Acoustic properties of /k/ and /t/ in normal and phonologically disordered speech

Anticipatory coarticulation was used as an index of motoric fluency in the pronunciation of velar consonant-vowel sequences in a study of the speech of five subjects: two adults, two normal children and one phonologically disordered child. The latter subject was recorded twice. On the first occasion she fronted all velar consonants to an alveolar place of articulation; on the second (one year later) she had just acquired velar articulations. It was hypothesized that the newly acquired velar articulations of the phonologically disordered child would display less of a vowel effect, as measured by spectral characteristics of the burst and VOT, than would the velars of either the normal children or the adults. The hypothesis was refuted: the phonologically disordered child showed more coarticulation of her velar consonants with the following vowel than any of the normal subjects. She also showed a high degree of coarticulation of initial alveolars, of which there was hardly any evidence among the normal subjects. However, on other recognized indicators of maturity of motor control, namely segment durations and variability, her scores were indicative of a lack of maturity. A reappraisal is suggested of the relationship between coarticulation and motoric fluency of speech.