<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Dear Keith,<div><br></div><div>Not sure which technique is the best, but you should try testing existing techniques on a good subject first to see if you get anything at all.</div><div><br></div><div>I think the most used technique to isolate the induce response consists in [1] computing the power spectrum of the ERP averaged across trials, [2] computing the average power spectrum of the single-trial ERP, [3] subtract 1 from 2.</div><div><br></div><div>Another technique consists in directly subtracting the mean ERP from each single-trial, and computing the power spectrum on the centred data, see ref:</div><div><br></div><div><div>Rousselet, G. A., Husk, J. S., Bennett, P. J., & Sekuler, A. B. (2007). Single-trial EEG dynamics of object and face visual processing. Neuroimage, 36(3), 843-862.</div> </div><div><br></div><div>The function to compute time-frequency decompositions is newtimef. </div><div><br></div><div>The different steps of the 2 techniques above can easily be implemented using this function. For instance, you can compute centred data at one electrode E to feed into newtimef by doing:</div><div>data = squeeze(EEG.data(E,:,:)) - repmat(mean(squeeze(EEG.data(E,:,:)),2),1,size(EEG.data,3));</div><div><br></div><div>Best,</div><div><br></div><div>GAR</div><div><br></div><div><br></div><div><br></div><div><br><div><div>On 23 Sep 2009, at 16:11, Keith Yoder wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div>Hi all,<br></div><div></div><div>I know that this problem has been discussed to some extent already (e.g. <a href="http://sccn.ucsd.edu/pipermail/eeglablist/2008/002262.html">http://sccn.ucsd.edu/pipermail/eeglablist/2008/002262.html</a>), but I've been unable to find a define solution. What I'm attempting to do is the portion of the response that is induced, rather than evoked.</div> <div></div><div>Our paradigm involves a computer screen with five sections, each flickering at a different frequency. At any given time, one of the sections is cued (the section is surrounded by a a bright red line). We are attempting to identify induced changes time-locked to cue shifts. I know that other authors have had some success using the following general procedure:</div> <div> 1. Compute the time-domain average (ERP)</div><div> 2. Perform a Fourier transform on the time-domain average</div><div> 3. Subtract the Fourier transform coefficients from the Fourier transform coefficients of each single trial</div> <div> 4. Calculate the amplitude spectrum of the subtracted Fourier coefficents at each trial</div><div>In theory, the resulting amplitude spectrum from step 4 should isolate the induced response. Before I implement the above steps, I wanted to ask this list for opinions.</div> <div></div><div>Have others on this list found the procedure to be the most effective method for isolating induced responses? If not, what methods have proved to be more effective? Finally, are there EEGLAB functions that can be manipulated (either by the appropriate parameters or by small changes to the code itself) to perform some or all of the above steps?</div> <div></div><div>Thanks in advance,</div><div>Keith</div><div>--</div><div>Research Aide</div><div>Belmonte Autism Lab</div><div>Cornell University</div> _______________________________________________<br>Eeglablist page: <a href="http://sccn.ucsd.edu/eeglab/eeglabmail.html">http://sccn.ucsd.edu/eeglab/eeglabmail.html</a><br>To unsubscribe, send an empty email to <a href="mailto:eeglablist-unsubscribe@sccn.ucsd.edu">eeglablist-unsubscribe@sccn.ucsd.edu</a><br>For digest mode, send an email with the subject "set digest mime" to <a href="mailto:eeglablist-request@sccn.ucsd.edu">eeglablist-request@sccn.ucsd.edu</a></blockquote></div><br><div apple-content-edited="true"> <span class="Apple-style-span" style="font-size: 12px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 18px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font: normal normal normal 12px/normal Helvetica; min-height: 14px; "><br class="Apple-interchange-newline"><br></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font: normal normal normal 12px/normal Helvetica; min-height: 14px; "><br></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">************************************************************************************</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><b style="font-weight: bold; "><span class="Apple-style-span" style="font-weight: bold; "><span class="Apple-style-span" style="font-weight: bold; "><span class="Apple-style-span" style="font-weight: bold; "><span class="Apple-style-span" style="font-weight: bold; "><span class="Apple-style-span" style="font-weight: bold; "><span class="Apple-style-span" style="font-weight: bold; "><span class="Apple-style-span" style="font-weight: bold; "><span class="Apple-style-span" style="font-weight: bold; "><span class="Apple-style-span" style="font-weight: bold; "><span class="Apple-style-span" style="font-weight: bold; "><span class="Apple-style-span" style="font-weight: bold; "><span class="Apple-style-span" style="font-weight: bold; "><span class="Apple-style-span" style="font-weight: bold; "><span class="Apple-style-span" style="font-weight: bold; ">Guillaume A. 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The problem is that governments, even neoconservative governments, rarely get the chance to prove their sacred theory right: despite their enormous ideological advances, even George Bush's Republicans are, in their own minds, perennially sabotaged by meddling Democrats, intractable unions, and alarmist environmentalists." </div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><i style="font-style: italic; "><br class="khtml-block-placeholder"></i></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><span class="Apple-tab-span" style="white-space: pre; "><span class="Apple-style-span" style="white-space: pre; "> </span></span>Naomi Klein - No War - America's real business in Iraq - 2005</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">************************************************************************************</div><div><br class="khtml-block-placeholder"></div><div><br class="khtml-block-placeholder"></div><br class="Apple-interchange-newline"></span><br class="Apple-interchange-newline"></div></span></div></span> </div><br></div></body></html>