Investigating the use of a nonspeech task to measure tongue–jaw differentiation: Findings across typical development

Purpose: Clinically, a task of alternating tongue lateralization has been used to evaluate the ability to independently control the tongue and jaw, with jaw movement interpreted as a sign of poor tongue–jaw differentiation. However, there is a lack of normative data regarding jaw movement during this task and whether this changes over the course of development. This study quantified relative tongue and jaw movement during alternating tongue lateralization for typical speakers across age ranges and examined whether degree of jaw movement varies as a function of age. Method: Participants were 39 typical children, adolescents, and adults ranging from 6 to 29 years old. A motion capture system was used to track tongue and jaw movement during an alternating tongue lateralization task, and the average relative contribution of the jaw to tongue lateralization was determined for each participant. Results: Age did not correlate significantly with the average relative contribution of the jaw to tongue lateralization. Typical children, adolescents, and adults exhibited wide variability in the degree of jaw movement during this task. Conclusion: Variability among typical speakers in alternating tongue lateralization performance makes it challenging to determine if/when performance should be considered atypical. Clinical findings from this task must be interpreted with caution. Supplemental Material: https://doi.org/10.23641/asha. 6626222.