Examining speech motor planning difficulties in apraxia of speech and aphasia via the sequential production of phonetically similar words

ABSTRACT

This study investigated the underlying nature of apraxia of speech (AOS) by testing two competing hypotheses. The Reduced Buffer Capacity Hypothesis argues that people with AOS can plan speech only one syllable at a time Rogers and Storkel [1999. Planning speech one syllable at a time: The reduced buffer capacity hypothesis in apraxia of speech. Aphasiology, 13(9–11), 793–805. https://doi.org/10.1080/026870399401885]. The Program Retrieval Deficit Hypothesis states that selecting a motor programme is difficult in face of competition from other simultaneously activated programmes Mailend and Maas [2013. Speech motor programming in apraxia of speech: Evidence from a delayed picture-word interference task. American Journal of Speech-Language Pathology, 22(2), S380–S396. https://doi.org/10.1044/1058-0360(2013/12-0101)]. Speakers with AOS and aphasia, aphasia without AOS, and unimpaired controls were asked to prepare and hold a two-word utterance until a go-signal prompted a spoken response. Phonetic similarity between target words was manipulated. Speakers with AOS had longer reaction times in conditions with two similar words compared to two identical words. The Control and the Aphasia group did not show this effect. These results suggest that speakers with AOS need additional processing time to retrieve target words when multiple motor programmes are simultaneously activated.

KEYWORDS:

• Apraxia of speech
• aphasia
• language production
• speech motor planning
• reaction time

Acknowledgements

Research reported in this publication was supported by the National Institute On Deafness And Other Communication Disorders of the National Institutes of Health under Award Number F31DC014375 and it was completed as part of the first author's doctoral dissertation at the University of Arizona. We would like to thank Fabiane Hirsch, Lisa Jackson, Kindle Rising, Chelsea Bayley, Janet Hawley, and Andrew DeMarco, Cailey Busker, and Patrice Moritz. Finally, we thank our participants for offering their time and cooperation in support of this research.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Notes

1 Two participants with AOS (AOS 001 and AOS 005) also had a diagnosis of dysarthria (AOS 003 had to be excluded due to lack of correct responses as explained above). To evaluate dysarthria as a possible confounding factor, the linear mixed effects models were also run without these two people. Results remained unchanged in terms of the reported significant effects.

Additional information

Funding

This work was supported by National Institute on Deafness and Other Communication Disorders [grant number F31DC014375].