Kinematic measurements of diadochokinetic performances in children with Developmental Apraxia of Speech or Phonological Disorder

Abstract

Children with Developmental Apraxia of Speech (DAS) are known for their difficulties with motor planning and programming of their speech. Children with Phonological Disorder (PD)have prolems with with phonological encoding. Both pathological speech groups experience difficulties in articulation.The purpose of this study was to investigate their articulatory movement of the lower lip while closing for [pa] in mono- and multisyllable utterances and distinguish these two groups on the basis of kinematics. 10 children with speech disorders were divided into subgroups according to severity of sequencing difficulties: correct-ptk group vs. no-ptk group (based upon (un)successful performances of [pataka] utterance), and compared to normally speaking age-matched controls (ages 5;11-9;08).Emma-measurements were taken of lower lip closing movements for [pa] in mono-, bi-, and trisyllabic utterances.The collected data of closing movement existed of displacement, peak velocity,closing duration and their mathematical derivatives.The pathological groups showed larger lip closing movements and faster velocities than the control group. The pathological groups, especially, no-ptk, produced more variability in closing movements and velocities, but less variability in the stiffness coefficient as compared to controls. Variability in kinematics seems to indicate the inability to endure a stable pattern that will facilitate (repetitive) speech. The stiffness coeffcient, a dynamic parameter, represents flexibility, which contributes to adaptive articulatory behaviour needed for demanding speech situations. The pathological groups, the no-ptk group to a higher extent than the correct-ptk group, showed a fairly rigid pattern of dynamics over time. This can be interpreted to indicate that underlying control processes are less flexible as required for skilful articulatory movements and, therefore, less able to adapt to demanding speech tasks.