The relationship between articulatory control and improved phonemic accuracy in childhood apraxia of speech: a longitudinal case study

Abstract

Jaw movement patterns were examined longitudinally in a 3-year-old male with childhood apraxia of speech (CAS) and compared with a typically developing control group. The child with CAS was followed for 8 months, until he began accurately and consistently producing the bilabial phonemes /p/, /b/, and /m/. A movement tracking system was used to study jaw duration, displacement, velocity, and stability. A transcription analysis determined the percentage of phoneme errors and consistency. Results showed phoneme-specific changes which included increases in jaw velocity and stability over time, as well as decreases in duration. Kinematic parameters became more similar to patterns seen in the controls during final sessions where tokens were produced most accurately and consistently. Closing velocity and stability, however, were the only measures to fall within a 95% confidence interval established for the controls across all three target phonemes. These findings suggest that motor processes may differ between children with CAS and their typically developing peers.

Figure 1

Kinematic traces of jaw velocity and jaw displacement corresponding to the utterance /pαp/ (‘Pop’). Duration measures were based upon peak velocity points. For example, jaw movement duration was calculated from the peak velocity for word initial /p/ to the peak velocity for word final /p/ (marked by the dotted lines). Displacement measures were based on maximum displacement points. For example, displacement into oral opening was measured from the maximum closing movement for /p/ to the maximum opening movement for /a/ (points a to b). Displacement into oral closing was measured from the maximum opening for /a/ to the maximum closing for /p/ (points b to c).

Figure 2

Normalized jaw movement trajectories and corresponding STIs associated with utterance /pαp/ (‘Pop’) produced by the child with CAS (at Time 1 and Time 9) and by a control participant.

Figure 3

Mean displacement and standard error of jaw movement into oral opening and closing in the child with CAS across sessions (T1 to T10) and in the control group. Opening and closing displacements associated with the productions of ‘Mom’, ‘Bob’, and ‘Pop’ are shown separately. The mean and a 95% confidence interval are displayed for the control group.

Figure 4

Mean peak velocity and standard error of jaw movement into oral opening and closing in the child with CAS across sessions (T1 to T10) and in the control group. Peak velocities associated with the productions of ‘Mom’, ‘Bob’, and ‘Pop’ are shown separately. The mean and a 95% confidence interval are displayed for the control group. The asterisk (*) indicates a significant difference from Time 1 (T1) in the child with CAS, p < .01.

Figure 5

Mean STI in the child with CAS across sessions (T1 to T10) and in the control group. STIs associated with the productions of ‘Mom’, ‘Bob’, and ‘Pop’ are shown separately. The mean STI and a 95% confidence interval are displayed for the control group. The asterisk (*) indicates a significant difference from Time 1 (T1) in the child with CAS, p < .01.