Objective: We recorded vocalization-related cortical fields (VRCF) under complete masking of a subject's own voice to identify the auditory component evoked by a subject's own voice in the VRCF complex.
Methods: We recorded VRCF during simple vowel (/u/) vocalization in 10 right-handed healthy volunteers under two conditions: (1) no masking (control) and (2) masking of the subject's own voice by weighted-white noise during vocalization. In the second experiment, we recorded auditory evoked magnetic fields (AEF) following stimulation of a speech sound applied by voice-recorder.
Results: The onset of VRCF appeared gradually before the vocalization onset, and a clear phase-reversed deflection was identified after the onset of vocalization. The difference waveform obtained by subtracting the VRCF of the masking condition from that of the control showed a deflection (1M) at 81.3+/-20.5 (mean+/-SD) ms after the onset of vocalization, but there was no consistent deflection before the vocalization onset. The AEF following voice sound in the second experiment showed the M100 component at 94.3+/-18.4 ms. The equivalent current dipole of the 1M component for different waveforms was located close in the auditory cortex to that of the M100 for AEF waveforms in each hemisphere.
Conclusion: We successfully separated the auditory feedback response from the VRCF complex, using an adequate masking condition during vocalization of a subject's own voice. The masking effect was crucial to the auditory feedback process after the onset of vocalization. The present results suggested that the 1M component was mainly generated from the auditory feedback process by the subject's own voice. The activated auditory area for simple own voice might be similar to that for simple external sound.