<div dir="ltr"><div class="gmail_default" style="color:#333399">Yes rereference before ICA as suggested by Jason. That's what i;ve been doing too most recently.</div><div class="gmail_default" style="color:#333399">There's also been several similar discussions or messages on the list over the past few years that you can review, including notes from Jason. You can google the eeglablist to find those.</div></div><div class="gmail_extra"><br><div class="gmail_quote">On Mon, Jan 11, 2016 at 9:16 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 Ben,<div><br></div><div><span class=""><div>> 1) Given that BioSemi data is collected essentially "reference-free", is it OK to perform ICA before re-referencing?</div><div><br></div></span><div>That's my understanding, since common-mode noise you reject by re-referencing is basically a linear operation which ICA should not be affected. HOWEVER, if your common-mode noise is huge, I recommend you average-reference before ICA--it may help (or not, I don't know but should not hurt).</div><span class=""><div><br></div><div>> 2) After using ICA to remove eye blink components and project back to sensor space, can I re-reference the cleaned data directly? Or do I need to first re-reference the original data AND the unmixing matrix from the ICA before removing the bad components?</div></span></div><div><br></div><div>I discussed it with my super smart colleague Jason Palmer. He strongly recommended you average-reference BEFORE ICA. The reason for it is that it realizes zero-sum assumption that dipole model has... which sounded quite trivial to me but again it does not hurt! If you re-reference before ICA you want to explicitly adjust the rank by pca option or you want to reject one channel (I always recommend this solution since simple).</div><div><br></div><div>Makoto</div><div class="gmail_extra"><br><div class="gmail_quote"><div><div class="h5">On Thu, Jan 7, 2016 at 1:04 PM, Benjamin Skerritt-Davis <span dir="ltr"><<a href="mailto:bsd@jhu.edu" target="_blank">bsd@jhu.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">Hi everyone,<div><br></div><div>I need some advice on cleaning BioSemi EEG data using ICA. I have data with 38 channels, and I would like to be able to analyze the data using different re-reference channels after ICA cleaning (e.g., linked mastoids, nose). My intuition is to run ICA on all 38 channels (before re-referencing) so the data is full rank, project out any "bad" components, then re-reference the cleaned data. A couple of questions:</div><div><br></div><div>1) Given that BioSemi data is collected essentially "reference-free", is it OK to perform ICA before re-referencing?</div><div><br></div><div>2) After using ICA to remove eye blink components and project back to sensor space, can I re-reference the cleaned data directly? Or do I need to first re-reference the original data AND the unmixing matrix from the ICA before removing the bad components? </div><div><br></div><div><br></div><div>I've found conflicting answers to similar questions online, so I'm hoping for consensus this time around. =)</div><div><br></div><div>Thanks for the help,</div><div>-Ben</div></div>
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