WORDS AND PSEUDOWORDS ELICIT DISTINCT PATTERNS OF 30-HZ EEG RESPONSESIN HUMANS

Meaningful words, such as moon, and physically similar but meaningless pseudowords, such as noom, were presented visually in a lexical decis ion task. The EEG was recorded from 17 scalp electrodes. Significant d ifferences between both stimulus classes were observed in evoked spect ral responses of the 'gamma-band' similar to 30 Hz. A hemisphere by wo rdness interaction demonstrated that 30-Hz spectral power over the lef t hemisphere was reduced after pseudowords only. These results indicat e that gamma-band responses reflect the different cognitive processes induced by words and pseudowords. A possible explanation is the follow ing. Synchronous activation. of large cortical cell assemblies takes p lace after word presentation but not after presentation of pseudowords .