Task-related EEG asymmetries: a comparison of alpha blocking and beta enhancement.

Alpha and beta content of spectrally analyzed EEG were used to assess differential hemispheric engagement during two linguistic tasks (semantic and phonetic) and one acoustic task involving detection of target items embedded within the same stimulus series. Beta content of the EEG increased reliably in the left hemisphere during the linguistic tasks, whereas the expected attenuation or blocking of alpha did not occur reliably. These data suggest that left hemisphere beta enhancement rather than alpha blocking is a more efficient index of differential hemispheric engagement during language processing.