Inner speech as a mechanism of naming improvement after lexical-semantic therapy in chronic aphasia

Purpose: This study investigates whether inner speech—the mental rehearsal of words without articulation—facilitates naming recovery in individuals with aphasia. We hypothesized that items with preserved inner speech but impaired overt naming at baseline would improve more after speech therapy than items without inner speech. Method: Nineteen participants with chronic, expressive aphasia participated in three pre-treatment naming sessions, nine treatment sessions (semantic feature analysis), and three post-treatment naming sessions. For each pre- and post-treatment naming session, participants named ~300 items (pictures of nouns) aloud and also indicated whether they had inner speech for each item. Based on pre-treatment naming sessions, 30 individualized items (“Treated30”) were trained using semantic feature analysis. Mixed-effects models analyzed the effect of treatment, inner speech, psycholinguistic properties, and aphasia severity on naming outcomes immediately post-treatment. Results: There was an average of 60.8% proportional improvement on overt naming and 41% improvement on inner speech for the Treated30 from baseline to follow-up. In a series of hierarchical mixed models, baseline inner speech, inner speech across the study, aphasia severity, and interactions of inner speech variables with treatment were significant in predicting correct naming post-therapy. Conclusions: Findings suggest a bidirectional relationship between inner and overt speech: baseline inner speech and, importantly, improvements in inner speech significantly influence therapy-related gains in naming. These results suggest that inner speech-focused interventions may improve outcomes by providing a cognitive scaffold for speech production.