Our research uses varied approaches to determine factors that influence speech disorders, including deficits associated with development and those that accompany neurological disease. The techniques employed include acoustic analysis, evaluation of subjects’ auditory and tactile perception, as well as physiological parameters that influence speech production. A general issue that is explored throughout our research is how variability and consistency influence speech production in children and adults. Sources of variation emanate from both sensory and motor aspects of speech. Recent studies suggest that certain indices of variability have facilitative effects on speech learning, whereas other types of variability inhibit speech acquisition or change.