Event-related brain potentials elicited during phonological processing differentiate subgroups of reading disabled adolescents.

Visual and auditory rhyme judgment tasks were administered to adolescent dyslexics and normal readers while event-related brain potentials were recorded. Reading disabled subjects were split into two groups based on a median split of scores on a visual non-word decoding test. The better decoders were called Phonetics and the poorer decoders were referred to as Dysphonetics. Single syllable, real word stimuli were used, and both rhyming and non-rhyming targets had a 50% chance for matching orthography. In the visual paradigm the normal readers exhibited a left frontal CNV before targets, a large reduction in frontal N400 for matching orthography (orthographic priming), and a large reduction in parietal N400 for rhyming targets (phonological priming). Dysphonetics had an intact CNV and orthographic priming, but the group's phonological priming was very reduced. Phonetics showed both orthographic and phonological priming but had a marked reduction in their CNV. In the auditory task, controls showed a left parietal N400 priming effect for rhyming targets. Dysphonetics showed a similar bilateral effect. The Phonetics did not show a normal priming effect, but produced evidence for priming at a longer latency. Additionally, the Phonetic group responded more slowly than either of the other two groups, who responded with similar latencies. These results support the separation of the reading disabled into a group that has difficulty translating orthography into phonology, and a group that is slower functioning and has reduced capacity in preparing for a response.