Biosemi cursor task and laplacian questions

Forum for discussion on different signal processing algorithms
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Joined: 20 Jun 2011, 11:06

Biosemi cursor task and laplacian questions

Post by dkiviat » 26 Jul 2011, 19:26

I'm using a biosemi 128 electrode eeg, and I have two questions about implementation (one specific to biosemi, one a general signal processing question. When I run experiments, the online signal display usually only displays signal for around 4 channels, even though im collecting 128 channels worth of data. Im assuming this is because I set offset=0, though im not sure. If this is the case, I dont think its that important as far as analysis goes, but it would ease my peace of mind if I could actually see the channels as theyre being recorded, or at the very least know this is the reason theyre not showing up. Is there any easy way to quickly collect and export offsets for 128 channels from labview to biosemi.

Also since Im using a relatively high density array, if I see relevant activity in neighboring electrodes should I give them both positive coefficients in the classifier matrix (say .5 and .5) and then subtract away the six or so neighboring electrodes? And do the row names need to match channel names (eg A1 A2 A3 A4 A5 A6 etc, or will simple numbering (1 2 3 4 5 6 7...) be sufficient?

Posts: 1098
Joined: 12 Feb 2003, 11:06

Re: Biosemi cursor task and laplacian questions

Post by mellinger » 03 Aug 2011, 08:01

I'm not sure about what you are asking regarding the online signal display. By default, it displays up to 16 channels. More channels may be displayed by selecting "More channels" from the context menu.
When you suspect wrong offsets to be the problem, try a highpass filter in the visualization display (also available from the context menu).

For more information about visualization windows, see ... on_Windows

Unfortunately, I'm unfamiliar with the Biosemi amplifier, so I cannot help you regarding channel offsets. Typically, all channels have the same offset, so you may use, e.g. Matlab to print 128 values in a row, and paste-and-copy this into the Operator interface.

In your last question, I guess you are referring to the SpatialFilter matrix rather than the classifier matrix. There, you may use numbers as well as channel names, but beware that numbers will change their meanings depending on the TransmitChList parameter. When using channel names, you will be on the safe side.



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