Unable to import the data with correct time

sidhsu · October 18, 2022, 2:27am

Hi, I had a problem about importing data. My data record for 90 seconds but when I use EEGLAB data(.set) import into brainstorm, the data file only exist 90 mini-seconds.
Can someone help me understand what is happenning?
Thank you!
Sid Hsu

Francois · October 18, 2022, 8:56am

The problem is the sampling frequency (sfreq) set to 1000000Hz.
Other than that, the data in the file is consistent: 91760 samples at 1000000Hz = 0.09176 seconds.

The sampling frequency is computed in the import function as:

sFile.prop.sfreq = 1 ./ (hdr.Time(2) - hdr.Time(1));

See code:

github.com

brainstorm-tools/brainstorm3/blob/master/toolbox/io/in_fopen_eeglab.m#L300

      
        
            % Initialize returned file structure                    
            sFile = db_template('sfile');                     
            % Add information read from header
            sFile.filename   = DataFile;
            sFile.fid        = [];  
            sFile.format     = 'EEG-EEGLAB';
            sFile.device     = 'EEGLAB';
            sFile.byteorder  = 'l';
            % Properties of the recordings
            sFile.prop.times = [hdr.Time(1), hdr.Time(end)];
            sFile.prop.sfreq = 1 ./ (hdr.Time(2) - hdr.Time(1));
            sFile.prop.nAvg  = 1;
            sFile.header = hdr;
            % Channel file
            if ImportOptions.DisplayMessages
                isFixUnits = [];
            elseif (ImportOptions.ChannelAlign >= 1)
                isFixUnits = 1;
            else
                isFixUnits = 0;
            end

Why do you have the first two time samples in the file that are only 1e-6 seconds apart?
Is there some time issue in your original file?
What does it look like in EEGLAB?
What was the original file format (before importing it into EEGLAB)?
What does it look like if you load this original file directly into Brainstorm?

sidhsu · October 29, 2022, 3:16am

Thanks for your response. Our original files is (.Poly5) and this files was not included in the brainstrom menu. When I used ASCII format to read the data, it would cost a lot of time and couldn't read it, so I used the Matlab code to change this file (.Poly 5) into EEGlab files (.set). In EEGlab, the sampling frequency set to 1000 Hz, so I didn't know why the sampling frequency would turn into 1000000Hz in brainstorm. Is there any method could change the sampling frequency in brainstorm?
Thank you!
Sid Hsu

Francois · October 31, 2022, 8:15am

I probably have to fix something in the EEGLAB importer.

Can you please share a short example dataset?
Upload the file somewhere (e.g. google drive, onedrive, dropbox...) and post the download link here.
Thanks

sidhsu · October 31, 2022, 4:19pm

Thanks for your response. This is our EEGLAB dataset.
https://drive.google.com/drive/folders/11aCYNrcRFYZPW5S2Y3c9HDXdByfyRLgU?usp=sharing

Francois · November 2, 2022, 9:58am

Thank you for the example data.
The bug is now fixed: Bugfix: Import EEGLAB: Disabled the use of field "times" (unreliable … · brainstorm-tools/brainstorm3@f585d88 · GitHub
Update Brainstorm and try importing your file again.

sidhsu · November 6, 2022, 3:20pm

Thanks for your helping. It works perfectly.