What anticipatory coarticulation in children tells us about speech motor control maturity

PURPOSE: This study aimed to evaluate the role of motor control immaturity in the speech production characteristics of 4-year-old children, compared to adults. Specifically, two indices were examined: trial-to-trial variability, which is assumed to be linked to motor control accuracy, and anticipatory extra-syllabic vowel-to-vowel coarticulation, which is assumed to be linked to the comprehensiveness, maturity and efficiency of sensorimotor representations in the central nervous system. METHOD: Acoustic and articulatory (ultrasound) data were recorded for 20 children and 10 adults, all native speakers of Canadian French, during the production of isolated vowels and vowel-consonant-vowel (V(1)-C-V(2)) sequences. Trial-to-trial variability was measured in isolated vowels. Extra-syllabic anticipatory coarticulation was assessed in V(1)-C-V(2) sequences by measuring the patterns of variability of V(1) associated with variations in V(2). Acoustic data were reported for all subjects and articulatory data, for a subset of 6 children and 2 adults. RESULTS: Trial-to-trial variability was significantly larger in children. Systematic and significant anticipation of V(2) in V(1) was always found in adults, but was rare in children. Significant anticipation was observed in children only when V(1) was /a/, and only along the antero-posterior dimension, with a much smaller magnitude than in adults. A closer analysis of individual speakers revealed that some children showed adult-like anticipation along this dimension, whereas the majority did not. CONCLUSION: The larger trial-to-trial variability and the lack of anticipatory behavior in most children—two phenomena that have been observed in several non-speech motor tasks—support the hypothesis that motor control immaturity may explain a large part of the differences observed between speech production in adults and 4-year-old children, apart from other causes that may be linked with language development.