[FieldTrip] Frequency spectrum of virtual sensors differs from input data spectrum

Herfurth, Kirsten Kirsten.Herfurth at uk-erlangen.de
Thu Dec 20 12:30:56 CET 2018

Dear list members,

I would like to feed machine learning algorithms with virtual sensor data of different frequency bands as well as broad bands (e.g. 1-45Hz, beta-band etc) and would appreciate your help with some issues concerning the filtering of the data. In order to obtain virtual sensors, I compute lcmv beamformer with bandpass filtered averaged sensor data (e.g. filtered in beta band). After obtaining the spatial filter, I multiply the weights with the single trials filtered in beta band.
When checking the frequency spectrum of the beta band filtered average sensor data, the spectrum looks all right (see attached picture "mean sensor data betaband.png). However, when checking the frequency spectrum of the virtual sensors, the spectrum does not show signal in beta band, but shows a spectrum between 1 and 120 Hz, while signal seems to be missing around 20 Hz (see the other attached picture).

I checked all analyzing steps and found that the data covariance matrix already presents a similar frequency spectrum as the virtual sensors. I know too little to understand this issue and would appreciate it if anyone could help me here. Would it make more sense to filter only the virtual sensors, with no filtering at all beforehand?

Thanks for your help in advance, best regards,


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.science.ru.nl/pipermail/fieldtrip/attachments/20181220/e13c9d09/attachment-0001.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: freq_spectrum_avg_virtual_sensors_bp13-25Hz.png
Type: image/png
Size: 42150 bytes
Desc: freq_spectrum_avg_virtual_sensors_bp13-25Hz.png
URL: <http://mailman.science.ru.nl/pipermail/fieldtrip/attachments/20181220/e13c9d09/attachment-0002.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: mean_sensor_data_betaband.png
Type: image/png
Size: 25752 bytes
Desc: mean_sensor_data_betaband.png
URL: <http://mailman.science.ru.nl/pipermail/fieldtrip/attachments/20181220/e13c9d09/attachment-0003.png>

More information about the fieldtrip mailing list