently ask of their children (i.e.: "Tell Grandma what you did today.")

Uncertainty: This affects a person's sense of security and usually occurs when major changes take place in the environment or the emotional atmosphere. Such changes include moves, divorce and unemployment. Uncertainty can also occur when a person is unsure about what to say or how to interact with other people.

Perfectionism: This includes unrealistic expectations for performance and a fear of failure. It can be associated only with speech, or it can encompass a wide array of other areas.

According to the Demands and Capacities Model, normal demands in the presence of deficient capacities or excessive demands in the presence of normal or deficient capacities can cause stuttering. In other words, even if capabilities are adequate, excessive demands can result in stuttering. In addition, stuttering can also develop when capabilities in some a given are reduced, even if demands are not excessive.

The cause of stuttering is still unknown. In fact, more and more often stuttering is being viewed as a syndrome with multiple causes. While not directly answering the etiology question, the likelihood that there are several ways children develop stuttering lends support to the multiple-cause theory.


Fiedler, P. and Standop, R. (1983). Stuttering: Integrating Theory and Practice. Rockville, MD: Aspen Publications.

Starkweather, W., Gottwald, S., and Halfond, M. (1990). Stuttering Prevention: A Clinical Method. Englewood Cliffs, NJ: Prentice Hall.

If you have questions or need more information you can contact me at:

Overton Speech & Language Center, Inc.
Fort Worth, TX
(817) 294-8408


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Copyright 2001 Overton Speech & Language Center, Inc.
Last revised: February 03, 2001