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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Hi EEGLABERs, <o:p></o:p></p>
<p class="MsoNormal">I have been looking into ‘newcrossf’ function and the way it calculates coherence for epoched data. Basically, it uses the ‘timefreq’ function to calculate the time/frequency decomposition the data. ‘timefreq’ function treats the epoched
data as a continuous one:<o:p></o:p></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:"Courier New";color:black"><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:"Courier New";color:black">X = reshape(X, g.frame, g.trials);</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:"Courier New";color:black">[alltfX freqs timesout] = timefreq(X, g.srate, spectraloptions{:});</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:"Courier New";color:black"><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:"Courier New";color:black">Y = reshape(Y, g.frame, g.trials);<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:"Courier New";color:black">[alltfY] = timefreq(Y, g.srate, spectraloptions{:});</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">and calculates the its spectrum using the whole data which is now concatenated version of all trials. So, for each of channel’s pair (X and Y , for example) the spectrum is calculated as described above and then the joint time-freq decomposition
is calculated for coherence value.<o:p></o:p></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:"Courier New";color:black"><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:"Courier New";color:black">coherres = sum(alltfX .* conj(alltfY), 3) ./ sqrt( sum(abs(alltfX).^2,3) .* sum(abs(alltfY).^2,3) );</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><b>However, similar to the ERSP concept, each trial/epoch might be different than others [because of perturbations in subjects’ mental status, mental fatigue, etc] and thus I think it is more appropriate to calculate the coherence for each
trial first and then make the average across trials.<o:p></o:p></b></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Any thoughts?<o:p></o:p></p>
<p class="MsoNormal">Iman <o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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