THE TEST OF TIME: USING MOTOR SPEECH TIMING ERRORS TO DIFFERENTIATE CHILDREN WITH AND WITHOUT SPEECH SOUND DISORDERS

Abstract

Purpose: The current study investigates relative and absolute motor speech timing errors in children with typically developing speech production (TD), Childhood Apraxia of Speech (CAS) and Phonological Disorder (PD). The study’s overarching goal is to examine these speech timing errors as a potential objective measure for differential diagnosis of Speech Sound Disorders (SSDs). Timing is a critical aspect of motor planning, and it is assumed that CAS is a speech motor planning impairment. However, it is not clear whether the errors of children with other SSDs, such as PD, are a result of additional influence by imprecise speech-motor control, and therefore whether these children would also show greater timing errors. We predicted three outcomes: (1) Adults will show smaller timing errors than children for both absolute timing and relative timing, (2) the SSD group will have larger timing errors than the TD group, and (3) children with CAS are the only children who will show differences from the control (TD) group on these timing error measures. Method: This retrospective study examined timing accuracy based on speech samples obtained at the phrase level from 10 adults, 21 typically developing (TD) children, and 12 children with SSD. Samples (brief phrases containing novel words) were elicited via a repetition task following prerecorded models. Data was abstracted from the acoustic record and analyzed to determine the accuracy of relative timing (PROP) and absolute timing (E). Each timing error measure was averaged for each speaker across sessions and blocks by fricative and vowel. The results of each of these measurements quantified the extent in which a generalized motor program (GMP) and its manipulations (parameters) deviate from the target production (represented by the prerecorded model). Results: Children with SSDs demonstrated significantly higher values of absolute and relative timing error than typically-developing children, suggesting either delayed or disordered speech-motor timing control. As a group, children with CAS (but not children with non-CAS SSD) had larger timing errors than the TD children, suggesting that the group effect (SSD > TD) was driven largely by the children with CAS. However, individual analyses revealed high variability in groups. Conclusions: Measures of relative and absolute timing error at the phrase level during a repetition task may capture aspects of speech motor control in adults, typically developing children, and children with SSDs. Future research with larger sample sizes and longitudinal designs is needed to determine: (1) how relative and absolute timing control develop as children stabilize speech motor control, (2) the degree in which children with SSD deviate from the typical development of these measures, and (3) whether or not these measures are sensitive enough to be a potential objective measure of children with CAS.