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<p class="MsoNormal">Dear list, <o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal" style="text-autospace:none">When calculating difference waves, I have found that when using pop_comperp the graph output differs from when I perform a subtraction in Matlab:<o:p></o:p></p>
<p class="MsoNormal" style="text-autospace:none">ERP1 = <span style="color:black">
mean(EEG.data,3); <o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="color:black">ERP2 = mean(EEG.data,3);</span><o:p></o:p></p>
<p class="MsoNormal">Difference_ERP = ERP1 – ERP2 ; <o:p></o:p></p>
<p class="MsoNormal">And plot this in a Matlab figure. <o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">The values are always larger in the Matlab figure, and look less like the difference ERP I’d expect, whereas the result of pop_comperp looks much more reasonable, as are the values. I’ve examined the pop_comperp function and it seems to
apply the same subtraction processes as the Matlab command line subtraction – so I cannot figure out why there’d be a disparity in results.
<o:p></o:p></p>
<p class="MsoNormal">I’d like to be able to extract data from these difference waves using Matlab for statistical analyses, but I’d like to understand why these results diverge in the first instance.
<o:p></o:p></p>
<p class="MsoNormal">Can anyone offer an explanation for why there’s a ‘difference’ in my difference waves?
<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Best, <o:p></o:p></p>
<p class="MsoNormal">Nicola<o:p></o:p></p>
<p class="MsoNormal"><o:p></o:p></p>
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