Formulaic Language Resources May Help Overcome Difficulties in Speech-Motor Planning after Stroke.

Abstract

Decades of research have explored communication in cerebrovascular diseases by focusing on formulaic expressions (e.g., "Thank you"-"You're welcome"). This category of utterances is known for engaging primarily right-hemisphere frontotemporal and bilateral subcortical neural networks, explaining why left-hemisphere stroke patients with speech-motor planning disorders often produce formulaic expressions comparatively well. The present proof-of-concept study aims to confirm that using verbal cues derived from formulaic expressions can alleviate word-onset difficulties, one major symptom in apraxia of speech. In a cross-sectional repeated-measures design, 20 individuals with chronic post-stroke apraxia of speech were asked to produce (i) verbal cues (e.g., /guː/) and (ii) subsequent German target words (e.g., "Tanz") with critical onsets (e.g., /t/). Cues differed, most notably, in aspects of formulaicity (e.g., stereotyped prompt: /guː/, based on formulaic phrase "Guten Morgen"; unstereotyped prompt: /muː/, based on non-formulaic control word "Mutig"). Apart from systematic variation in stereotypy and communicative-pragmatic embeddedness possibly associated with holistic language processing, cues were matched for consonant-vowel structure, syllable-transition frequency, noun-verb classification, meter, and articulatory tempo. Statistical analyses revealed significant increases in correctly produced word onsets after verbal cues with distinct features of formulaicity (e.g., stereotyped versus unstereotyped prompts: p < 0.001), as reflected in large effect sizes (Cohen's dz ≤ 2.2). The current results indicate that using preserved formulaic language skills can relieve word-onset difficulties in apraxia of speech. This finding is consistent with a dynamic interplay of left perilesional and right intact language networks in post-stroke rehabilitation and may inspire new treatment strategies for individuals with apraxia of speech.