Theories About Stuttering

Stuttering, or dysfluent speech, likely has more than one cause. Those causes are complex with many interrelated factors. Dysfluency may be caused by improper cortical organization for some, difficulty with auditory processing for others, and by an immature processing system attempting to meet mature demands for still others.

Historical Theories

• Theories about dysfluencies date back to Hippocrates and the ancient Greeks. Hippocrates theorized that stuttering was caused by dryness of the tongue, and he prescribed a series of herbal remedies or surgery to correct it. In the 19th century,

  it was believed that stuttering was caused by an anatomic defect of the oral cavity, and surgery was the treatment of choice. Due to the ineffectiveness of surgery, 20th century physicians theorized that stuttering was psychogenic. Both operant conditioning and psychoanalysis were tried as treatments and both were abandoned in the 1960s as inadequate.

Genetic Causes

• Robert West, a founder of the discipline of speech pathology, observed dysfluency's strong genetic component in the 1930s. Twin studies since that time have reinforced his observations. In 1998, the American Academy of Pediatrics reported that 77 percent of dysfluent monozygotic (identical) twins had a twin who was also dysfluent versus 33 percent of dizygotic (fraternal) twins. In addition, first-degree relatives of stutterers (parents, children and full siblings) were more than three times as likely to experience dysfluency as the general population.

Breakdown Hypotheses

• Some theories assume that dysfluency is caused by a breakdown in either the language center of the brain or in the auditory processing system. The language center of the brain is typically located in the left hemisphere. However, brain scans of children with dysfluencies often reveal that the right hemisphere is overused. When the right hemisphere is not adequately developed for speech, dysfluency can develop as the brain attempts to reorganize itself to better access the resources in the left hemisphere. Another breakdown hypothesis holds that there is a slight delay in auditory processing. This causes an echo effect for the speaker that breaks his concentration and disrupts his timing, resulting in dysfluency.

Demands-Capacity Model

• The demands-capacity model for understanding dysfluency states that there is a mismatch between a child's organic ability to produce speech and the demands placed on her to communicate. Capacity refers to the child's developing ability to produce sounds in the rapid sequences required to produce speech. It includes, motor skills, reaction times, the ability to plan and carry out sequential movements, vocabulary and word-finding skills. Demands can be either internal (desire to communicate or emotional state) or external (pace of conversation or pressure to answer questions). Capacity and demand skills both typically develop at the same time. However, demand exceeds capacity for some children experiencing dysfluency.