Differential effects of overt, covert and replayed speech on vowel-evoked responses of the human auditory cortex

Recent magnetoencephalographic studies showed that speaking dampens voice-e voked activity in the human auditory cortex. To further characterize this a udio-vocal interaction, neuromagnetic responses to short tape-recorded prob e vowels were measured while subjects were vocalizing long (8 s) 'backgroun d' vowels either aloud or silently, or while both probe and background vowe ls were replayed from tape. Auditory cortex responses peaking at 100 ms (M1 00) were delayed and dampened bilaterally relative to a background-free con trol during both overtly spoken and replayed long vowels, identifying audit ory interference as the main cause for these modifications. During covert s peech M100 peaked later for matching than non-matching probe/background vow els in the speech-dominant left hemisphere. Thus, voiceless 'inner' speakin g is sufficient to modify utterance-specific processing in the hu man audit ory cortex. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.