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. We explored the extent to which a change in inner speech across the study supported naming recovery. 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 a significant proportional improvement on overt naming and inner speech for the Treated30 from baseline to follow-up. In a series of mixed models, the most significant predictor was the interaction between treatment and inner speech across the study. Baseline inner speech, on its own, did not significantly predict post-treatment naming outcomes. Conclusions: Findings suggest a bidirectional relationship between inner and overt speech: importantly, improvements in inner speech significantly influence therapy-related gains in naming. Age of acquisition also explained naming outcomes, though to a lesser extent. These results suggest that inner speech-focused interventions may improve outcomes by providing a cognitive scaffold for speech production.