Impaired neural discrimination of regular words from pseudowords in dyslexic adults as revealed by fast periodic visual stimulation

Abstract

We used Fast Periodic Visual Stimulation with EEG recordings to assess the sensitivity of adults with dyslexia to fine-grained psycholinguistic variations of letter strings: lexicality and orthographic regularity. Dyslexic and non-dyslexic university students watched 60-s streams of stimuli presented at 10 Hz with deviant items (words) inserted periodically (1/8, at 1.25 Hz). While there was no overall difference in neural response between groups at the base stimulation frequency (10 Hz), individuals with dyslexia showed significantly reduced 1.25 Hz discrimination response for regular and irregular words among pseudowords (lexicality) over the left occipito-temporal cortex. Interestingly, while dyslexic individuals had significant weaker responses for irregular words than normal readers, they did not show any discrimination response for regular words within streams of pseudowords. However, they displayed responses to regularity changes within streams of words, that were not significantly below typical readers’. Overall, these observations suggest that lexical processes are not automatically triggered in dyslexia when a decoding strategy is enhanced by context (i.e., pseudowords) but may be at work when the overall activation of the lexicon is high (i.e., words). The results also show the diagnostic value of the FPVS-EEG approach to determine and characterize reading impairments rapidly, objectively and implicitly.