Words and pseudowords elicit distinct patterns of 30-Hz EEG responses in humans.

Meaningful words, such as moon, and physically similar but meaningless pseudowords, such as noom, were presented visually in a lexical decision task. The EEG was recorded from 17 scalp electrodes. Significant differences between both stimulus classes were observed in evoked spectral responses of the 'gamma-band' approximately 30 Hz. A hemisphere by wordness interaction demonstrated that 30-Hz spectral power over the left hemisphere was reduced after pseudowords only. These results indicate that gamma-band responses reflect the different cognitive processes induced by words and pseudowords. A possible explanation is the following. Synchronous activation of large cortical cell assemblies takes place after word presentation but not after presentation of pseudowords.