2d and 3d visualisation

[neptunier]

hi all,
i want to use the 2d and 3d visualisation as a feedback modality for neurofeedback, that means watching the amplitudes in real time. i connected just one channel at cz and was watching what was displayed. somehow, it did not make much sense. i could compare it with the output of the nfb software which was running at the same time. i was adjusting the bandpass frequencies for both programms the same and tried several simple dsp`s. somehow i do not understand the color spectrum, yellow meaning +, blue 0 and red -. if blue is zero, what does this zero stand for? the display was the other way arround than the amplitude. usually the whole head was red, when there was more activity on cz, cz remained red but the fringe turned yellow.
did i do anything wrong or which kind of settings and dsd`s would be necessary to wath amplitudes in real time?
thanks for your help,
michael

[fabien.lotte]

Dear Neptunier,

I don't know how the color spectrum scale works, but if you want to compare the signal band power between openvibe and another software for a single channel, it's probably better to use the simple signal display for that channel (after band-pass filtering, squaring and smoothing for instance). Indeed, if I am not wrong (dear OpenViBE developers, don't hesitate to correct me if I am wrong!), the 2D and 3D visualization tools are more dedicated to observe instantaneous spatial patterns, and probably won't make much sense if used with a single channel (the amplitude is indeed interpolated between the available channels).

I hope this helps,

Best regards,
Fabien

[lbonnet]

Hi,

I agree with Fabien, the 2d and 3d displays interpolate between the different channels.
For one channel signal, it's a bit irrelevant

For only one channel, it's more like you need a "level" representation. The signal display can do it, as you can see in the neurofeedback scenario with the beta level on Cz.

hope this helps
Laurent

[neptunier]

hi fabien and laurent,
thanks for your replies. i will try 2 channels and see what is happening. but still i am not sure what is visualized. it has to be amplitude i guess, processed in on or other way with dsp. so i dont understand why the spectrum goes from - over 0 to +.
what is the 0 then?
michael

[yrenard]

Hello everyone,

your are actually referring to bug #34

Forget the 0, the color scale is representing low values with blue color and high values with red color, no matter if 0 is between these two min / max values ; also, the data scale is refreshed for each input value to fit the color scale.

You should not use topography visualisation if you don't have a spatially relevant covering of the scalp anyway.

Hope this helps,
Regards,
Yann