Metrical effects on speech movements in children and adults.

The present study investigates motor processes underlying the production of iambic and trochaic metrical forms for children and adults. Lower lip movement was recorded while 16 children between the ages of 3;10 and 4;9 (years; months) and 8 adults produced iambic (e.g., [see text]) and trochaic (e.g., [see text]) nonce words. For both children and adults, movement patterns for iambic and trochaic words are well differentiated, but in qualitatively different ways. Most notably, children do not produce amplitude modulated forms for trochees, perhaps reflecting a reliance on early developing rhythmic patterns such as those seen in canonical babbling. In contrast, movements corresponding to iambs are well modulated and particularly stable for both groups of speakers, suggesting that they require increased movement specificity. It appears that metrical forms are perceptually and linguistically established and that the child finds the means available within his or her existent motor repertoire to produce adequately differentiated movements corresponding with iambs and trochees.