An investigation of motor equivalence in the speech of children and adults.

Although the concept of motor equivalence (i.e., articulatory intercoordination) is generally accepted as functioning in normal speech production, few studies have experimentally demonstrated its existence. One purpose of the present study was thus to obtain additional data concerning this phenomenon. Because motor equivalence is often assumed to represent a rather sophisticated ability in speakers, another purpose of the study was to determine whether trends could be observed that might demonstrate a developmental progression toward more frequent occurrence of articulatory intercoordination with increasing age. A strain gauge transduction system was used to monitor inferior-superior upper lip, lower lip, and jaw movements produced by a group of adults and three groups of children ranging from 4-11 years of age, as they spoke in a normal condition and in two "perturbed" conditions (bite block and fast rate). Based on the assumption that the presence of a significant negative correlation between two articulators constitutes evidence of articulatory intercoordination, there was little indication of motor equivalence in the speech of the adults or the children.