The Nature of Phonological Impairments in Dyslexia and Stuttering: Evidence from Phonemic, Semantic, and Design Fluency Tasks

Objective: Verbal fluency requires generating items according to specific rules. While semantic fluency is often preserved in dyslexia and stuttering, phonemic fluency is typically impaired. Most research, however, focuses on total word counts rather than underlying mechanisms. Method: This online study compared 62 dyslexic adults, 62 adults who stutter (AWS), and 62 neurotypical adults using typed verbal fluency and mouse-drawn design fluency tasks. Design fluency assessed whether impairments stemmed from general executive control or specific phonological deficits. Results: Using hierarchical regression, we observed that dyslexia and stuttering predicted lower correct output for phonemic fluency but did not predict scores on the semantic or design fluency tasks. At a finer-grained level, dyslexia and stuttering both predicted a smaller number of switches between subcategories on the phonemic fluency task, whereas stuttering also predicted the size of phonemically-related clusters of items. Conclusion: Overall, these results indicate that the executive fluency impairment found in dyslexia is related to accessing phonological representations, whereas adults who stutter have an impairment in terms of the phonological representation. These findings suggest that despite similar phonological impairments, the phonological mechanisms in dyslexia and stuttering are distinct, necessitating specialized clinical interventions.