Formulaic language resources may help overcome difficulties in speech-motor planning after stroke

Abstract

Purpose 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. Methods 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.,/gu:/) 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:/gu:/, based on formulaic phrase “Guten Morgen”; unstereotyped prompt:/mu:/, 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. Results 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). Conclusions 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.