Max Value of Mu Power

[verasen]

I've managed to attain the mu power in my application. I ran it yesterday and what I don't understand is how do you know the max value of the mu power? I hear it is 32767 but when we ran a subject the number rarely went above a 1000. In fact, most of the time it's under 400. To move the cursor, you need to set a midpoint which allows the cursor to move left or right. The midpoint is determined by Max/2. But I don't know max in this case. It can be different for different subjects right? So how do you go about doing this?

Thanks,
Umang

[gschalk]

Hi,

This is a good question. In BCI2000, the concept is that a properly configured Signal Processing module will scale the values (and subtract an "appropriate" offset) so that the output of signal processing (and thus, the input into the User Application) is always normalized to be between +-32767. In addition, if adaptation is turned on, it will also adapt the offset and gain so as to track slow changes in signal dynamics.

If you see values in the Application that are scaled very differently (e.g., are between 0 and 400), then Signal Processing is not configured correctly. The values to check are UD_A (up-down offset), UD_B (gain) in Filtering, InterceptControl and PixelsPerSecond (in Statistics) (these settings will ask the controller in signal processing to adaptively modify UD_A and UD_B).

If you have any further questions, please just post them. In any event, DO NOT IMPLEMENT A SCALING/OFFSET REMOVAL SCHEME IN THE APPLICATION!! This is agains the principle of independence set forth in the BCI2000 article. (You should read the draft on bci2000.org for a good conceptual overview).

Gerv