<div dir="ltr">Dear Jet,<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">> I</span><span style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">CA has been performed for the two datasets separately.</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">Good. </span></div><div>The basic rule is that removing an electrode cap and new ICA is necessary, unless you can replicate the original cap/electrode location with sub-millimeter precision.<br></div><div><a href="https://sccn.ucsd.edu/wiki/Makoto's_preprocessing_pipeline#General_tips_for_performing_ICA_.2806.2F26.2F2018_updated.29">https://sccn.ucsd.edu/wiki/Makoto's_preprocessing_pipeline#General_tips_for_performing_ICA_.2806.2F26.2F2018_updated.29</a><br></div><div><br></div><div><div style="font-size:small;text-decoration-style:initial;text-decoration-color:initial"><span style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">> I understand that that is why I get to see the warning I mentioned</span><span style="font-size:small;text-decoration-style:initial;text-decoration-color:initial;background-color:rgb(255,255,255);float:none;display:inline">.</span><br></div><br class="gmail-Apple-interchange-newline">There is EEGLAB 'session' which, I believe, is supposed to use 'same subject but different capping'. However, I often simply regard the same subject different sessions as different subjects. This way you can avoid troubles you experienced.</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">> Should this be possible?<span> </span></span><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"><span><br></span></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"><span>No. You can't 'merge' different sessions (i.e., different capping) from the same subject. EEGLAB's 'merge' only works if and only if ICA-related matrices are shared and identical (i.e.,  paired t-test is possible).</span></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"><span><br></span></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"><span><span style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">> However, since the two datasets have been aqcuired on two separate days I understand that ICA analyses should be performed on the datasets separately. </span><br></span></span></div><div><br></div><div>You should treat them as if the data were from different subjects (i.e., you have to use two-sample t-test)</div><div><br></div><div>Makoto</div><br><div class="gmail_quote"><div dir="ltr">On Tue, Jul 17, 2018 at 10:34 PM Jet Zoon <<a href="mailto:jetzoon@gmail.com">jetzoon@gmail.com</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">Dear eeglablist,</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">In using eeglab to perform analyses for a study with a rather complex design I ran into the following warning: Warning: ***** change STUDY design as it combines datasets with different ICA decompositions.<br></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">A short description of the design: </div><div style="font-size:small;text-decoration-style:initial;text-decoration-color:initial">testday 1: participants receive a high-energy savoury meal</div><div style="font-size:small;text-decoration-style:initial;text-decoration-color:initial">testday 2: participants receive a<span> </span><span style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">high-energy</span><span> </span>sweet meal<br></div><div style="font-size:small;text-decoration-style:initial;text-decoration-color:initial">Before and after meal intake we measured neural responses (using EEG) to visual and olfactory stimuli of the following categories:</div><div style="font-size:small;text-decoration-style:initial;text-decoration-color:initial">High-energy savoury food</div><div style="font-size:small;text-decoration-style:initial;text-decoration-color:initial"><span style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">High-energy sweet food</span><br></div><div style="font-size:small;text-decoration-style:initial;text-decoration-color:initial"><span style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">Low-energy savoury</span> food<br></div><div style="font-size:small;text-decoration-style:initial;text-decoration-color:initial"><span style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">Low-energy sweet food</span><br></div><div style="font-size:small;text-decoration-style:initial;text-decoration-color:initial"><span style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">Non-food</span></div><div style="font-size:small;text-decoration-style:initial;text-decoration-color:initial"><span style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">Baseline (no product/no odour)</span></div><div style="font-size:small;text-decoration-style:initial;text-decoration-color:initial"><span style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">Each stimulus category was presented 18 times before and 18 times after meal intake.</span></div><div style="font-size:small;text-decoration-style:initial;text-decoration-color:initial"><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 style="font-size:small;text-decoration-style:initial;text-decoration-color:initial"><span style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">To keep the statistical power as high as possible, with the limited amount of items we presented, I would like to combine stimulus categories between the two test sessions. I think that it is best to end up with the stimulus categories: fully congruent (between meal and stimulus: e.g. High-energy sweet meal - high-energy sweet odour), taste congruent, energy congruent, not congruent, non-food and baseline. </span></div><div style="font-size:small;text-decoration-style:initial;text-decoration-color:initial"><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 style="font-size:small;text-decoration-style:initial;text-decoration-color:initial">I now included data from two sessions on two separate days i<span style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">n the study dataset</span>. ICA has been performed for the two datasets separately. I understand that that is why I get to see the warning I mentioned<span style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">.</span> However, in contrast to what is mentioned in an earlier conversation on this topic (<a href="https://sccn.ucsd.edu/pipermail/eeglablist/2011/003669.html" style="color:rgb(17,85,204)" target="_blank">https://sccn.ucsd.edu/pipermail/eeglablist/2011/003669.html</a>), I can run the analyses and get my results. </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">Should this be possible? Can I just interpret the results as usual or does combining items from two datasets provide invalid results? If so, is there another option to combine the items from the two datasets? In the message I referred to, it is suggested to only merge sessions with the same ICA decomposition. However, since the two datasets have been aqcuired on two separate days I understand that ICA analyses should be performed on the datasets separately. </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 really appreciate your help in resolving this problem. </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">Kind regards,</div><div style="font-size:small;text-decoration-style:initial;text-decoration-color:initial">Jet Zoon</div>

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