An investigation of motor control for speech in phonologically delayed children, normally developing children and adults.

Abstract

Difficulty with phonological acquisition in children is currently widely regarded as a linguistic/cognitive disability but, since speech is a motor as well as a linguistic activity, speech motor control abilities must have a bearing on acquisition of the speech sound system. On the basis of previous studies, measures of speech rate and temporal variability are regarded as indices of level of speech motor control ability.

Evidence was sought concerning the possibility that slow maturation of speech motor control abilities may underlie phonological delay in children. Speech timing characteristics were compared in 12 adult speakers (Group A), 12 normal preschool children (Group N, aged 3;8 years -4;10 years, mean age 4;3 years) and 12 age-matched phenologically delayed children {Group P). Measurements were made of phrase and segment durations and temporal variability in multiple tokens of an experimental phrase. The phonological structure of the speech data was also analysed and a measure of speech rate {in segments/second) was derived.

The N Group were found to exhibit slower speech rates, generally longer mean phrase and segment durations and higher levels of temporal variability than the A Group. The P Group exhibited significantly slower speech rates than the N Group and there was a trend towards longer phrase and segment durations in the P Group data. With one marginal exception, no significant differences were found between the two child groups on measures of temporal variability. The weight of evidence indicated that speech motor control was less mature in the P Group than in the N Group. The findings lend some support to the view that differences in speech motor maturity may be implicated in phonological acquisition differences. Some implications for the design of therapy procedures are explored. The importance of analysing and taking account of the phonological form of speech data in investigations of speech rate is highlighted.