Bruce L. Smith
Mary Kay Kennedy
Dept. of Commun. Sci. and Disord., Northwestern Univ., 2299 North Campus Dr., Evanston, IL 60208-3570
A number of cross-sectional studies have observed that children's speech segments tend to decrease in duration and also become less variable from younger to older groups of subjects. Because cross-sectional investigations have certain limitations when they are used to study children's development, it is also important to conduct longitudinal analyses of speech production development. The present study provides data based on a longitudinal analysis of the speech of 12 children. When they were initially seen, the children ranged from 7--11 years of age; they were evaluated again after approximately 1--1/2 years. At both ages, the children were recorded as they produced 25 repetitions of each of several different words and short phrases, from which various segments and syllables were measured. Results indicate that, on average, segment and syllable durations decreased from the initial to the follow-up recordings by approximately 10%, whereas temporal variability was found to decrease by about 40%. Although the relative decrease in the children's temporal variability was substantially greater than the decrease in their duration across the year-and-a-half time period, their durations were considerably more adultlike than their variability at both times they were studied.