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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Hi FieldTrippers,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Following up on this conversation. It
seems that the ‘induced activity’ contains both phase-locked and
non-phase-locked activity, whereby the ‘evoked’ activity contains
only phase-locked activity. Is it then kosher to separate these components by
linear subtraction? For example, if we first compute the ‘induced’
activity by averaging power over individual trials, and from that subtract the
‘evoked activity’ (calculated based on average response) to get the
induced activity without any phase-locked activity?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>So if <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Induced = Phase + Non-Phase<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>And <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Evoked = Phase<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Then <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Non-Phase = Induced – Evoked<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Or does the fact that this is a linear
operations on data that have been constructed through a non-linear process
render this somehow invalid? It has certainly been done before. Your comments
would be much appreciated.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Cheers,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Thomas<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<div style='border:none;border-left:solid blue 1.5pt;padding:0pt 0pt 0pt 4.0pt'>
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<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'> FieldTrip
discussion list [mailto:<st1:PersonName w:st="on">FIELDTRIP@NIC.SURFNET.NL</st1:PersonName>]
<b><span style='font-weight:bold'>On Behalf Of </span></b>Christian Hesse<br>
<b><span style='font-weight:bold'>Sent:</span></b> Thursday, February 22, 2007
3:41 AM<br>
<b><span style='font-weight:bold'>To:</span></b> <st1:PersonName w:st="on">FIELDTRIP@NIC.SURFNET.NL</st1:PersonName><br>
<b><span style='font-weight:bold'>Subject:</span></b> Re: [FIELDTRIP]
Estimating the power in EEG frequency bands</span></font><o:p></o:p></p>
</div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Hi Shantanu,<o:p></o:p></span></font></p>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
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<div>
<div>
<blockquote style='margin-top:5.0pt;margin-bottom:5.0pt' type=cite>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>When I want to analyze the power in different eeg frequency bands
(alpha,<span class=apple-converted-space> </span><o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>beta, etc), do I use a grand average for all subjects, or do i take
only<span class=apple-converted-space> </span><o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>data trial by trial for all electrodes, estimate the powers, and then<span
class=apple-converted-space> </span><o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>average them for all trials?<o:p></o:p></span></font></p>
</div>
</blockquote>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
</div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>You use the the latter approach, averaging the power over trials
(subject average) and then over subjects (grand average) if you wish to look at
INDUCED activity, i.e. task or event related modulation in the amplitude
time-course of ongoing oscillatory activity (this analysis is not sensitive to
the phase differences of the oscillations on different trials).<o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>You can also average the signals first (in the time domain) and then
compute the power spectrum, in which case you will see the spectral properties
of EVOKED activity, i.e., activity that is phase or time locked to the event /
stimulus / response.<o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Both of these time frequency visualizations give information that is
complementary to looking a the time course of your event-related or evoked
potentials (for EEG) or fields (for MEG) which you get by doing a time-locked
average of the raw signals.<o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Hope this helps to clarify,<o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Christian<o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
</div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<div><span style='border-spacing: 0px 0px;text-align:auto;-khtml-text-decorations-in-effect: none;
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style='border-spacing: 0px 0px;text-align:auto;-khtml-text-decorations-in-effect: none;
-apple-text-size-adjust: auto;orphans: 2;widows: 2;word-spacing:0px'>----------------------------------------------------------------------<o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=1 color=black face=Helvetica><span
style='font-size:6.5pt;font-family:Helvetica;color:black'>Christian Hesse, PhD,
MIEEE<o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=1 color=black face=Helvetica><span
style='font-size:6.5pt;font-family:Helvetica;color:black'><o:p> </o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=1 color=black face=Helvetica><span
style='font-size:6.5pt;font-family:Helvetica;color:black'>F.C. Donders Centre
for Cognitive Neuroimaging <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><st1:address w:st="on"><st1:Street w:st="on"><font size=1
color=black face=Helvetica><span style='font-size:6.5pt;font-family:Helvetica;
color:black'>P.O. Box</span></font></st1:Street><font size=1 color=black
face=Helvetica><span style='font-size:6.5pt;font-family:Helvetica;color:black'>
9101</span></font></st1:address><font size=1 color=black face=Helvetica><span
style='font-size:6.5pt;font-family:Helvetica;color:black'> <o:p></o:p></span></font></p>
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<p class=MsoNormal><font size=1 color=black face=Helvetica><span
style='font-size:6.5pt;font-family:Helvetica;color:black'>NL-6500 HB Nijmegen <o:p></o:p></span></font></p>
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<p class=MsoNormal><font size=1 color=black face=Helvetica><span
style='font-size:6.5pt;font-family:Helvetica;color:black'>The <st1:country-region
w:st="on"><st1:place w:st="on">Netherlands</st1:place></st1:country-region><o:p></o:p></span></font></p>
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style='font-size:6.5pt;font-family:Helvetica;color:black'><o:p> </o:p></span></font></p>
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<div>
<p class=MsoNormal><font size=1 color=black face=Helvetica><span
style='font-size:6.5pt;font-family:Helvetica;color:black'>Tel.: +31 (0)24 36
68293<o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=1 color=black face=Helvetica><span
style='font-size:6.5pt;font-family:Helvetica;color:black'>Fax: +31 (0)24 36
10989<o:p></o:p></span></font></p>
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<p class=MsoNormal><font size=1 color=black face=Helvetica><span
style='font-size:6.5pt;font-family:Helvetica;color:black'><o:p> </o:p></span></font></p>
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<div>
<p class=MsoNormal><font size=1 color=black face=Helvetica><span
style='font-size:6.5pt;font-family:Helvetica;color:black'>Email: <a
href="mailto:c.hesse@fcdonders.ru.nl">c.hesse@fcdonders.ru.nl</a><o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=1 color=black face=Helvetica><span
style='font-size:6.5pt;font-family:Helvetica;color:black'>Web: <a
href="http://www.fcdonders.ru.nl">www.fcdonders.ru.nl</a><o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=1 color=black face=Helvetica><span
style='font-size:6.5pt;font-family:Helvetica;color:black'>----------------------------------------------------------------------<o:p></o:p></span></font></p>
</div>
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<p class=MsoNormal><font size=1 color=black face=Helvetica><span
style='font-size:6.5pt;font-family:Helvetica;color:black'><o:p> </o:p></span></font></p>
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