Background: Apraxia of speech (AOS) is defined as a disorder of articulatory movements, yet a cohesive account of the movement deficit in AOS appears to be lacking. Kinematic evaluation yields precise and objective information regarding the movement deficit in AOS; however, it is an underutilised technique in AOS assessment and in the planning and delivery of treatment. Clearly defined kinematic features of AOS can potentially play a central role in the identification of treatment targets and in measuring treatment outcomes in AOS.
Aims: The overall goal of this systematic review was to characterise the state of the science pertaining to kinematic features of acquired AOS. Specifically, we aimed to (1) characterise kinematic features that distinguish speech in AOS from healthy controls, and (2) determine how these features may vary as a function of task complexity and speaking condition. Five electronic databases were searched from their start-date up to July 2017 using the key terms AOS and speech kinematics. Two raters independently screened abstracts and full texts for inclusion based on pre-determined criteria. Data regarding participant demographics, study design, methods, and results were extracted and analysed descriptively. Two independent raters used a modified version of the Critical Appraisal Tool for Cross-Sectional Studies (AXIS) to assess the methodological quality of included studies.
Main Contribution: The review yielded a total of 11 studies, including 10 case-control studies and one case study. The results revealed a lack of high-quality literature reporting on the kinematic features of AOS. In broad terms, the small body of existing literature reported increased movement range and duration of the lips, jaw, and tongue, increased movement variability, the presence of silent articulatory attempts, and the influence of increasing stimulus complexity on articulatory precision/execution. While initial studies have been helpful in demonstrating the potential of kinematic evaluation in AOS, future studies with higher-quality methodology and larger sample sizes are needed to better characterise movement-based impairments related to AOS and to facilitate potential clinical applications.
Conclusions: Movement-based evaluation provides a promising avenue for the assessment and treatment of AOS, including potential target-selection and measurement of treatment outcomes.