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<div><font size="3">Dear All</font></div>
<div><font size="3"> </font></div>
<div><font size="3">I am trying to compute power in the mu frequency range, 8-13 Hz.</font></div>
<div><font size="3">I've tried 3 different methods for doing this which I thought would be broadly equivalent: However, for the same data, I get very different results depending on the method I use.</font></div>
<div><font size="3">If results were just a linear transform of one another, I would not be bothered, but it’s more serious than that.</font></div>
<div><font size="3">I am comparing power for 5 different conditions, and when I plot the power for each condition, the pattern of results across conditions is completely different depending on what I do.</font></div>
<div><font size="3">I've provided my pared-down scripts below. I'd be grateful if someone could let me know if I’m doing something wrong, or if I've just misunderstood how these functions work. </font></div>
<div><font size="3">I’d be happy to provide fuller examples if need be.</font></div>
<div><font size="3"> I'm running eeglab6.1 with matlabR2009b. Many thanks</font></div>
<div><font size="3"> </font></div>
<div><font size="3">With the identical data, I have tried:</font></div>
<div>%1. Using FFT via newtimef,</div>
<div>%mydata is subset of EEG.data for trials for given condition and electrode, squeezed to 2D</div>
<div>mydata=squeeze(EEG.data(18,:,:));%electrode 18 is C3</div>
<div>cycles=0;</div>
<div>[ersp,itc,powbase,times,freqs]=...</div>
<div> newtimef( mydata,EEG.pnts,[EEG.xmin EEG.xmax]*EEG.srate, EEG.srate, cycles, 'baseline',NaN,'plotitc','off','plotersp','off');</div>
<div>murange = find(freqs>8 & freqs<13);</div>
<div>mypowermean=(mean(ersp(murange,:),2));</div>
<div>allmu=mean(mypowermean)</div>
<div><br>
</div>
<div> </div>
<div>%2. Using spectopo,</div>
<div>% thisdata is subset of trials from EEG data for 1 electrodes and a given condition</div>
<div>thisdata=EEG.data(18,:,:);</div>
<div>[spectra,freqs] = spectopo(thisdata, 0, EEG.srate,'plot','off');</div>
<div>murange2 = find(freqs>8 & freqs<13);</div>
<div>allmu2 = mean(spectra(murange2),2)</div>
<div> </div>
<div>%3. Computing power from EEG.data after bandpass filtering at 8-13 Hz</div>
<div>% mydata is EEG.data for given electrode and condition, squeezed to 2D</div>
<div>f1=8;f2=13;</div>
<div>EEG= pop_eegfilt(EEG,0,f2, [], [0]); % Low pass filter with cutoff freq f2 Hz</div>
<div>EEG = eeg_checkset(EEG );</div>
<div>EEG= pop_eegfilt(EEG,f1,0, [], [0]); % High pass filter with cutoff freq f1 Hz</div>
<div>EEG = eeg_checkset(EEG );</div>
<div>mydata=squeeze(EEG.data(18,:,:));%electrode 18 is C3</div>
<div>mydamean=mean(mydata,2);</div>
<div>mydavoltsq=mydamean.^2;</div>
<div>myvoltsq=mean(mydavoltsq);</div>
<div>allmu3=10*log10(myvoltsq/10);</div>
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<div class="PlainText">Dorothy Bishop, Professor of Developmental Neuropsychology,<br>
Dept of Experimental Psychology, University of Oxford, OX1 3UD.<br>
tel +44 (0)1865 271369; fax +44 (0)1865 281255;<br>
WEB: <a href="http://www.psy.ox.ac.uk/oscci" target="_blank" style="font-family:Calibri,sans-serif; font-size:15px"><font color="#0070C0">www.psy.ox.ac.uk/oscci</font></a><br>
Blog: <a href="http://deevybee.blogspot.com/">http://deevybee.blogspot.com/</a></div>
<div class="PlainText">Raising Awareness of Language Learning Impairments! See <a href="http://www.youtube.com/RALLIcampaign">
www.youtube.com/RALLIcampaign</a></div>
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