The differential development of vowel context effects on sibilant fricatives

Abstract

Previous work has found that vowel-context effects on the static acoustic properties of sibilant fricatives weaken as children age. The current study extended this prior work by analyzing the development of context effects on the spectral dynamics of English sibilants. Native adults and children (2 through 5 years old) produced /s, ʃ/ in a range of pre-vocalic contexts (/i, e, ɑ, o, u/). Effects of vowel rounding and vowel height were investigated through two pyschoacoustic measures computed from auditory spectra: peak ERB number and excitation drop (difference between maximum high-band and minimum low-band excitation). These measures were estimated from 17 20-ms windows spaced evenly across each production. Effects of vowel context on the intercept and shape of the resulting 17-point trajectories were analyzed with polynomial growth-curve models. Context effects were found to differentially weaken or strengthen in children depending on whether it was the intercept or the shape of the trajectory that was affected. For both sibilants, rounding and height effects on the peak-ERB and excitation-drop intercepts generally weakened with age; whereas, height effects on the shape factors of both trajectories tended to strengthen with age. Future work will extend the analysis to Japanese /s, ɕ/.