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<p style="color: rgb(0, 0, 0); font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt;">
Dear Makoto,<br>
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Thank you so much for the link!! I still have two questions:<br>
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(1) Since dB is the log ratio of two same quantities, so in the spectopo plot <span style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 16px; background-color: rgb(255, 255, 255);">10log</span><sub style="font-family: Calibri, Arial, Helvetica, sans-serif; background-color: rgb(255, 255, 255);">10</sub><span style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 16px; background-color: rgb(255, 255, 255);">(</span><span style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 16px; color: rgb(33, 33, 33); background-color: rgb(255, 255, 255);">uV^2/Hz) </span>, does
EEGlab implicitly assume that the reference level is 1uV<span style="color: rgb(33, 33, 33); font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 16px; background-color: rgb(255, 255, 255);">^2</span> ?<br>
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<br>
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<p><span style="font-size: 12pt;">(2) The script line "</span><span style="color: rgb(255, 0, 0); font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12.6666669845581px;">deltaPower = mean(10.^(spectra(deltaIdx)/10)); </span><span style="font-size: 12pt;">"
gives </span><span style="color: rgb(33, 33, 33); font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 16px; background-color: rgb(255, 255, 255);">uV^2/Hz, which is the mean value of densities</span><span style="font-size: 12pt;">. If I hope to
get the total power within alpha band, what script should I write? </span>Intuitively it seems something like: total power=sum(10.^(spectra(<span style="font-size: 12pt;">alphaIdx)/10)</span><span style="font-size: 12pt;">*(</span><span style="font-size: 12pt;">length
of each discrete frequency</span><span style="font-size: 12pt;">)</span><span style="font-size: 12pt;">).</span><span style="font-size: 12pt;"> </span><span style="font-size: 12pt;"> </span><span style="font-size: 12pt;">I</span><span style="font-size: 12pt;">s
this concept</span><span style="font-size: 12pt;"> correc</span><span style="font-size: 12pt;">t? If it is correct, then what should be the value for "</span><span style="font-size: 12pt;">length of each discrete frequency" (say for 128Hz sampling rate)? If
not, then is there actually any method to get the total power?</span></p>
<p><span style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 16px; background-color: rgb(255, 255, 255);"><br>
</span></p>
<p>Best wishes,<br>
</p>
<p style="color: rgb(0, 0, 0); font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt;">
SHAN Xin<br>
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<br>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>From:</b> Makoto Miyakoshi <mmiyakoshi@ucsd.edu><br>
<b>Sent:</b> Wednesday, 22 April 2015 2:07 AM<br>
<b>To:</b> #SHAN XIN#<br>
<b>Cc:</b> eeglablist@sccn.ucsd.edu<br>
<b>Subject:</b> Re: [Eeglablist] How can I get the power of each frequency band?</font>
<div> </div>
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<div>
<div dir="ltr">Dear Shan,
<div><br>
</div>
<div>> Why divided by Hz?<br>
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<div><br>
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<div>Here is (esoteric) discussion about the related topic. </div>
<div><a href="http://sccn.ucsd.edu/pipermail/eeglablist/2014/008224.html">http://sccn.ucsd.edu/pipermail/eeglablist/2014/008224.html</a><br>
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<div><br>
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<div>Makoto</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Mon, Apr 20, 2015 at 3:58 AM, #SHAN XIN# <span dir="ltr">
<<a href="mailto:SHAN0055@e.ntu.edu.sg" target="_blank">SHAN0055@e.ntu.edu.sg</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex; border-left-width:1px; border-left-color:rgb(204,204,204); border-left-style:solid; padding-left:1ex">
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<div>Hi Makoto,</div>
<div><br>
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<div>Oh I didn't realize the scale on the figure might already in dB...is it? I know dB is defined as log ratio, but uV^2/Hz does not seem to be a ratio since the units (volt square and hz) do not match... Also, do you therefore mean that the definition of
absolute power is <span>uV^2/Hz?</span></div>
<div><br>
</div>
<div>I've gone through the related topics in archives and still don't understand these... I also search on Google but still cannot find a clear explanation. Why divided by Hz?</div>
<span class="">
<div><br>
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<div>Thank you so much!!</div>
<div><br>
</div>
<div>Shan Xin</div>
</span>
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<div class="h5">
<div><br>
#SHAN XIN# <<a href="mailto:SHAN0055@e.ntu.edu.sg" target="_blank">SHAN0055@e.ntu.edu.sg</a>> 於 Apr 20, 2015 17:29 寫道：<br>
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<p>Dear Makoto,<br>
</p>
<p><br>
</p>
<p>I have a doubt for the power unit. I read the "help spectopo" in Matlab, for the variable "spectra":<br>
</p>
<p><br>
</p>
<div>Outputs:</div>
<div> spectra = (nchans,nfreqs) power spectra (mean power over epochs), in dB</div>
<div> freqs = frequencies of spectra (Hz)<br>
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<div><br>
</div>
<div>If the unit of variable "spectra" is in dB unit already, then when computing the absolute power, do we still need to do the transformation as you suggested (i.e.
