The development of motor synergies in children: ultrasound and acoustic measurements.

The present study focuses on differences in lingual coarticulation between French children and adults. The specific question pursued is whether 4-5 year old children have already acquired a synergy observed in adults in which the tongue back helps the tip in the formation of alveolar consonants. Locus equations, estimated from acoustic and ultrasound imaging data were used to compare coarticulation degree between adults and children and further investigate differences in motor synergy between the front and back parts of the tongue. Results show similar slope and intercept patterns for adults and children in both the acoustic and articulatory domains, with an effect of place of articulation in both groups between alveolar and non-alveolar consonants. These results suggest that 4-5 year old children (1) have learned the motor synergy investigated and (2) have developed a pattern of coarticulatory resistance depending on a consonant place of articulation. Also, results show that acoustic locus equations can be used to gauge the presence of motor synergies in children.