Developmental models of childhood apraxia of speech

Childhood apraxia of speech (CAS) is a highly controversial clinical entity with respect to both clinical signs and underlying neuro-motor deficit. This chapter analyzes the origin of these controversies and offers an alternative clinical approach and direction for research based on a review of the literature and studies conducted in our own laboratory. The review shows evidence for a deficit at each of the psycholinguistic and neuro-motor stages from lexical retrieval to motor execution as the primary, proximal origin of CAS. This lack of convergence together with the reported associations rather than dissociations between psycholinguistic and neuro-motor functions during development forms a serious challenge for the modular view on the cognitive architecture of the infant speech production system. An alternative view on clinical classification, the issue of co-morbidity, and research in speech pathology are discussed based on longitudinal analyses of developmental trajectories. By way of example, a computational modelling study is presented in which characteristics of CAS are simulated by manipulating parameters of the DIVA (Directions Into Velocities of Articulators) model.