Are vowels and consonants processed differently? event-related potential evidence with a delayed letter paradigm

To investigate the neural bases of consonant and vowel processing, event-related potentials(ERPs) were recorded while participants read words and pseudowords in a lexical decision task. The stimuli were displayed in three different conditions:(i) simultaneous presentation of all letters(baseline condition);(ii) presentation of all letters, except that two internal consonants were delayed for 50 msec(consonants-delayed condition); and(iii) presentation of all letters, except that two internal vowels were delayed for 50 msec(vowels-delayed condition). The behavioral results showed that, for words, re sponse times in the consonants-delayed condition were longer than in the vowels-delayed condition, which, in turn, were longer than in the baseline condition. The ERPs showed that, starting as early as 150 msec, words in the consonants-delayed condition produced a larger negativity than words in vowels delayed condition. In addition, there were peak latency differences and amplitude differences in the P150, N250, P325, and N400 components between the baseline and the two letter delayed conditions. We examine the implications of these findings for models of visual-word recognition and reading.