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Primary objective: Electromagnetic articulography was employed to investigate the strength of articulatory coupling and hence the degree of functional movement independence between individual articulators in apraxia of speech (AOS). Methods and procedures: Tongue-tip, tongue-back and jaw movement was recorded from five speakers with AOS and a concomitant aphasia (M = 53.6 years; SD = 12.60) during /ta, sa, la, ka/ syllable repetitions, spoken at typical and fastrates of speech. Covariance values were calculated for each articulatory pair to gauge the strength of articulatory coupling. The results obtained for each of the participants with AOS were individually compared to those obtained by a control group (n = 12; M = 52.08 years; SD = 12.52). Comparisons were made between the typical rate productions of the control group and the typical and fast rate productions of the participants with AOS.
Main outcomes and results: In comparison to the control group, four speakers with AOS exhibited significantly stronger articulatory coupling for alveolar and/or velar speech targets, during typical and/or fast rate conditions, suggesting decreased functional movement independence.
Conclusions: The reduction in functional movement independence might have reflected an attempt to simplify articulatory control or a decrease in the ability to differentially control distinct articulatory regions