Lexical Precision Moderates Stroop Interference in Dyslexia and Stuttering

Purpose: The Lexical Quality Hypothesis (LQH) posits that differences in the precision of orthographic, semantic, and phonological word representations affect language processing. While LQH components are typically investigated in reading, their role in resolving cognitive conflict remains unknown. This study applies the construct of lexical precision to the traditional naming Stroop task, a gold-standard to quantify cognitive conflict resolution specifically investigating its influence in dyslexia and stuttering. Method: Stroop interference was measured in 84 neurotypical readers, 50 dyslexic adults and 30 adults who stutter (AWS). All participants completed a naming Stroop task, together with a suite of individual difference measures that were analysed using a Principal Component Analysis, which established measures of phonological precision and lexical precision. Results: The data showed that, on average, dyslexic adults and AWS showed significantly larger Stroop interference effects compared with neurotypical adults. Crucially, the magnitude of the Stroop interference was moderated by lexical precision. Dyslexic adults and AWS who scored higher on the lexical precision component showed Stroop interference levels similar to the neurotypical adults, while those with lower precision demonstrated a significantly larger Stroop interference. However, the level of Stroop interference did not differ between AWS and dyslexic adults. Conclusions: The results indicate that an imprecise lexical representation underpins the difficulties in cognitive control mechanisms that are independent of the specific neurodivergent groups.