A theory of neuropsycholinguistic function in stuttering.

A theory of neurolinguistic function is proposed to explain fluency and the production of stuttered and nonstuttered speech disruptions. Central to the theory is the idea that speech involves linguistic and paralinguistic components, each of which is processed by different neural systems that converge on a common output system. Fluent speech requires that these components be integrated in synchrony. When they are dyssynchronous, the result can be either nonstuttered disfluency or stuttering, depending on time pressure. Time pressure is defined as the speaker's need to begin, continue, or accelerate an utterance. Nonstuttered disfluency results when the linguistic and paralinguistic components are dyssynchronous and the speaker is not under time pressure. Stuttering results when the speaker is under time pressure and is relatively unaware of the cause of dyssynchrony. Both of these factors are necessary for the identification of the phenomenon of stuttering. Stuttering is defined as disruption of speech that is experienced by the speaker as a loss of control. The theory presented here accounts for both the disruption and the experienced loss of control.

Validity and reliability of judgments of authentic and simulated stuttering.

This exploratory study was undertaken to determine if the concept has merit that the information by which a stutterer identifies stuttering at time of occurrence is qualitatively different from that by which listeners identify stuttering. If it is not the same, then perceptually equivalent stuttered and nonstuttered speech disruptions should be experienced by the stutterer as qualitatively different, even though recordings of these disruptions would sound alike to listeners. To test this hypothesis a criterion was developed to validate a stutterer's ability to accurately identify her stuttering at time of occurrence. She simulated her own stuttering and then judged acoustical recordings of authentic and simulated samples at five intervals following occurrence. Listener judgments were also obtained. Listeners were able to distinguish simulated and authentic samples with 57% accuracy. The stutterer's judgments were never inaccurate at time of occurrence of a speech disruption, but her accuracy decreased rapidly following occurrence, plateauing at 54%. These results supported the concepts that the production of stuttered and nonstuttered speech disruptions are experienced as being qualitatively different, that the difference is involuntary blockage, that only stutterers can validly recognize this difference, and only when it occurs, and that stuttering is a speaker/production rather than a listener/perceptual disorder.

What is stuttering?

The most definitive evidence about any aspect of stuttering is that listeners are unable to judge unit-by-unit occurrences of it acceptably. This result has been replicated repeatedly in every decade for a half century. Nonetheless, for virtually all research and most clinical practice, stuttering has been defined perceptually as if listeners could identify it accurately. Reasons for this state of affairs and its implications for therapy, theory, and research are analyzed. An alternative speech production definition with its implications is proposed. Further, a diagnostic method of validating authentic stuttering is described, as is an objective for fluency-skill therapy that reduces rather than reinforces avoidance behavior.

Prevention and treatment of stuttering.

Evidence is reviewed that forms the basis for prevention and treatment of stuttering as a problem of motor speech coordination. Simplification of phonatory complexity and retardation of phone rate have been demonstrated experimentally to virtually eliminate stuttering. These invariant relationships are used in rate control and breath stream management procedures to facilitate fluency.

Phone rate and the effective planning time hypothesis of stuttering.

Effects on syllable disfluency and phone rate (duration of phones spoken per minute) were compared in 19 adult stutterers under three reading rate conditions: control; slow normally-spoken-word-syllable timed (WS); and phone-prolongation (PP) matched to WS in syllable rate. Both phone rate and syllable disfluency were progressively reduced from control to WS to PP conditions. These results strongly support the discoordination hypothesis that any condition which facilitates initiation of phonation in coordination with articulation and respiration will reduce stuttering. A broader hypothesis is that effective planning time for voice onset coordinations is the common element that explains the power of retarded phone rate, reduction of phonatory complexity, and rhythm virtually to eliminate stuttering.