ELECTROPHYSIOLOGICAL EVIDENCE FOR CATEGORY-SPECIFIC WORD-PROCESSING IN THE NORMAL HUMAN BRAIN

SELECTIVE impairment of word categories such as nouns vs verbs has suggested a regional representation of lexical knowledge in the human brain. The time course of visual word processing was investigated using event-related potentials (ERPs) in normal adults. Subjects performed a word classification task with five categories of stimuli: animal names, verbs, numerals, proper names and meaningless consonant strings. A bilateral posterior ERP difference between words and consonants first appeared 192 ms following stimulus onset, probably reflecting the construction of the visual word form. Category-specific ERP differences began to appear around 260 ms. There was a left temporo-parietal negativity for animal names and verbs, a left inferior temporal negativity for proper names, and a bilateral positivity for numerals. These results provide a bilateral parietal positivity evidence for timing and coarse localization of category-specific word processing in the normal human brain.