Speech‐like and non‐speech lip kinematics and coordination in aphasia

BACKGROUND: In addition to the well-known linguistic processing impairments in aphasia, oro-motor skills and articulatory implementation of speech segments are reported to be compromised to some degree in most types of aphasia. AIMS: This study aimed to identify differences in the characteristics and coordination of lip movements in the production of a bilabial closure gesture between speech-like and non-speech tasks in individuals with aphasia and healthy control subjects. METHODS & PROCEDURES: Upper and lower lip movement data were collected for a speech-like and a non-speech task using an AG 100 EMMA system from five individuals with aphasia and five age- and gender-matched control subjects. Each task was produced at two rate conditions (normal and fast), and in a familiar and a less familiar manner. Single articulator kinematic parameters (peak velocity, amplitude, duration and cyclic spatio-temporal index) and multi-articulator coordination indices (average relative phase and variability of relative phase) were measured to characterize lip movements. OUTCOMES & RESULTS: The results showed that when the two lips had similar task goals (bilabial closure) in speech-like and non-speech task, kinematic and coordination characteristics were not found to be different. However, when changes in rate were imposed on the bilabial gesture, only speech-like task showed functional adaptations, indicated by a greater decrease in amplitude and duration at fast rates. In terms of group differences, individuals with aphasia showed smaller amplitudes and longer movement durations for upper lip, higher spatio-temporal variability for both lips, and higher variability in lip coordination than the control speakers. Rate was an important factor in distinguishing the two groups, and individuals with aphasia were limited in implementing the rate changes. CONCLUSIONS & IMPLICATIONS: The findings support the notion of subtle but robust differences in motor control characteristics between individuals with aphasia and the control participants, even in the context of producing bilabial closing gestures for a relatively simple speech-like task. The findings also highlight the functional differences between speech-like and non-speech tasks, despite a common movement coordination goal for bilabial closure.