<div dir="ltr"><div><div>Thank you Makoto.<br></div><br></div>After playing a while and digging into some souce codes and tech notes, here are some of my experience. Hope they will be helpful to other (present and future) users:<br>
<br>++++++<br><span style="font:14px Helvetica">size(EEG.data) is independent from channel location information. One can have 128 channels in the data and have 132 channel information ( in which case 4 channels do not have actual data).</span><br>
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<span style="font:14px Helvetica">When exporting from net station as raw using waveform tools/file export with "export reference channel" (e.g. Cz), the raw file has reference channel data (flat line, zero) and location information.</span><br>
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<span style="font:14px Helvetica">When importing to eeglab, eeglab would delete empty data reference channel (reference channel location is retained: only mark that channel type as REF, the eeglab main window still shows reference as "unknown").</span><br>
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<span style="font:14px Helvetica">When eeglab shows the reference is "unknown", one can declare Cz as the reference channel. But this does not change the data themselves at all; it just changes the label.</span><br>
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<span style="font:12px Helvetica"><i> How to declare a channel as reference channel: (1) insert head model if necessary (2) you would have the channel location information for your reference channel from the head model (3) the reference channel is at the end of the channel list, it is not in the data array (4) set reference for channel indices, i.e. all channels. once set, in the main window you will see the reference changes to your specified channels</i></span><br>
<span style="font:14px Helvetica"><br>Re-reference to average: simply click "Tools | Re-reference | Computer average", leaving other boxes empty. EEGLAB uses V'i = (Vi-Vref) - sum(Vi-Vref)/number_of_electrodes, #electrodes = size(EEG.data) = 128 in my case. See the tech note here (</span><span style="font:14px Arial;color:rgb(15,0,238)"><u><a href="ftp://ftp.egi.com/pub/documentation/technotes/AverageReference.pdf">ftp://ftp.egi.com/pub/documentation/technotes/AverageReference.pdf</a></u></span><span style="font:14px Arial">)</span>
<br><br><span style="font:14px Helvetica">"retain old reference channels in data": say re-ref to E55, uncheck this box, E55 would disappear from the new dataset (it is simply a flat line). total #channels decreases by 1.</span><br>
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<span style="font:14px Helvetica">"Add current reference channel back to data": add the data of that channel back (in case of Cz, 0) and total #channels increases by 1. Computer based on the changed data (original data + 000...000 from Cz)and increased #channel (e.g. 129). Use EEG.data(1:8) to see the actual EEG data changes.</span>
<br>++++++<br></div><div class="gmail_extra"><br clear="all"><div><div dir="ltr"><div><span style="font-family:times new roman,serif">--<br>Jian Zhu, M.A.<br>Brain and Cognitive Sciences<br>Department of Psychology<br>Southern Illinois University Carbondale<br>
</span></div><span style="font-family:times new roman,serif">Web: <a href="http://zhupsy.com" target="_blank">http://zhupsy.com</a><br></span><div><span style="font-family:times new roman,serif"><br>We have two halves in the brain: left and right. Nothing is right in the left. Nothing is left in the right.</span></div>
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<br><br><div class="gmail_quote">On Mon, Jun 16, 2014 at 8:49 PM, Makoto Miyakoshi <span dir="ltr"><<a href="mailto:mmiyakoshi@ucsd.edu" target="_blank">mmiyakoshi@ucsd.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr">Dear Jerry,<div><br></div><div><div class="">> Should I include Cz when computing average?<br><div class="gmail_extra"><br></div></div><div class="gmail_extra">No.</div><div class=""><div class="gmail_extra">
<br></div><div class="gmail_extra">
> I simply click "Tools | Re-reference | Computer average", leaving other boxes empty.<br></div><div class="gmail_extra"><br></div></div><div class="gmail_extra">Yes, that's the way to go.</div><div class="gmail_extra">
<br></div><div class="gmail_extra">If you want to recover Cz for any reason, do it after above steps. EEGLAB allows users to do channel interpolation. In doing so, you need to prepare a dataset that has Cz though.</div><div class="gmail_extra">
<br></div><div class="gmail_extra">Makoto</div><div class="gmail_extra"><br><div class="gmail_quote"><div><div class="h5">On Mon, Jun 16, 2014 at 4:59 PM, Jerry Zhu <span dir="ltr"><<a href="mailto:jerryzhu@siu.edu" target="_blank">jerryzhu@siu.edu</a>></span> wrote:<br>
</div></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div><div class="h5"><div dir="ltr"><div><div>
<div><div>Hi all,<br></div>My 128-channel data use Cz as the reference channel during collection. I wanna re-reference to average. Should I include Cz when computing average?<br>
<br></div>If not, I simply click "Tools | Re-reference | Computer average", leaving other boxes empty. After that I got a file with 128 channels.<br>
<br></div>If yes, I declare Cz as the reference through the GUI "Edit | Channel location | Set reference". Then in "Tools | Re-reference | Computer average" I also "add current reference channel back to data". After that I got a file with 129 channels (including the Cz). <br>
(a side-note, I also found that I can skip the step of declaring Cz as reference and directly add Cz back to data in "Tools | Re-reference | Computer average". So is setting a reference channel necessary to begin with?)<br>
<br></div>Which way is "correct" or "preferred"? <br><div><div><div><div><div><div><div><div dir="ltr"><div><span style="font-family:'times new roman',serif">--<br>Jian Zhu, M.A.<br>Brain and Cognitive Sciences<br>
Department of Psychology<br>Southern Illinois University Carbondale<br></span></div><span style="font-family:'times new roman',serif">Web: <a href="http://zhupsy.com" target="_blank">http://zhupsy.com</a><br></span><div>
<span style="font-family:'times new roman',serif"><br>
We have two halves in the brain: left and right. Nothing is right in the left. Nothing is left in the right.</span></div></div></div>
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-- <br><div dir="ltr">Makoto Miyakoshi<br>Swartz Center for Computational Neuroscience<br>Institute for Neural Computation, University of California San Diego<br></div>
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