<div dir="ltr">Hi Neil,<div><br></div><div>It seems to me like it would in fact be better to submit all the data to the same ICA decomposition, especially if you plan on comparing them, since you would want any differences you do observe to be based on the tasks themselves, rather than differences you introduced by running different compositions (and perhaps removing different components). Indeed, in most ERP research comparing different conditions, one would still expect underlying neural activity to show [slight] differences between conditions, but trials of the different conditions are still usually combined in the same ICA decomposition. See the following message for more discussion of this (as well as discussion of how you could go about the analysis using separate ICAs): <a href="http://sccn.ucsd.edu/pipermail/eeglablist/2011/003694.html">http://sccn.ucsd.edu/pipermail/eeglablist/2011/003694.html</a> </div><div><div><br></div><div>Also, as an aside, you asked if it matters whether the epochs are different lengths; I'm not sure EEGLAB can handle epochs of differing lengths anyway? To do that, you may need to use an additional plugin, or try Fieldtrip, or concatenate the epochs to look like continuous data (which may raise other issues; this has been discussed on the list before, but I don't recall the details).</div><div><br></div><div>Best,</div><div>Steve</div><div><br></div></div></div><div class="gmail_extra"><br clear="all"><div><div class="gmail_signature"><div dir="ltr"><div><br><br></div>Stephen Politzer-Ahles<br>New York University, Abu Dhabi<br>Neuroscience of Language Lab<br><a href="http://www.nyu.edu/projects/politzer-ahles/" target="_blank">http://www.nyu.edu/projects/politzer-ahles/</a><br></div></div></div>
<br><div class="gmail_quote">On Fri, May 29, 2015 at 7:43 AM, Neil Bailey <span dir="ltr"><<a href="mailto:neil.bailey@monash.edu" target="_blank">neil.bailey@monash.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">Hi all<div><br></div><div>Does anyone have a good sense on whether it would be valid to combine epochs from the same EEG session, but different tasks in order to maximise data for ICA decomposition?</div><div><br></div><div>I'm aware that feeding more data into the ICA gets better results, and the data from the different tasks will have similar artifacts to be removed (eye movement, muscle, line noise). However, the underlying neural activity will differ between the tasks (for example the Sternberg working memory task generates a large amount of posterior alpha, while the Go/Nogo task does not, but does generate a large N2 and P3 component).</div><div><br></div><div>Will the differences in the underlying neural activity between tasks negatively affect the results of the ICA if activity from different tasks is combined? And will it matter if the epochs from different tasks are of different lengths?</div><div><br></div><div>Kind regards,<span class="HOEnZb"><font color="#888888"><br clear="all"><div><br></div>-- <br><div><div dir="ltr"><div><div dir="ltr"><div>Neil Bailey (PhD)</div><div>Monash Alfred Psychiatry Research Centre</div><div><a href="mailto:Neil.Bailey@Monash.edu" target="_blank">Neil.Bailey@Monash.edu</a></div><div>(03) 9076 5032</div></div></div></div></div>
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