<div dir="ltr"><div dir="ltr"><div class="gmail_quote"><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="color:rgb(51,51,153)"><br>Hello Bert,<span class="gmail_default" style="color:rgb(51,51,153)"> notes below. </span> </div></div></blockquote><div><br></div><div class="gmail_default" style="color:rgb(51,51,153)">**************************************</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="color:rgb(51,51,153)">yes generally speaking that's what the rule of thumb for number of datapoints for ICA is about. Basically it has a big stomach, and in order to derive valid spatial ICA components, it needs enough "information". <span class="gmail_default" style="color:rgb(51,51,153)">When one does not have enough time-points, d</span>ownsampling helps, as well as, in some cases, reducing total number of channels. <span class="gmail_default" style="color:rgb(51,51,153)">However, I</span>'ve seen valid/neural/dipolar ICs from setups similar to the one you describe<span class="gmail_default" style="color:rgb(51,51,153)">, with only a few minutes of data and 64 or greater channels</span>. </div><div style="color:rgb(51,51,153)"><br></div><div style="color:rgb(51,51,153)">*<span class="gmail_default" style="color:rgb(51,51,153)">generally speaking, it is recommended to </span>retain only the relevant periods where participants are doing the intended task<span class="gmail_default" style="color:rgb(51,51,153)"> (and eliminate periods before, after, and between such tasks). A period where "nothing is happening" and "participant is just waiting" should be removed. Periods that are just a few seconds between trials, and which are artifact free, can remain. However, if you want to see for yourself, review your ICA solution when you A) leave in all your data (but without the artifact/noisy periods), and compare it to the ICA solution when having removed all the periods that are not-of-interest (where the participant is not engaged in a particular task you have required of them). Note that "resting" periods, for example, a few minutes of eyes closed resting, are considered "tasks".</span></div><div style="color:rgb(51,51,153)"><br></div><div style="color:rgb(51,51,153)">*make sure to have removed the "bad periods" so that ICA doesn't get confused by them, as per the eeglab tutorials (if you're new to ICA-EEG, look at results with and without such cleaning to get a feel for why basic cleaning is important for ICA).</div><div style="color:rgb(51,51,153)"><br></div><div style="color:rgb(51,51,153)">*<span class="gmail_default" style="color:rgb(51,51,153)">if you haven't had a chance to, </span>review the basic "kinds of valid/neural ICs" that can show up, as described in various recent articles you can find via Google Scholar from Makeig/Delorme/Artoni, and also in various articles about IC selection methods/plugins (SASICA, ADJUST, MARA, etc..)<span class="gmail_default" style="color:rgb(51,51,153)">. </span><span class="gmail_default"> also see </span>check out tutorial on IC<span class="gmail_default">A types</span><span class="gmail_default"> </span><span style="color:rgb(34,34,34)"><a href="https://labeling.ucsd.edu/tutorial">https://labeling.ucsd.edu/tutorial</a></span><span style="color:rgb(34,34,34)"> </span><span style="color:rgb(34,34,34)"> </span></div></div></blockquote><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="color:rgb(51,51,153)"><br></div><div style="color:rgb(51,51,153)">*run ICA anyway on a shorter period (you won't break anything) and see if you get interpretable and expected/normal neural ICs. <span class="gmail_default" style="color:rgb(51,51,153)">Note that m</span>any <span class="gmail_default" style="color:rgb(51,51,153)">existing </span>publications have used quite short periods that don't fit under this (ideal) rule about "enough timepoints"<span class="gmail_default" style="color:rgb(51,51,153)">. However, the validity of their ICs should be considered with caution.</span></div><div style="color:rgb(51,51,153)"><br></div><div style="color:rgb(51,51,153)">*google scholar articles that use ICA with short resting/continuous periods, or that use alternative techniques for source decomposition (e.g., variants of ICA, or even PCA -though PCA is not recommended by eeglab developers)</div><div style="color:rgb(51,51,153)"><br></div><div style="color:rgb(51,51,153)">*google eeglablist + your topic for previous eeglablist comments related to <span class="gmail_default" style="color:rgb(51,51,153)">your topics</span></div><div style="color:rgb(51,51,153)"><br></div><div style="color:rgb(51,51,153)">*<span class="gmail_default" style="color:rgb(51,51,153)">if you haven't had a chance to, </span>try running ICA with data prepped in different ways to find out for yourself how the ICA results change based on <span class="gmail_default" style="color:rgb(51,51,153)">different kinds of </span>data prepping</div><div style="color:rgb(51,51,153)"><div class="gmail_default" style="color:rgb(51,51,153)">********************************</div><br></div><div style="color:rgb(51,51,153)"><br></div></div></blockquote><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="color:rgb(51,51,153)"><br></div><div style="color:rgb(51,51,153)"><br></div><div style="color:rgb(51,51,153)"><br></div><div style="color:rgb(51,51,153)"><br></div><div style="color:rgb(51,51,153)"><br></div><div style="color:rgb(51,51,153)"><br></div><div style="color:rgb(51,51,153)"><br></div><div style="color:rgb(51,51,153)"><br></div><div style="color:rgb(51,51,153)"><br></div><div style="color:rgb(51,51,153)"><br></div><div style="color:rgb(51,51,153)"><br></div><div style="color:rgb(51,51,153)"><br></div><div style="color:rgb(51,51,153)"><br></div><div style="color:rgb(51,51,153)"><br></div><div style="color:rgb(51,51,153)"><br></div><div style="color:rgb(51,51,153)"><br></div><div style="color:rgb(51,51,153)"><br></div><div style="color:rgb(51,51,153)"><br></div><div style="color:rgb(51,51,153)"><br></div></div><br><div class="gmail_quote"><div dir="ltr">On Thu, Nov 29, 2018 at 2:42 AM Bert Vandenberghe <<a href="mailto:b.vandenberghe@kuleuven.be" target="_blank">b.vandenberghe@kuleuven.be</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">
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<p class="MsoNormal">Hello<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">For ICA decomposition, I read on your wikipage that you need at least (#channels^2*30) data points to perform ICA on epoched data.
<u></u><u></u></p>
<p class="MsoNormal">If not, ICA on continuous EEG is preferable.<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">In my case, I use 64 electrodes.<u></u><u></u></p>
<p class="MsoNormal">Does that mean that 4 minutes of epoched data would suffice in order to perform ICA ?
<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">I.e., 64^2*30 = 122880 data points<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">If you sample at 512 Hz:<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">512*240seconds=122880 data points<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">Is this a correct way of reasoning for deciding to perform ICA decomposition on epoched data ?<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">Thank you for your advice<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">Bert<u></u><u></u></p>
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