Mailend, M.-L., Maas, E., Beeson, P., Story, B., Forster, K. (2021). Examining speech motor planning difficulties in apraxia of speech and aphasia via the sequential production of phonetically similar words. Cognitive Neuropsychology 38(1), 72–87.

This study investigated the underlying nature of apraxia of speech via a reaction time experiment. The results showed that people with apraxia of speech have longer reaction times in conditions that required preparing two phonetically similar words for production compared to preparing two identical words. This finding supports the Program Retrieval Deficit Hypothesis: people with apraxia of speech have a difficulty with selecting a motor program for a target word when several motor programs are simultaneously activated.

Mailend, M.-L., & Maas, E. (2020). To Lump or to Split? Possible Subtypes of Apraxia of Speech. Aphasiology 35(4), 592–613.

This paper reviewed possible subtypes of apraxia of speech proposed on the basis of  clinical symptomatology, theoretical constructs, and an analogy to limb apraxia. Several proposed apraxia of speech (AOS) subtypes have found some support in the literature. Further research is needed to determine the validity, coherence and utility of possible AOS subtypes for theoretical and clinical purposes.