Consonant-vowel interdependencies in babbling and early words: preliminary examination of a locus equation approach

Consonant-vowel productions at two distinct stages of language development were studied in a single female child. At 12 months canonical babbling syllables (N = 144) identified by a panel of listeners as comprising [bV], [dV], and [gv] tokens were acoustically analyzed by measuring F2 transition onset and F2 midvowel frequencies and plotting their relationship as locus equations for each stop category. A regression analysis performed on these scatterplots revealed differential slopes and y-intercepts as a function of stop place. The same analysis was performed 9 months later on CV utterances (N = 243) produced as syllable-initial segments of real words by the same child. Whereas labial and velar locus equation parameters moved toward more adult-like values, alveolar slope and y-intercept moved away from adult values and more in the direction of decreased coarticulation between vowel and consonant. There was greater scatter of data points around the regression line for production of words compared to babbling. These results are compared to locus equations obtained from 3-5-year-olds and adults. Locus equations appear to be useful as an empirical developmental probe to document how CV productions gradually approach adult categorical standards.