Speech planning as an index of speech motor control maturity

This paper investigates speech motor control maturity in 4year-old Canadian French children. Acoustic and ultrasound data recorded from four children, and for comparison, from four adults, are presented and analyzed. Maturity of speech motor control is assessed by measuring two characteristics: token-to-token variability of isolated vowels, as a measure of motor control accuracy, and extra-syllabic anticipatory coarticulation within V1-C-V2 sequences. In line with theories of optimal motor control, anticipatory coarticulation is assumed to be based on the use of internal models of the speech apparatus and its efficiency is considered to reflect the maturity of these representations. In agreement with former studies, token-to-token variability is larger in children than in adults. An anticipation of V2 in V1 was found in all adults but in none of the children studied so far. These results indicate that children's speech motor control is immature from two perspectives: insufficiently accurate motor control patterns for vowel production, and inability to anticipate forthcoming gestures. Both aspects are discussed and interpreted in the context of the immaturity of the internal representations of the speech motor apparatus in 4-year-old children.