The acquisition of gestural timing

Motor plans are complex and consist not only of constriction location and degree, but also gestural timing. For children to acquire adult-like speech, they need to acquire complex timing relationships that can result in delayed acquisition. To examine this phenomenon, we examined long-distance timing patterns for English liquids, /r, l/, and short-distance timing patterns for fricatives, /θ, s, ʃ/, for 5- and 8-year-olds compared to adults. To examine the long-distance timing of liquids, I used an AV-Gated paradigm where participants saw clips of speech and predicted an upcoming /r/ or /d/ (Exp1a) or upcoming /l/ or /d/ (Exp1b). The results revealed long distance timing sequences for /r/ and /l/, with the timing for /r/ extending to at least five segments prior and /l/ 2 segments prior. However, 5-year-olds exhibited extremely long-distance timing for both /r/ and /l/, while 8-year-olds had longer distance timing for /r/ and /l/, but still not adult-like timing. Results suggest long-distance timing must be acquired. In the second experiment, we examined the dynamic COG of fricatives from 5- and 8-year-olds compared to adults. Dynamic COG results revealed significantly more vowel induced variability for/θ/ for adults than for 5- and 8-year-olds, with similar degrees of variability for /s, ʃ/. Overall, the results suggest that acquisition oftiming increases the relative complexity of acquisition, and that segment specific articulation interferes with acquisition of timing in different ways.