The effects of coarticulation and morphological complexity on the production of English coda clusters: Acoustic and articulatory evidence from 2-year-olds and adults using ultrasound

• Ultrasound can be successfully employed with 2-year-olds to study speech gestural development.
• Like adults, 2-year-olds show coarticulation effects within coda consonant clusters.
• As for adults, 2-year-olds' articulatory gestures within a coda vary with morphological content.

Most studies of phonological development have explored the acquisition of segments, syllables and words using perceptual/transcription methods. Less is known about the articulatory aspects of early speech, or the development of articulatory-acoustic mapping. Recent research on adult speech finds that coarticulation effects are evidenced in both the acoustics and the articulatory gestures, and suggests tighter coarticulation and less variability for monomorphemic compared to polymorphemic segment sequences. The present study explored phonological context and morphological effects in the speech of five adults and five 2-year-olds, combining acoustic and articulatory analysis from ultrasound recordings. The results show that coarticulation effects are found in the word-final consonant cluster (box) for both adults and children. For children, these were evidenced only in the articulatory data. In addition, both age groups showed differences in tongue height between the monomorphemic (box) and bimorphemic (rocks) clusters, suggesting a possible morphological effect. These findings confirm that ultrasound methods can be successfully employed to explore aspects of early gestural development in children as young as 2, and raise many questions regarding the nature of speech planning processes as a function of lexical versus morphological form.