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Dear FieldTrip community,<br>
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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>
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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.</div>
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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>
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hdr (1x1 struct)</div>
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label (62x1 cell)</div>
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time (1x1 cell)</div>
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trial (1x1 cell)</div>
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fsample - 500</div>
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sampleinfo [1, 366525]</div>
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cfg (1x1 struct)</div>
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<font face="Calibri, Arial, Helvetica, sans-serif">Here, <i>cfg</i> has <i>refchannel</i> =[ ] and
<i>refmethod</i> = 'avg'. <i>label </i> has total 62 entries which are: 1 to 61 (except 29), VEOG, and aux5.</font></div>
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<div style="background-color: rgb(255, 255, 255); color: rgb(0, 0, 0);"><font face="Calibri, Arial, Helvetica, sans-serif">A proc structure containing the preprocessing parameters has been given which includes
<i>trl</i>, <i>badchans</i>, <i>implicitref</i> as 29 and <i>refchannels</i> as 25 and 29.</font></div>
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<div style="background-color: rgb(255, 255, 255); color: rgb(0, 0, 0);"><font face="Calibri, Arial, Helvetica, sans-serif">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.</font></div>
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<div style="background-color: rgb(255, 255, 255); color: rgb(0, 0, 0);"><font face="Calibri, Arial, Helvetica, sans-serif">Then I use the following cfg for re-referencing:</font></div>
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<div style="background-color: rgb(255, 255, 255); color: rgb(0, 0, 0);"><font face="Calibri, Arial, Helvetica, sans-serif">cfg_reref.implicitref = '29';
<div>cfg_reref.reref = 'yes';</div>
cfg_reref.refchannel = proc.proc.refchannels;<br>
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<div style="background-color: rgb(255, 255, 255); color: rgb(0, 0, 0);"><font face="Calibri, Arial, Helvetica, sans-serif">rereferenced_data = ft_preprocessing(cfg_reref, repaired_data);<br>
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<div style="background-color: rgb(255, 255, 255); color: rgb(0, 0, 0);"><font face="Calibri, Arial, Helvetica, sans-serif">Now, the
<i>label</i> of rereferenced_data has 59 channels only.</font></div>
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</font></div>
<div style="background-color: rgb(255, 255, 255); color: rgb(0, 0, 0);"><font face="Calibri, Arial, Helvetica, sans-serif">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>
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I am working with EEG for the first time. Any help would be highly appreciated.<br>
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Thanking you,<br>
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Sincerely,<br>
Akshi<br>
IIIT-Bangalore, India</font></div>
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