Neuromotor speech impairment: it's all in the talking

The aim of this article is to explicate the uniqueness of the motor activity implied in spoken language production and to emphasize how important it is, from a theoretical and a clinical perspective, to consider the motor events associated with speaking as domain-specific, i.e., as pertaining to the domain of linguistic expression. First, phylogenetic data are reviewed demonstrating the specificity of the human vocal tract motor network regarding (i) the entrenchment of laryngeal motor skills within the organization of vocal tract movements, (ii) the evolution of a neural basis for skill acquisition within this system, and (iii) the integration of this system into an auditory-motor network. Second, ontogenetic evidence and existing knowledge about the experience-dependent plasticity of the brain are reported to explicate that during speech acquisition the vocal tract motor system is constrained by universal properties of speech production and by the specific phonological properties of the speaker's ambient language. Third, clinical data from dysarthria and apraxia of speech provide the background for a discussion about the theoretical underpinnings of domain-general versus domain-specific views of speech motor control. The article ends with a brief sketch of a holistic neurophonetic approach in experimental inquiries, assessment, and treatment of neuromotor speech impairment.