Raw EEG plots

[timo.veldt]

I've created a few data files using BCI2000's:
- operator.exe
- gUSBamp.exe
- P300SignalProcessing.exe

And my own Application module, similar to StimulusPresentation.exe. However when I plot the averages of my targets (numbering 200) and non-targets (approximately 600) using matlab I get very weird scales.

My time axis runs from 0 up to 256, which is one second in samples. The voltage axis runs from -4000 up to 6000 across the different graphs. I was wondering what unit goes with this axis, since if it is nanovolts, things look considerably brighter than if it is anything else.

In matlab I've used load_bcidat(<filename>) and then used a script to use states.StimulusType and states.StimulusBegin to extract the data.
When plotting the entire signal (i.e. [signal, states, parameters] = load_bcidat(<filename>)) and then in the workspace window right-click signal and press "Plot all columns", I get approximately 9 minutes on the time axis and the voltage scale runs from -1.5*10^5 to 2*10^5.

So my question, what unit goes with the voltage scale???

[mellinger]

When using load_bcidat, specify the -calibrated option in order to obtain data calibrated into microvolts:

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[signal, states, parameters] = load_bcidat( 'filename', '-calibrated' );

Otherwise, you get data in raw units, which depend on the SignalType, SourceChGain, and SourceChOffset parameters.

--Juergen

[timo.veldt]

Thanks for the suggestion, but I'm running into problems:

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 [signal, states, parameters] = load_bcidat('testS001R03.dat', '-calibrated');

gives the following error

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??? Error using ==> load_bcidat
File "-calibrated" does not exist.

Error in ==> getStimWaveForms at 4
[signal, states, parameters] = load_bcidat('testS001R03.dat', '-calibrated');

How can use this?

[mellinger]

You must be using a very old version of load_bcidat. Please update to a current version of BCI2000.

To find out which mex file your Matlab installation is using, type

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which load_bcidat

from the Matlab prompt.
To find out which version the load_bcidat mex file is, type

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load_bcidat --version

--Juergen

[timo.veldt]

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which load_bcidat
mario\data_io\load_bcidat.dll

This is indeed an older version, but I couldnt find the newer MEX file which is compatible to my system (XP, SP3, Matlab R2007b), so I used this one instead. Could you give me a direction to a newer file, or how I should build/create one?

Thank you again!

[mellinger]

The BCI2000 binary distribution comes with compiled versions of all the BCI2000 mex files. These should be compatible with your version of Matlab as well.

A list of recent BCI2000 binary distributions is available at
http://www.bci2000.org/wiki/index.php/BCI2000_Binaries
The latest BCI2000 binary distribution may always be downloaded from
http://bci2000.org/downloads/bin/BCI2000Setup.exe

--Juergen