Event-related potentials in silent speech.

Event-related potentials (ERPs) in silent speech using the vowel /a/ were recorded from 12 scalp electrodes and three electrodes monitoring eye and throat movements in eight subjects cued by one of two randomly lit light-emitting diodes (LEDs). The average silent-speech potential minus nonsilent-speech potential showed two significant scalp potential distributions--a positive difference in the occipital scalp area at a 0.30-s latency from the LED onset and a negative difference in the frontal scalp area peaking at electrode Fz at a 0.42-s latency. The occipital scalp potential may include an endogenous component like P3. Possible sites of neural activities underlying the frontal negative difference are discussed in relation to the topography of the scalp potential and functions involved in silent speech.