Recognition Memory for High- and Low-Frequency Words in Adult Normal and Dyslexic Readers: An Event-Related Brain Potential Study

Differences in word processing between adult developmental dyslexic (n = 12) and normal readers (n = 12) were studied using event-related brain potentials recorded while subjects performed a recognition memory task. During the first part of the experiment, words were presented consecutively, and within this phase one third of the words were repeated. Subjects had to indicate whether a given word had previously been seen or not. After a delay of 1 hr, a second phase was administered. Here, another list containing 33% old words (presented in Phase 1) and 66% new words was shown and an old/new decision was required. In both categories, half of the words presented in either phase were of high normative frequency, and the other half were of low-frequency in the German language. Recognition performance was superior in normal readers for both high- and low-frequency words. In Phase 1, a fronto-centrally distributed N400 repetition effect discriminated between correctly identified old and new words (new words more negative). This effect was present for dyslexic as well as normal readers and for high- and low-frequency words. Between 450 and 800 ms, a 'P600 old/new effect' emerged (ERPs evoked by old words were more positive than those for new words). This effect was larger for low-frequency words. In Phase 2, an old/new effect was obtained for normal readers only. These findings are discussed in relation to current concepts of dyslexia and of semantic processing.