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Dear community,<br>
<br>
On closer inspection, I found out that there were some discrepancies between the neighbourplot I was getting using the layout I had and the ideal neighbourplot. This led me to prepare my own layout by plotting electrode positions manually and the issue is now
resolved.<br>
<br>
Thanks and regards,<br>
Akshi</div>
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Message: 1<br>
Date: Wed, 7 Oct 2020 11:55:32 +0000<br>
From: IMT2016025 Akshi <Akshi.025@iiitb.org><br>
To: "fieldtrip@science.ru.nl" <fieldtrip@science.ru.nl><br>
Subject: [FieldTrip] Decrease in channels after re-referencing<br>
Message-ID:<br>
<TY2PR0101MB2397534DBF972F9FEC8F7394B00A0@TY2PR0101MB2397.apcprd01.prod.exchangelabs.com><br>
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Dear FieldTrip community,<br>
<br>
I am Akshi, a fifth-year student of Integrated Master's (B.Tech + M.Tech) in Computer Science at IIIT-Bangalore, India. I am interested in understanding how brain processes language using EEG data.<br>
<br>
I would like to begin by expressing my gratitude to everyone for maintaining this awesome resource which is of great help to both newcomers and experts alike.<br>
<br>
I am using a dataset for which 61 actively-amplified electrodes and one ground electrode were used according to Easycap M10 layout. I have some concerns regarding the preprocessing steps I'm taking. I shall be extremely grateful to get any comment and advice
on this.<br>
<br>
The raw data has the following structure:<br>
hdr (1x1 struct)<br>
label (62x1 cell)<br>
time (1x1 cell)<br>
trial (1x1 cell)<br>
fsample - 500<br>
sampleinfo [1, 366525]<br>
cfg (1x1 struct)<br>
<br>
Here, cfg has refchannel =[ ] and refmethod = 'avg'. label has total 62 entries which are: 1 to 61 (except 29), VEOG, and aux5.<br>
<br>
A proc structure containing the preprocessing parameters has been given which includes trl, badchans, implicitref as 29 and refchannels as 25 and 29.<br>
<br>
I have used ft_redefinetrial to get epoched data followed by ft_preprocess to apply hpfilter, followed by ft_channelrepair to fill values for bad channels (here I added 29 as the missing channel). The data until now has 61 channels.<br>
<br>
Then I use the following cfg for re-referencing:<br>
<br>
cfg_reref.implicitref = '29';<br>
cfg_reref.reref = 'yes';<br>
cfg_reref.refchannel = proc.proc.refchannels;<br>
<br>
rereferenced_data = ft_preprocessing(cfg_reref, repaired_data);<br>
<br>
Now, the label of rereferenced_data has 59 channels only.<br>
<br>
Could someone please tell why this is happening and if the preprocessing steps are in the right order? I can give link to raw data, proc file and my script if needed.<br>
<br>
I am working with EEG for the first time. Any help would be highly appreciated.<br>
<br>
Thanking you,<br>
<br>
Sincerely,<br>
Akshi<br>
IIIT-Bangalore, India<br>
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