<html><head><style type="text/css"><!-- DIV {margin:0px;} --></style></head><body><div style="font-family:arial,helvetica,sans-serif;font-size:10pt"><div><br></div><div style="font-family: arial,helvetica,sans-serif; font-size: 10pt;"><br>
hello,<br>
<br>thank you for the answers, especially for Mr. Andrew Hill and Mr. Tarik S Bel-Bahar<br>I apologize for my ambiguous and unclear question. It caused by my English is bad, i'm sorry.<br><br>I
will explain about my experiment, now i'm doing my final project to get
bachelor degree's. I try to generate ERP with subject read an
alphabet/letter in a slideshow ( I chosed a/i/u/e/o letter for stimuli).
My goal is to get a ERP waveform related to a certain alphabet which
subject has read. Note that subject only thinking reading a words not
speak it and not produce any sound. The subject just say (or think) the
letter in mind.<br><br>for my question number :<br><br>1.thank you for
the suggestion, I take just 20 trials for each letter, actually I wanted
to do experiment (record many trials) again but i'm
facing a bit of problem here. To do an experiment, I must rent an EEG
in medical clinic which I must paid some money (unfortunately it quite
expensive). because of that I can't do an experiment as many as I
wanted.<br><br>2. I mean many N trials in many N epoch (is that right ?) and single-trial in 1 epoch.<br><br><div style="text-align: left;">3.
Let me try to explain what I understand. To extract ERP there are two
ways : a. Do the averaging many trials and b. run ICA to the data. And
what I'm going to do is run ICA first, then I will average the result of
ICA decomposition<br></div><br><br>I admit I do not fully understand
ICA, but I still try reading the literature (it's little hard in
English, hehehe). There is a question in my mind, how do we prove the
result of ICA decomposition is right ? I mean, do the result will one
hundred percent represent the true neural signal ? <br><br>thank you very much<br><br>regards,<br>bagas isadewa<br><div style="font-family: times new roman,new york,times,serif; font-size: 12pt;"><font face="Tahoma" size="2"><hr size="1"><b><span style="font-weight: bold;">From:</span></b> Tarik S Bel-Bahar <tarikbelbahar@gmail.com><br><b><span style="font-weight: bold;">To:</span></b> Bagas Isadewa <izadewa@yahoo.com><br><b><span style="font-weight: bold;">Cc:</span></b> EEGLAB <eeglablist@sccn.ucsd.edu><br><b><span style="font-weight: bold;">Sent:</span></b> Mon, December 27, 2010 8:45:01 AM<br><b><span style="font-weight: bold;">Subject:</span></b> Re: [Eeglablist] (ask) about averaging and ICA<br></font><br><div>Greetings Bagas,</div>
<div> </div>
<div>1. Yes, there are multiple papers that refer to this issue. I would suggest you start</div>
<div>with the HANDBOOKS by Tom Handy or Steve Luck, and these will answer your basic questions about the relations</div>
<div>between trial counts, averaged ERPs, and the resultant signal-to-noise ratios. </div>
<div>You can find these books by doing a Google search, and you can order them from Amazon or another bookseller.</div>
<div>Here's the link for the Handy handbook: <a rel="nofollow" target="_blank" href="http://mitpress.mit.edu/catalog/item/default.asp?tid=10253&ttype=2">http://mitpress.mit.edu/catalog/item/default.asp?tid=10253&ttype=2</a></div>
<div> </div>
<div>2. Your second question is not clear. It's not clear what you mean by "many trials" or only "single-trials" in one epoch.</div>
<div>For information about best practice using EEGLAB and ICA, please read through the EEGLAB tutorial online.</div>
<div>A general rule of thumb is that more single trials are better than fewer single trials, for an accurate ICA decomposition of the data.</div>
<div> </div>
<div>3. Again, you should read and learn basic information about ERP techniques from handbooks mentioned in Point 1 above,</div>
<div>or in articles that use ERPs (please search on Google Scholar for examples that relate to your research questions). </div>
<div>It also not clear what you mean by using "only one technique".</div>
<div>You can generate average ERPs without using ICA, and you can also generate ERPs after using ICA.</div>
<div>Please be aware that the emphasis in EEGLAB is on single-trial analysis, although it can certainly be used for single subject average ERPs.</div>
<div> </div>
<div>4. In the future please try to be more specific about what you are trying to do, what kind of ERPs you are trying to generate.</div>
<div>Also it seems that you are unaware of the the many potential uses of ICA (for artifact detection, for detection of independent modulators, etc..)</div>
<div>Please read through the articles describing EEGLAB (which you can find at the EEGLAB site, or via Google Scholar).</div>
<div>Please also read through and do the EEGLAB tutorial, which will answer some of your questions.</div>
<div>Then feel free to send some more questions after that.</div>
<div> </div>
<div>Good luck Bagas!</div>
<div> </div>
<div> </div>
<div> </div>
<div><br> </div>
<div class="gmail_quote">On Thu, Dec 23, 2010 at 1:09 AM, Bagas Isadewa <span dir="ltr"><<a rel="nofollow" ymailto="mailto:izadewa@yahoo.com" target="_blank" href="mailto:izadewa@yahoo.com">izadewa@yahoo.com</a>></span> wrote:<br>
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<div>hello,<br><br>i have several questions, <br><br>1. if I wanted to average EEG data to yields good ERP, how many minimum trials do I needed ? is there any paper or journals that explained about it ?<br>2. then, if I wanted to run ICA to extract ERP, do I need many trials or only single-trials in one epoch will be enough ??<br>
3. is it necessary to run ICA first then do averaging or it is enough to use only one technique for extracting ERP ?<br><br>if you don't mind please give me an explanation<br>thank you very much<br><br><br>regards,<br>
bagas isadewa<br><br></div></div><br></div><br>_______________________________________________<br>Eeglablist page: <a rel="nofollow" target="_blank" href="http://sccn.ucsd.edu/eeglab/eeglabmail.html">http://sccn.ucsd.edu/eeglab/eeglabmail.html</a><br>
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