Filtering scope

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Module information
Modules BESA Research
Version 6.1 or higher

Overview

In EEG/MEG data analysis frequency filtering is one of the most basic and at the same time important operations. In BESA Research filtering is implemented as a linear operation so it is interchangeable in the processing pipeline - it can be changed at every processing step in almost all situations. There are however some moments that filtering cannot be applied in a linear manner - i.e. averaging. In general, we recommend not to apply filtering during such types of operations (apart from high pass to reduce drifts) as it can still be applied afterwards. You will be prompted by the application if you encounter this type of situation in data analysis:

Filter notification.jpg

Also at some stages of the data processing, filtering is of major importance, therefore we made it more accessible and you can easily redefine it. Please have a look at the table below:

Filter type Review window Search Average View Averaged buffer FFT lienear corelation / regression Combine Conditions ERP Coherence Time Frequency plot
(single click)
TopViewer Source Analysis
Low/High pass Main Main / can be redefine to default values(2-35Hz) as used during buffer creation Main Main None ERP ERP Main Main SA
Notch Main Main / can be redefine to default values(2-35Hz) as used during buffer creation Main Main None Main Main Main Main Main
Bandpass Main Main / can be redefine to default values(2-35Hz) as used during buffer creation Main Main None ERP ERP Main Main Main
Polygraphic Main* Main* / can be redefine to default values(2-35Hz) as used during buffer creation Main* Main* None Main* Main* Main* Main* n.a.
artifact correction Main Main / can be redefine to default values(2-35Hz) as used during buffer creation Main Main Main ERP ERP Main Main Main/SA

Main settings

The main setting for artifact correction can be set using EdF or menu entry Filters/Edit Filter Settings...

Filter main.jpg

Specific ERP settings

The ERP filter settings can be set during paradigm definition. Note that there are two different settings - for artifact scan and for averaging.

Filter ERP.jpg

Specific Source Analysis settings

For source analysis (SA), if you press ESI/MSI button on the toolbar ribbon Main filter settings will be used. Filters for SA can be set during sending a block of data to Source Analysis (right-click on the highlighted block and select Source Analysis).

Filter SA.jpg

In case of enabled artifact correction, you will be prompted just before averaging if you want to average artifact corrected data or not. The detailed description of difference in both approaches can be found here

Notch filter

Note that because of its generic nature - power line artifact removal - the notch filter is treated differently. The notch filter value populates from Main setting to all subsequent applications.

Bandpass filter

The bandpass filter is complementary to the high/low pass filter combination. For convenience, it is treated differently (it also has different filter characteristics) and also populates to all subsequent applications from Main setting.

Polygraphic filter

Polygraphic channels are filtered using Main settings. Note that there are additional settings that can be applied to the polygraphic filter accessible via Filters/Polygraphic/Additional Chans...

Filter poly.jpg

See also