Word Order Processing in Dyslexic adults: Evidence from grammaticality decision tasks

Reading relies on the seamless integration of rapid, automatic word recognition and the structural constraints of word order. Non-dyslexic readers exhibit a transposed word effect (TWE), evidenced by lower accuracy and slower reaction times for stimuli containing word transpositions derived from grammatical, rather than ungrammatical, base sentences. The TWE suggests a reliance on top-down syntactic constraints rather than purely flexible processing. The nature of these constraints in dyslexic adults, however, remains poorly understood. The present study investigated whether dyslexic adults possess the same positional flexibility as non-dyslexic readers, or if their processing is constrained by serial-order impairments. We used parallel, central serial, and progressive displays across three experiments with 372 adults (62 participants per group). Across all display types, we observed a TWE in accuracy and a three-way interaction between group, condition, and display type. Specifically, while non-dyslexic readers showed a larger TWE in the parallel display compared to the central and progressive displays, dyslexic readers exhibited a larger TWE in the central and progressive displays compared to the parallel display. These findings indicate that the TWE is a marker of high cognitive cost linked to noisy, temporally processed orthographic input during sentence-level interpretation.