Stuttering is a disorder of speech with a prevalence estimated to be 1 % of the world's population of school-age children. It is often a significant communicative problem for the individual, limiting educational and employment opportunities and social and psychological adjustment. The etiology of stuttering is unknown, and standardized, successful treatments for stuttering have not been developed. A major impediment to understanding the etiology of stuttering and to the development of successful therapeutic techniques is the lack of understanding of the physiological bases of the disorder. Stuttering manifests itself as a breakdown in speech motor processes. The complex variables known to affect the occurrence of stuttering, such as emotional state or linguistic complexity, must ultimately have an effect on the physiological events necessary for the production of speech. Therefore, to understand stuttering it is essential to understand the physiological mechanisms underlying disruptions of speech motor processes in stuttering. The research proposed in the present application addresses this general question: What is the nature of the movement disorder associated with stuttering? The specific aims are (1) to determine whether motor processes show evidence of continuous, underlying disturbances in stutterers' speech, (2) to assess whether failures in speech movement control in stuttering are related to autonomic nervous system activity and/or to metabolic respiratory control, (3) to develop new metrics for the analysis of physiological signals related to speech and to apply these new metrics to the assessment of stuttering, and (4) to develop pattern recognition algorithms to determine if there is a consistent set of physiological events associated with stuttering. The results of the proposed studies and those completed in the past years of this project should help us to understand the complex human behavior that is stuttering. In addition, work on this project has significant implications for the study of normal speech production and a variety of motor speech disorders that occur in neurologically impaired individuals.