Acoustic quantification of /i/-/I/ overlap in children 21 to 33 months.

This longitudinal investigation examined the temporal and spectral characteristics of the high front vowels /i/ and /I/ as produced by nine monolingual US English children from 21–33 months. Vowel overlap was quantified in two-dimensional (F1, F2) and three-dimensional (F1, F2, duration) space using Spectral Overlap Assessment Measure (SOAM). These findings were compared with the results from Support Vector Machine (SVM) vowel classification, vowel duration ratios, and measures of effect size, to determine whether a spectral/temporal trading effect existed in the early vowel productions of young children. Children between the ages of 21 and 33 months are highly variable in the way they use spectral and temporal parameters to distinguish between these two adjacent vowels. However, findings pointed to the existence of a spectral/temporal trading effect when spectral overlap values are relatively high (>60%) at 21 and 24 months of age.