A longitudinal study of the development of temporal properties of speech production: data from 4 children.

A general conclusion that has emerged from the collective results of a number of studies regarding acoustic characteristics of children's speech production development is that both the duration and temporal variability of segments, words, and phrases tend to decrease as one considers increasingly older groups of children. While this conclusion is largely appropriate when considering averages for groups of children studied across intervals of several years, the limited amount of longitudinal data that exists suggests that similar patterns may not routinely be observed in the development of individual children, especially when shorter time periods are involved. Cross-sectional, acoustic studies have provided important general descriptions of speech production development, but additional longitudinal investigations are also needed to address issues that cannot be effectively evaluated utilizing cross-sectional data. For example, it was hypothesized in the present study that decreases in duration and variability would be greater when children were younger and that progressively smaller decreases would occur as they became older. Despite general tendencies for decreases in duration and variability to occur with increased age, it was also hypothesized that not all segments and words would be affected to the same extent in this regard. To consider these and related questions, the speech of 4 children was recorded approximately every 7-10 months for periods ranging from 4 to 6 years. There was some support for the notion that duration/variability decreases were greater when children were younger, but often this was not observed. It was also found that whereas some sounds/words decreased in duration across time, others remained relatively constant. Also, within the same word, certain segments became shorter across time, while others remained unchanged. These observations provide a perspective concerning speech production development that represents an important supplement to more general conclusions that have been obtained from group-oriented studies.