<div dir="ltr">Dear Fabio,<div><br></div><div><div style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial">> I have a (probably naive) question regarding ICA.<br></div><div><br></div>I'll give you my naive answers, not intentionally but due to my limitations. Follow them at your own risk.<br class="gmail-Apple-interchange-newline"><br></div><div><div style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial">> - whether I should or not choose the whole 128 channel set for running ICA</div><div style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial"><br></div><div style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial">Yes, unless your data is too short for that. Remember, (number of channels)^2 x 30 data points at 256 Hz sampling rate is a rule of thumb for running ICA.</div><div style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial"><br></div><div style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial">> - consequently, how I should <i>a priori</i> decide which channels to consider for ICA and which not.<br></div><br></div><div>You can determine a priori which anatomical regions you are going to analyze. Then, if ICA gives you the '(stationary) effective source locations' that overlap /are close enough to those pre-selected regions, pick them up for the final analysis.</div><div><br></div><div>ICA is a hypothesis-free approach, but that does not mean you cannot have a hypothesis.</div><div>You might enjoy reading the classic discussion between ICA pioneers and Karl Friston about how ICA could be used in neuroscience data analysis.</div><div><div>Friston KJ. <span style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">Modes or models: a critique on independent component analysis for fMRI. </span>Trends Cogn Sci.  1998. Oct 01; 2(10) 373-375</div></div><div><br></div><div><span style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">> The recordings are ~2 minutes long and the sampling rate is 1000 Hz.</span></div><div><span style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><br></span></div><div><span style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">If you have only 2 min, you definitely cannot perform >100ch ICA.</span></div><div><span style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">sqrt(250 Hz x 120 sec / 30) is about 31, so you want to use 'pca' option to perform dimension reduction to obtain 31 ICs.</span></div><div><span style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><br></span></div><div><span style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">> I would like to keep as many channels as possible during pre-processing, and afterwards discard the ones I realize are not useful to my analysis - if this approach seems reasonable.</span><br></div><div><br></div><div>Record longer. 2-min EEG is too short if you want to use ICA.</div><div><br></div><div>Makoto</div><br><div class="gmail_quote"><div dir="ltr">On Thu, Jul 19, 2018 at 3:26 AM Giatsidis, Fabio <<a href="mailto:fabio_giatsidis@brown.edu">fabio_giatsidis@brown.edu</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr">

<div style="font-size:small;text-decoration-style:initial;text-decoration-color:initial">Hello EEGLAB list,</div><div style="font-size:small;text-decoration-style:initial;text-decoration-color:initial"><br></div><div style="font-size:small;text-decoration-style:initial;text-decoration-color:initial">I have a (probably naive) question regarding ICA.<br></div><div style="font-size:small;text-decoration-style:initial;text-decoration-color:initial">I have been using an <span style="font-size:12.8px;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">EGI 128-channel system to record resting states. I have been reading a bit about ICA, but </span>it is still not clear to me:</div><div style="font-size:small;text-decoration-style:initial;text-decoration-color:initial">- whether I should or not choose the whole 128 channel set for running ICA, and</div><div style="font-size:small;text-decoration-style:initial;text-decoration-color:initial">- consequently, how I should <i>a priori</i> decide which channels to consider for ICA and which not.</div><div style="font-size:small;text-decoration-style:initial;text-decoration-color:initial"><br></div><div style="font-size:small;text-decoration-style:initial;text-decoration-color:initial">The recordings are ~2 minutes long and the sampling rate is 1000 Hz. I would like to keep as many channels as possible during pre-processing, and afterwards discard the ones I realize are not useful to my analysis - if this approach seems reasonable.</div><div style="font-size:small;text-decoration-style:initial;text-decoration-color:initial"><br></div><div style="font-size:small;text-decoration-style:initial;text-decoration-color:initial">Also:</div><div style="font-size:small;text-decoration-style:initial;text-decoration-color:initial">- if as a very first step I delete some clearly bad channels and then interpolate them to repopulate the original channel set, is it legit to include such interpolated channels during ICA?</div><div style="font-size:small;text-decoration-style:initial;text-decoration-color:initial"><br></div><div style="font-size:small;text-decoration-style:initial;text-decoration-color:initial">Thank you very much!</div><div style="font-size:small;text-decoration-style:initial;text-decoration-color:initial">Best,</div><div style="font-size:small;text-decoration-style:initial;text-decoration-color:initial">-Fabio</div><div style="font-size:small;text-decoration-style:initial;text-decoration-color:initial"><br></div><div style="font-size:small;text-decoration-style:initial;text-decoration-color:initial">--------------------------------</div><div style="font-size:small;text-decoration-style:initial;text-decoration-color:initial"><i>Fabio Giatsidis, M.D.</i></div><div style="font-size:small;text-decoration-style:initial;text-decoration-color:initial">Resident in Neurology - University of Rome "Tor Vergata" - Rome, Italy</div><div style="font-size:small;text-decoration-style:initial;text-decoration-color:initial">Post-doctoral research fellow - Brown University - Providence, RI, USA</div></div>
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