The context for this study is an exhaustive empirical examination of a research-based and computer-managed treatment for adult developmental stuttering known as the Modifying Phonation Intervals (MPI) program. Within that context, the studies described in this proposal will test a number of hypotheses concerning the relationships among several critical factors: stuttering behavior, the neurology of stuttering, the cognitive and affective components of stuttering, stuttering treatment approaches, and the maintenance of stuttering treatment gains. Thus, this proposal simultaneously addresses two overwhelming needs: efficacious stuttering treatments for adults, and the integration of basic knowledge, such as knowledge about the neurology of stuttering, with information from treatment research to develop comprehensive neurophysiologic and behavioral models of stuttering and stuttering treatment. It is hypothesized that (a) a necessary prerequisite for durable treatment benefits is normalized cerebral blood flow within regions that constitute an emerging model of the neurophysiology of stuttering, and (b) this result can be achieved by establishing a speech pattern that requires the production of speech with a reduced proportion of short phonated intervals (Pis). These aims will be met in a treatment comparison study that employs repeated behavioral, cognitive, and affective evaluations derived from the MPI program and a prolonged speech (PS) program that represents the current standard of care for adult stuttering. This evaluation format will be conjoined by repeated PET scanning, to identify specific speech-motor and neural system changes generated by these treatments and described by an empirically derived stuttering system model. Both treatments include identical transfer and maintenance components plus within- and beyond-clinic assessments that extend over the course of treatment and 12 months after its cessation. Repeated performance-correlation analyses of the derived brain imaging data will test the principal theoretic proposition that the system model regions functionally control the efficacy of stuttering treatment. The overall study also constitutes a Phase II treatment efficacy study that will determine the need for a Phase III treatment trial of the MPI program.