Relative alpha desynchronization and synchronization during speech perception

Brain processes elicited by speech were studied in IO right-handed subjects by means of examining the desynchronization and synchronization of the 8-10 Hz and 10-12 Hz EEG alpha frequency bands. The subjects listened to an auditorily presented 5 min text passage. The text was presented both forward and backward. Listening to the text forward elicited alpha desynchronization in both of the frequency bands studied, whereas listening to the same text presented backward elicited synchronization in the 10-12 Hz frequency band only. Listening to the text forward elicited greater desynchronization than listening to the text backward. In the 10-12 Hz frequency band, listening to the text forward elicited desynchronization whereas listening to the same text backward elicited synchronization. This dissociation was not observed in the 8-10 Hz frequency band. The results suggest that the lower and upper alpha bands differ such that the 10-12 Hz frequency band exhibits reactivity to the presence of linguistic content while the 8-10 Hz band shows an unspecific response.