TAILIEUCHUNG - Biomedical Engineering 2012 Part 5

Tham khảo tài liệu 'biomedical engineering 2012 part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 152 Biomedical Engineering Fig. 4. Example showing a high-amplitude artefact Here the test is computed on the raw EEG data every 10s. A moving window is compared to a fixed reference window as shown in fig. 3. The reference variance is calculated on an artefact-free time window lasting one minute chosen at the beginning of the recording . Then a moving window of 10s is compared to this reference every 10s. The threshold .art is empirically chosen and discussed in section 3. The goal is to detect the artefact not to reject it. As the system is working on a minimal number of EEG channels it is not possible to recover lost EEG information of the artefact since missing information cannot be found somewhere else. Nevertheless detecting the occurrence of an artefact provides information on the signal quality whenever an artefact is detected the concomitant relative power extracted from EEG should not be used to evaluate drowsiness. Method relevance The whole algorithm can be applied on-line. However the sliding window of 10s used for median filtering induces a delay of 5s and the sliding window of 30s used for the MCT induces a delay of 15s. The artefact detection is computed in parallel with a sliding window of 10s which induces a delay of 5s. So the decision provided by the algorithm is delayed by 20s from the signals recording. This latency in the decision will be taken into account when comparing the results to the expert s decisions. The general purpose of this algorithm is the detection of drowsiness. The MCT detects a bursts which are indicators of drowsiness as seen in section 1. The reference is calculated on a fixed window chosen at the beginning of the signal supposing that the driver is completely awake when he starts driving. So the mean calculated on the moving window is compared to a wakefulness reference. If the bilateral test is higher than the threshold the driver is then considered as drowsy otherwise he is considered as awake. Fig. 6 shows how the

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