Effects of Age and Syntactic Complexity on Speech Motor Performance

Purpose: This study investigated the effect of age on articulatory movement and stability in young, middle-age, and older adults. It also examined the potential influence of linguistic complexity on speech motor control across utterances that differed in their length and grammatical complexity. Method: There were 60 participants in 3 age groups: 20-30 years, 40-50 years, and 60-70 years, with equal numbers of men and women in each group. The speakers produced 10 repetitions of 5 different stimuli-each of which included the same bilabial-loaded phrase in different grammatical contexts-while their lip movements were recorded. Results: Participants from the 60-year-old group had significantly longer utterance durations, whereas those from the 20-year-old group had the highest jaw spatiotemporal index (STI) values. There were significant differences in the upper lip STI, displacement, and velocity as well as in vocal intensity for the longer, complex conditions compared with the shorter, phrase-only task. Overall, the differences in performance were minimal across grammatical complexity levels that were equal in length. Conclusion: These findings suggest that speech motor control matures beyond young adulthood and that linguistic complexity in a repetitive task does not appear to have a consistent effect on measures of speech movement.