Vowel Imagery Decoding toward Silent Speech BCI Using Extreme Learning Machine with Electroencephalogram

Figure 3

Time-frequency representation (TFR) of EEG signals averaged over all trials for subjects 2 and 5. The EEG signals were obtained from eight electrodes in the left temporal areas during each of the six experimental conditions (vowels /a/, /e/, /i/, /o/, /u/, and mute). The EEG data were bandpass filtered with 1–100 Hz, and a Morlet mother wavelet transform was used to calculate the TFR. The TFRs are plotted for the first 2 s after final beep sound and for the frequency range of 10–70 Hz.