SPATIOTEMPORAL STABILITY OF LIP MOVEMENTS IN OLDER ADULT SPEAKERS

Although the intelligibility of healthy older adults normally seems un impaired, age-related changes occur in sensorimotor components of the speech system and in such global parameters as speech rate. In order t o clarify the effect of these changes on the variability of speech mov ements, we examined oral peripheral abilities, speech rate, and speech kinematics in a group of 10 adults age 76-83, compared to a group of 10 young adults. Participants repeated a short phrase 15 times at habi tual, fast, and slow rates. The resulting lip displacement signals wer e time-and amplitude-normalized, and successive standard deviations al ong the movement waveforms were summed to produce a spatiotemporal ind ex (STI) representing individual variability in movement pattern. Part icipants tended to show greatest variability at slow rate, less variab ility at fast rate, and least variability at habitual rate. For the ol der adults, STI at habitual rate was significantly higher (more variab le) and speech durations were longer than those of young adults. Perio ral strength and tactile acuity were poorer in these older adults than in young adults. We conclude that as sensorimotor abilities change in old age, speakers are less consistent in the spatiotemporal organizat ion of speech movements, reflecting decreased stability of speech moto r control.