Quantal characteristics and motor control in early child speech

Abstract

In the late babbling and early word stages of development, the vowels that children produce are not as “well formed” as those of adults. Taking into consideration the higher formant frequencies of children's vowels, which follow from their shorter supralaryngeal vocal tracts, one finds, for example, that F1 of an [i] is higher than it should be relative to F2 at ages of approximately 70 weeks. This is presumably a consequence of the shorter length of the child's pharynx relative to the oral cavity (King, 1952). As the child matures, the relative position of F1 and F2 of [i] come closer to the adult model. In addition, there is a greater variability in the formant frequencies of all vowels at earlier ages. This may be a consequence of the child's pharynx not being equal in length to the oral cavity, making vowels like [i] less characteristically “quantal” (Stevens, 1952). This variation may also be due to a lack of motor control. In this study, the relative importance of quantalness versus motor control is assessed by comparing the variability of quantal vowels, such as [i] and [u], with other vowels as a function of age.