An Examination of EEG Frequency Components Related to Speech Imagery and Its Identification

Abstract

This study is to examine EEG frequency components relating the intention (“I want to drink”) to “with/without speech imagery” when drink-images are displayed on the PC screen. An experimental process was set in 8 s as followings; fixation image display (1 s), drink image display (2.5 s), intention check (1.5 s), fixation image display (1 s), and speech imagery period (2 s). It was repeated 100 times. EEG was measured with 10-20 system in a magnetically shielded room with BPF (0.08-100 Hz) and notch filter (50 Hz) for 10 subjects. In the analysis, it was averaged with 35 trials dividing between “with/without speech imagery” in an epoch (fixation image display and speech imagery) of 3 s and time-frequency analysis was done. Event-related synchronization (ERS) and desynchronization (ERD) were examined with t-test. ERS were observed in α-band on the left-hemisphere in case of “with speech imagery” for latency of 500-1500 ms and the significant differences (p<0.05) were shown in the left-hemisphere and occipital-region. It is suggested the useful information of selecting electrode positions to detect EEG frequency components for judgment of “with/without speech imagery” in the intention. In addition, an examination to localize electrode was conducted. As a result, it is suggested that averaged RMS value for each frequency component gives useful information even when localized to 9 electrodes.