To view the EEG, we use the program Net Station on the Mac. If an electrode suddenly gets bad, or the subject blinks a lot with his/her eyes, you can see this in the EEG. To view the EEG, do the following:
Click on the 'panels' tab in the top of the screen, and select 'dense waveform display'. Figure 1 The Panels menu (left) and the dense waveform display (right, without the EEG)
The EEG traces are shown best if you filter them: go to 'panels' again, and click 'digital filter controls'. Here you can set the high-pass, low-pass and notch filters, which will filter the signal that you see. This will NOT filter the signal that is saved or sent to BCI2000. Filtering is done in BCI2000 or off-line in NBT.
- Notch filter: filters out the 50 or 60 Hz signal coming from the electricity grid.
- High pass: keeps only frequencies above this value.
- Low pass: keeps only frequencies below this value.
Check the box for high-pass filter and set the slider to 1 Hz, check the box for the low-pass filter and set the slider to 45 Hz. Activate the filter by clicking the 'ON' button. A frequency range of 1-45 Hz is convenient, because it takes care of the 50 Hz noise from the grid (so you don't have to set the notch filter). Moreover, most information in the EEG is contained in this frequency range, because the amplitude of the EEG tends to become smaller the higher the frequency.
Organizing the EEG traces according to the 10-20 system gives you a better overview of the channels than displaying the default 128 or 256 channels. To do this, go to 'panels', click 'bipolar montage editor', and select '10-20' in the window that pops up. You can close this window.
If you have a prefixed time to record EEG, you can set a timer. Go to 'panels', and click 'Waveform Recorder Controls'. Set the 'Timed Record' to the preferred time. Do not use the number pad! Netstation will crash due to a bug.