Tham khảo tài liệu 'new developments in biomedical engineering 2011 part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 32 New Developments in Biomedical Engineering val of 1s 85 of the stimuli at 800Hz and randomly presented 15 deviant tones at 560Hz. The subject was sitting in a chair and was asked to press a button every time he heard the deviant target tone. The sampling rate of the EEG was 500 Hz. From the recordings channel Cz was selected for analysis after bandpass filtering in the range 1-40Hz. Average responses from the two conditions are shown in Figure 2 Section 2 . For investigation of the single trial variability of the P300 peak EEG epochs from -100 ms to 600 ms relative to the stimulus onset of each deviant stimulus were here used. The model was designed as in section but now for the slower P300 wave the selection fc 10Hz was made. The application of the empirical rule 27 gave in this case k 15. Kalman smoother estimates were computed with the selection 022 9 with respect to the expected faster variability of the potential. In Figure 5 I there are presented the EP measurements in the original stimulus order trial-bytrial . In the same figure II the obtained estimates based on the measurements I are shown. Clearly in the estimates the dynamic variability of the P300 peak potential is revealed suggesting that it cannot be considered as occurring at fixed latency from the stimuli presentation. At the same image II the estimated latency is also plotted as a function of the consecutive trial t. The latency of the peak was estimated from the Kalman smoother estimates based on the maximum value within the time interval 250-370ms after the presentation of the stimuli. The estimated time-varying latency of the P300 peak was then used to order the single-trial measurements. The sorted single-trials condition-by-condition are shown at Figure 5 III . The shorted latency estimates are plotted again over the image plot. This plot clearly demonstrates that the latency estimates obtained with Kalman smoother are of acceptable accuracy. Finally the algorithm was also applied to .
