Word and pseudoword superiority effects reflected in the ERP waveform.

A variant of the Reicher-Wheeler task was used to determine when in the event-related potential (ERP) waveform indices of word and pseudoword superiority effects might be present, and whether ERP measures of superiority effects correlated with standardized behavioral measures of orthographic fluency and single word reading. ERPs were recorded to briefly presented, masked letter strings that included real words (DARK/PARK), pseudowords (DARL/PARL), nonwords (RDKA/RPKA), and letter-in-xs (DXXX, PXXX) stimuli. Participants decided which of two letters occurred at a given position in the string (here, forced-choice alternatives D and P). Behaviorally, both word (more accurate choices for letters in words than in baseline nonwords or letter-in-xs) and pseudoword (more accurate choices for letters in pseudowords than in baseline conditions) superiority effects were observed. Electrophysiologically, effects of orthographic regularity and familiarity were apparent as early as the P150 time window (100-160ms), an effect of lexicality was observed as early as the N200 time window (160-200ms), and peak amplitude of the N300 and N400 also differentiated word and pseudoword as compared to baseline stimuli. Further, the size of the P150 and N400 ERP word superiority effects was related to standardized behavioral measures of fluency and reading. Results suggest that orthographic fluency is reflected in both lower-level, sublexical, perceptual processing and higher-level, lexical processing in fluently reading adults. Copyright 2010 Elsevier B.V. All rights reserved.