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Bug 2869 - Change of data on EOG
| Status | CLOSED FIXED |
| Reported | 2015-03-16 19:37:00 +0100 |
| Modified | 2019-08-10 12:30:43 +0200 |
| Product: | FieldTrip |
| Component: | preproc |
| Version: | unspecified |
| Hardware: | PC |
| Operating System: | Windows |
| Importance: | P5 normal |
| Assigned to: | |
| URL: | |
| Tags: | |
| Depends on: | |
| Blocks: | |
| See also: |
Ekaterina - 2015-03-16 19:37:10 +0100
Why are the signals from '-HEOG1','-HEOG2','-IO','-65' channels change after average referencing, which excludes all non-EEG channels? cfg=[]; cfg.reref = 'yes' ; cfg.refchannel = {'all','-HEOG1','-HEOG2','-IO','-65'}; data_out = ft_preprocessing(cfg,data_for_reref); Best regards, Ekaterina
Ekaterina - 2015-03-16 19:49:23 +0100
Created attachment 708 data for prerocessing
Jim Herring - 2015-03-16 20:07:36 +0100
Dear Ekaterina, If I am not mistaken cfg.refchannel only specifies the channels that are supposed to be the reference. Cfg.channel specifies to which channels the rereferencing should be applied. In your example you are calculating the average reference over all channels except for the ones you excluded and applying the new referencing scheme to all channels.
Robert Oostenveld - 2015-03-16 21:08:40 +0100
Jim is correct.
Ekaterina - 2015-03-17 10:50:17 +0100
This means that if I want to use one matrix for EEG and EOG data and make reference, first I need to divide and then combine the data (because if I define the options cfg.channel and cfg.refchannel I will get on the output only EEG channels)
Robert Oostenveld - 2015-03-17 13:27:08 +0100
(In reply to Ekaterina from comment #4) yes, that is also how it is explained on for example http://www.fieldtriptoolbox.org/tutorial/eeg_preprocessing_erp#extracting_the_eog_signals and http://www.fieldtriptoolbox.org/tutorial/natmeg/preprocessing#combining_meg_and_eeg
Ekaterina - 2015-03-17 14:38:49 +0100
Robert, thank you very much for your answer Sorry, I have another question You can ask one more question about this link http://www.fieldtriptoolbox.org/tutorial/eeg_preprocessing_erp#extracting_the_eog_signals % only keep all non-EOG channels cfg = []; cfg.channel = setdiff(1:60, [53, 57, 25]); % you can use either strings or numbers as selection data = ft_selectdata(cfg, data); Why do you exclude [53, 57, 25], is it not the EEG channels? Maybe you need to exclude only 'LEOG'
Ekaterina - 2015-03-17 14:53:24 +0100
Sorry, I wanted to write this in Comment 6: Can I ask one more question about this link?
Robert Oostenveld - 2015-03-17 21:43:59 +0100
(In reply to Ekaterina from comment #7) I think that Irina (who wrote the tutorial) did this because she does not like to include these two very low channels close to the eyes in the subsequent EEG analysis. But that choice is up to you. The tutorial just shows one way that it can be done.