Child acquisition of complex consonants: The role of oral motor control in developing acoustic targets

Our study examines the role of oral motor control in the acquisition of acoustic targets for lingually complex consonants in Estonian by speakers from four age groups. We focus on children's production of secondarily palatalised and non-palatalised consonants where anatomical development and acquisition of motor control skills make differing predictions about the timing and nature of speech production. Our aim is to disentangle the contribution of, on the one hand, speech motor control development and, on the other hand, anatomical growth and articulator change in proportion. We examined oral motor control using a single syllable alternating motion rate diadochokinetic (DDK) task and studied the difference between the second formant (F2) and first formant (F1) using functional principal component analysis. Our results show that palatalised and non-palatalised productions differ significantly across all age groups, indicating children can produce palatalisation contrasts from age 3 years, but consistency in production increases with age. Results also show that children and adults with greater oral motor control skills are better able to produce the palatalisation contrast. These results suggest that anatomical proportions pre-dispose children toward early acquisition of the acoustic properties of palatalisation. However, adult-like production of the phonological contrast also depends on the acquisition of oral motor control skills.