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PostPosted: Wed Oct 10, 2018 8:26 am 
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Joined: Tue Mar 13, 2018 12:39 pm
Posts: 12
Dear all, recently I've tried to use the continuous wavelet analysis box as a feature generator for motor imagery BCI scenarios. My use case was similar to using FFT for that purposes, I did not really care about the timing of the features (relevant pieces of the EEG signal are selected using the 'Stimulation based epoching' box). For that purpose, I put together a simple python box that aims to re-arrange the CWT time-frequency output into chronologically sorted frequency bins (generated by the CWT).

You can find the box here: https://github.com/xskola/notes-on-openvibe. It requires one setting, 'Number of frequencies' (set it to correspond to your CWT setting) and can handle arbitrary number of channels. Nevertheless, the code is very simple and probably will require some adjustments for future utility.


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PostPosted: Fri Oct 19, 2018 8:49 am 
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Joined: Tue Dec 04, 2012 3:53 pm
Posts: 762
Location: INRIA Rennes, FRANCE
Hi Xskola, thanks for the idea and the link! It'd be interesting to know if you got improved results from it in comparison to some baseline features (which?).

Cheers,
Jussi


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PostPosted: Wed Nov 07, 2018 2:25 pm 
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Joined: Tue Mar 13, 2018 12:39 pm
Posts: 12
I actually run into some problems while trying to use this box in practice and I would like to ask you for your opininon on this.

I have an MI scenario with feature extraction using CWT + the mentioned python box, nothing really special going on there. I can sucessfully train the classifier (both on Linux and Windows) and I can also start the online scenario on Linux.

However, if I try to use this as online scenario on Windows, I run into a weird lagging issue. Basically, the time in designer starts having regular lags each second, related to the length of chunk in Time based epoching. With 1s epochs spaced 0.25s apart, I can still run the scenario, but I get past the realtime. With shorter epoch spacing, the scenario hangs after the first second. With 0.25s epochs 0.25 apart, the scenario runs fine in the beginning, but after a minute or so, it stops and freezes openvibe completely.

Also it is strange that this happens only if I "read" the data from classifier processor using matrix display or TCP writer with connected other end (scenario runs fine when TCP box is connected but client is not connected to the stream, or when there is no connection from classifier processor output). The lagging is also less prominent (can handle larger epochs/shorter intervals) when I use CSV writer to gather classifier results (caching?).

Number of frequencies in CWT nor clock frequency in Python box influence this issue.

I would be happy for any pointers how to get around this issue!

Many thanks,
Filip


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PostPosted: Thu Nov 08, 2018 10:32 am 
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Joined: Tue Mar 13, 2018 12:39 pm
Posts: 12
Correction: the issue is present on Linux (Debian) as well, just the epoch intervals can be multiple times lower (4-16x, depending on whether acquisition server or generic stream reader is used) to show this issue.

My thought was this is happening due to decomposition of 3- to 2-dimensional matrix in data from CWT, and too many chunks being inserted to the data stream, but limiting CWT output to just 1 frequency don't really change properties of the lagging.

Is it maybe just because of performance limitations? I can see Openvibe fully using one core on my CPU. It would still be strange that OV performance is that different on different OSes (on the same computer).


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