<span style="color:rgb(255,0,0); font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12.6666669845581px; background-color:rgb(255,255,255)">
10.^(spectra(deltaIdx)/10)</span>)? <br>
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<div><br>
</div>
<div>I know when plotting the figure, the spectrum is plotted in log scale. But if the unit of spectra is in dB, then there's no need to transform, right? <br>
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<div><br>
</div>
<div>I don't know if this is correct... Could you look more into it? Thank you so much!!<br>
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<div><br>
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<div>Shan Xin<br>
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<div dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>From:</b> Makoto Miyakoshi <<a href="mailto:mmiyakoshi@ucsd.edu" target="_blank">mmiyakoshi@ucsd.edu</a>><br>
<b>Sent:</b> Thursday, 16 April 2015 11:11 AM<br>
<b>To:</b> #SHAN XIN#<br>
<b>Cc:</b> <a href="mailto:eeglablist@sccn.ucsd.edu" target="_blank">eeglablist@sccn.ucsd.edu</a><br>
<b>Subject:</b> Re: [Eeglablist] How can I get the power of each frequency band?</font>
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<div><span style="color:rgb(0,0,0); font-family:Calibri,Arial,Helvetica,sans-serif; font-size:16px">Dear Shan,</span></div>
<span style="color:rgb(0,0,0); font-family:Calibri,Arial,Helvetica,sans-serif; font-size:16px">
<div><span style="color:rgb(0,0,0); font-family:Calibri,Arial,Helvetica,sans-serif; font-size:16px"><br>
</span></div>
> I'm not very proficient in Matlab programming...</span><br>
<div class="gmail_extra"><br>
</div>
<div class="gmail_extra">This could be a concern but you can try!</div>
<div class="gmail_extra"><br>
</div>
<div class="gmail_extra">
<div style="font-size:12.6666669845581px">%%%%%%%%%%%%%%%%%%%</div>
<div style="font-size:12.6666669845581px">
<div>
<div>% for your epoched data, channel 2</div>
<div>[spectra,freqs] = spectopo(EEG.data(2,:,:), 0, EEG.srate);</div>
<div><br>
</div>
<div>% delta=1-4, theta=4-8, alpha=8-13, beta=13-30, gamma=30-80</div>
<div>deltaIdx = find(freqs>1 & freqs<4);</div>
<div>thetaIdx = find(freqs>4 & freqs<8);</div>
<div>alphaIdx = find(freqs>8 & freqs<13);</div>
<div>betaIdx = find(freqs>13 & freqs<30);</div>
<div>gammaIdx = find(freqs>30 & freqs<80);</div>
<div><br>
</div>
<div><font color="#ff0000">% compute absolute power</font></div>
<div><font color="#ff0000">deltaPower = mean(10.^(spectra(deltaIdx)/10));</font></div>
<div><font color="#ff0000">thetaPower = mean(10.^(spectra(thetaIdx)/10));</font></div>
<div><font color="#ff0000">alphaPower = mean(10.^(spectra(alphaIdx)/10));</font></div>
<div><font color="#ff0000">betaPower = mean(10.^(spectra(betaIdx)/10));</font></div>
<div><font color="#ff0000">gammaPower = mean(10.^(spectra(gammaIdx)/10));</font></div>
</div>
<div>%%%%%%%%%%%%%%%%%</div>
<div><br>
</div>
<div>Makoto</div>
</div>
</div>
<div class="gmail_extra"><br>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Tue, Apr 14, 2015 at 6:23 AM, #SHAN XIN# <span dir="ltr">
<<a href="mailto:SHAN0055@e.ntu.edu.sg" target="_blank">SHAN0055@e.ntu.edu.sg</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex; border-left-width:1px; border-left-color:rgb(204,204,204); border-left-style:solid; padding-left:1ex">
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<p><span style="font-size:12pt">Hi EEGLab team,</span></p>
<div dir="ltr" style="color:rgb(33,33,33)">
<div>
<div style="font-size:12pt; color:rgb(0,0,0); font-family:Calibri,Arial,Helvetica,sans-serif; background-color:rgb(255,255,255)">
<div><br>
Does EEGlab has plugin or script so that I can get the power of individual band (e.g. power of alpha band or beta band) from your computation, instead of just a continuous line in the power spectrum figure? I'm not very proficient in Matlab programming...t<span style="font-size:12pt">hank
you so much!!</span></div>
<div><br>
</div>
<div>Best wishes,<br>
</div>
<div>SHAN Xin<br>
</div>
<div><br>
</div>
<div><br>
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<br>
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-- <br>
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<div dir="ltr">Makoto Miyakoshi<br>
Swartz Center for Computational Neuroscience<br>
Institute for Neural Computation, University of California San Diego<br>
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-- <br>
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<div dir="ltr">Makoto Miyakoshi<br>
Swartz Center for Computational Neuroscience<br>
Institute for Neural Computation, University of California San Diego<br>
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