Read the following if you require more details.
Using the OfflineAnalysis tool I'm getting nice 1/f spectra during imagery and similar spectra during rest with the exception of a nice peak around 14Hz. This also yields great rsq values around that frequency. See the attached figure. {5:C3, 6:Cz, 10: P3, 11: Pz}. I did not use any spatial filter. Based on this assessment I would use C3 @ 14Hz as my control signal.
I tried to simulate this result by using the bci2000chain tool using only
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TransmissionFilter|ARFilter
How should I normalize this feature for control?
A simple, non-adaptive, way to normalize would be to take the median value of C3 @ 14Hz as the offset and then scale by 1/variance. In my experience, spectral amplitude is not normally distributed so it seems like the cursor will not have equal speed on either side of the midline. I find that brain signals can be made a little more normal by taking the power in db (10*log10(amplitude^2)) but currently BCI2000 does not offer this option.
We can also use an adaptive normalizer http://www.bci2000.org/wiki/index.php/U ... Normalizer. This way the offset and gain are updated every trial based on some previous data. The problem with this is that the result of adaptive normalization isn't really the same as the result using OfflineAnalysis.
I repeated the bci2000 chain analysis using
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TransmissionFilter|ARFilter|LinearClassifier|Normalizer
If I had hours and hours of data instead of the 40 trials here, would the results converge?
Should cursor speed be 0 at the beginning of a trial (i.e., normalized to baseline)? Should we assume that there is some drift in the control signal that the subject will never have voluntary control over and therefore normalize the cursor speed to some previous amount of data? Or should the cursor speed always be some direct transformation of the current amplitude (or power) with the expectation that the subject will eventually learn to return the signal amplitude to baseline between trials?
Does the answer change if the goal is to induce plasticity vs to provide useful control?
Thank you for any insight.