Treating apraxia of speech with an implicit protocol that activates speech motor areas via inner speech

Abstract

Background: Treatments of apraxia of speech (AOS) have traditionally relied on overt practice. One alternative to this method is implicit phoneme manipulation which was derived from early models on inner speech. Implicit phoneme manipulation requires the participant to covertly move and combine phonemes to form a new word. This process engages a system of self-monitoring which is referred to as fully conscious inner speech.

Aims: The present study aims to advance the understanding and validity of a new treatment for AOS, implicit phoneme manipulation. Tasks were designed to answer the following questions. (1) Would the practice of implicit phoneme manipulation improve the overt production of complex consonant blends in words? (2) Would this improvement generalise to untrained complex and simpler consonant blends in words? (3) Would these treatment tasks activate regions known to support motor planning and programming as verified by functional magnetic resonance imaging (fMRI)?

Method & Procedures: The participant was asked to covertly manipulate phonemes to create a new word and to associate this newly formed word to a target picture among four phonologically related choices. To avoid overt practice, probes were collected only after each block of training was completed. Probe sessions assessed the effects of implicit practice on the overt production of simple and complex consonant blends in words. An imaging protocol compared semantic baseline tasks to treatment tasks to verify that implicit phoneme manipulation activated brain regions of interest.

Outcomes & Results: Behavioural: Response to implicit training of complex consonant blends resulted in improvements which were maintained 6 weeks after treatment. Further, this treatment generalised to simpler consonant blends in words. Imaging: Functional imaging during implicit phoneme manipulation showed significant activation in brain regions responsible for phonological processing when compared to the baseline semantic task.

Conclusions: Implicit phoneme manipulation offers an alternative to traditional methods that require overt production for treatment of AOS. Additionally, this implicit treatment method was shown to activate neural areas known to be involved in phonological processing, motor planning, and programming.

Keywords:

• Apraxia
• Inner speech
• Implicit treatment
• Motor speech
• fMRI
• AOS

We acknowledge the support in part by the National Institutes of Health [grant number NIDCD R03 DC010878 to SMW]