Effect of Bite-Block on Oral-Laryngeal Timing in Apraxia of Speech

K Ballard, V Flemmer, J Moon

 

Acquired apraxia of speech (AOS) has been described as an impairment in temporal coordination within and across articulators. Some have hypothesized that this impairment affects remote articulators to a greater degree than proximate articulators. Here, bite-block perturbation was employed to examine the stability and flexibility of coordination across proximate (lips) and remote (larynx) articulators in six healthy adults and one individual with AOS. Displacement and velocity of the lips, voice onset time (VOT), and perceptual accuracy were measured for production of /papa/ and /baba/. With perturbation, control subjects altered displacement and velocity of the lips but maintained VOT thus maintaining high perceptual accuracy. Consistent with prediction, kinematics of proximate articulators (the lips) in the apraxic speaker was similar to controls but temporal coordination across remote articulators (lips and larynx) was disrupted. Perturbation resulted in increased variability of VOT for /p/ and /b/ production in the apraxic speaker, however, perceptual accuracy improved for /p/ but deteriorated for /b/ production. Results suggest that AOS affects the ability to modify parameters of functional units to accommodate changes in initial conditions, which has ramifications for assessment and treatment.