Formant frequencies (F1, F2) of jaw-free versus jaw-fixed vowels in normal and articulatory disordered children.

Formant frequency data were gathered for four English vowels (i, ae, a, u) as produced by 15 male Caucasian subjects. There were 5 moderately articulatory disordered children aged 5.9 to 8.1 yr., 5 normal articulatory children aged 6.8 to 7.0 yr., and 5 normal adults aged 19.3 to 23.1 yr. All groups produced vowels under two conditions including with the mandible unconstrained in a normal or free condition and with the mandible fixed by a bite block. All subjects produced formant patterns within the ranges accepted for normal vowels in both jaw unconstrained and jaw fixed conditions. This finding suggests that articulation is a creative and context-sensitive behavior for normally matured, maturing, and developmentally immature systems. Also, it suggests that, if there are neurophysiological differences between groups, the vowel task is too simple to tease them out. The implication of these findings for consideration of tasks of motor equivalence is discussed.