Visual event-related potentials of dyslexic children to rhyming and nonrhyming stimuli.

In a visual event-related potential (ERP) study, children diagnosed as dyslexic in terms of both age and IQ discrepancy criteria were compared with two contrast groups: poor for age (SLOW) readers and normal reading children with Attention Deficit Disorder (ADD). The children viewed 200 stimulus pairs and judged whether the second stimulus of each pair rhymed with the first. The first stimulus was always a three-letter word, while half of the second stimuli were pronounceable nonsense words and half were real words. Rhyme probability was 50%. The ERP waveforms of the dyslexics were significantly different from those of the ADD group in showing less late negativity. The SLOW group's waveforms more closely paralleled those of the ADD group. The major anomalous feature of the dyslexics' waveform was a pronounced late positive peak (P500), which followed an attenuated N450 peak. Over all groups, the N450 peak was sensitive to the rhyme manipulation, as has been found in adults (Rugg, 1984a, 1984b). Real words and nonsense words produced similar waveforms. Hemispheric effects were found but did not interact with group. Results suggest non-automatic visual cognitive processing of rhyme in dyslexics.