<html><head><style type='text/css'>p { margin: 0; }</style></head><body><div style='font-family: Times New Roman; font-size: 12pt; color: #000000'><font size="3" style="font-family: 'Times New Roman';">Dear Beom Jun,</font><br><br><font size="3" style="font-family: 'Times New Roman';">I see multiple scenarios why this baseline activity decrease could happen. First of all, how the component you're rejecting look like (i.e. "blink component")? Do you see this activity decrease after the baseline period?</font><div style="font-family: 'Times New Roman'; font-size: 12pt;"><br></div><div style="font-family: 'Times New Roman'; font-size: 12pt;">The "quality" of the ICA decomposition, how well your artifact/component of interest has been isolated by algorithm in time (i.e. blink time courses) and space (marked frontal topography), will determine the activity that later on you'll reject/select. If your decomposition is not well suited, the rejection of a particular IC activity might have "extra" activity you don't want to reject (effect of interest), might be the algorithm is not able to isolate the components of interests (i.e. artifacts) or a combination of both.</div><div style="font-family: 'Times New Roman'; font-size: 12pt;"><br></div><div style="font-family: 'Times New Roman'; font-size: 12pt;">To evaluate the quality of your ICA decomposition you might have a look here (<a href="http://www.ncbi.nlm.nih.gov/pubmed/19162199" style="font-size: 12pt;">http://www.ncbi.nlm.nih.gov/pubmed/19162199</a><span style="font-size: 12pt;">). Basically, the authors find that the ICA decomposition improves significantly "</span><span style="font-family: arial, helvetica, clean, sans-serif; font-size: 13.333333969116211px; line-height: 18.88888931274414px; background-color: rgb(255, 255, 255);">increased by removing the mean EEG at each channel for each epoch of data rather than the mean EEG in a prestimulus baseline"</span><span style="font-size: 12pt;">. In addition (see here: </span><a href="http://sccn.ucsd.edu/pipermail/eeglablist/2012/004925.html" style="font-size: 12pt;">http://sccn.ucsd.edu/pipermail/eeglablist/2012/004925.html</a><span style="font-size: 12pt;">), high-pass filtering above ~1hz improve the results.</span></div><div style="font-family: 'Times New Roman'; font-size: 12pt;"><span style="color: rgb(46, 46, 46); font-family: 'Arial Unicode MS', 'Arial Unicode', Arial, 'URW Gothic L', Helvetica, Tahoma, sans-serif; font-size: 13px; line-height: 20px; text-align: justify; word-spacing: -1px; background-color: rgb(255, 255, 255);"><br></span></div><div><font face="times new roman, new york, times, serif">It's very important to feed ICA as much relevant data as you can use. The more the data, the better the decomposition. There's a rule of thumb that says that for a reliable IC decomposition<span style="color: rgb(46, 46, 46); line-height: 20px; text-align: justify; word-spacing: -1px; background-color: rgb(255, 255, 255);"> 20 time points per channel</span><sup style="border: 0px; margin: 0px; padding: 0px; line-height: 0; color: rgb(46, 46, 46); text-align: justify; word-spacing: -1px; background-color: rgb(255, 255, 255);">2 </sup></font><span style="font-family: 'times new roman', 'new york', times, serif;">is needed (see here for a reference </span><a href="http://www.ncbi.nlm.nih.gov/pubmed/16904745">http://www.ncbi.nlm.nih.gov/pubmed/16904745</a><span style="font-family: 'times new roman', 'new york', times, serif;">)</span><span style="font-family: 'times new roman', 'new york', times, serif;"> </span></div><div style="font-family: 'Times New Roman'; font-size: 12pt;"><br></div><div style="font-family: 'Times New Roman'; font-size: 12pt;">I hope that helps,</div><div style="font-family: 'Times New Roman'; font-size: 12pt;"><br></div><div style="font-family: 'Times New Roman'; font-size: 12pt;">Diego<br><hr id="zwchr"><blockquote style="border-left:2px solid rgb(16, 16, 255);margin-left:5px;padding-left:5px;"><b>From: </b>"Beom Jun Min" <mbj0310@gmail.com><br><b>To: </b>"FieldTrip discussion list" <fieldtrip@science.ru.nl><br><b>Sent: </b>Monday, 24 June, 2013 6:27:47 AM<br><b>Subject: </b>[FieldTrip] Decreased baseline level after using ICA in ERP data<br><br><div dir="ltr">Dear all,<div><br></div><div style="">I have ERP data and now I am dealing with ICA to remove muscle and eye artifacts. </div><div>However, I found that after ft_rejectcomponent, the baseline level of the segmented epoch decreased. (The baselinewindow is [-0.2 0].)</div>
<div>The baseline level decreased even though I rejected only one component. </div><div><br></div><div style="">My script is shown below.</div><div><br></div><div><div><i>%% Removing the Artifacts</i></div><div><i>cfg = [];<br>
</i></div><div><i>cfg.component = [ ]; % to be removed component(s)</i></div><div><i>post_ICA_temp6 = ft_rejectcomponent(cfg, comp_detrand, data_raw);</i></div><div><i><br></i></div><div><i>%% timelocking</i></div><div><i><br>
</i></div><div><i>cfg = [];</i></div><div><i>timelock_temp6 = ft_timelockanalysis(cfg, post_ICA_temp6);</i></div><div><i><br></i></div><div><i>%% Plot</i></div><div><i><br></i></div><div><i>figure;</i></div><div><i>cfg = [];</i></div>
<div><i>cfg.layout = lay;</i></div><div><i>cfg.interactive = 'yes';</i></div><div><i>cfg.channel = ['all', {'-EKG', '-EMG'}];</i></div><div><i>ft_multiplotER(cfg, timelock_temp6)</i><br></div>
</div><div><br></div><div>Is there something that I missed?<br></div><div><br></div><div style="">Thanks.</div><div style=""><br></div><div style="">BJ</div><div><div><br></div>-- <br><div dir="ltr"><div><font face="arial, helvetica, sans-serif">BeomJun Min, M.D.</font></div>
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<br>_______________________________________________<br>fieldtrip mailing list<br>fieldtrip@donders.ru.nl<br>http://mailman.science.ru.nl/mailman/listinfo/fieldtrip</blockquote><br><br><br>-- <br><div><span name="x"></span>PhD Student<br>Neuronal Oscillations Group<br>Donders Institute for Brain, Cognition and Behaviour <br>Centre for Cognitive Neuroimaging<br>Radboud University Nijmegen <br>NL-6525 EN Nijmegen<br>The Netherlands<br>http://www.ru.nl/people/donders/lozano-soldevilla-d/<span name="x"></span><br></div></div></div></body></html>