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<p>Hi Bob <br>
</p>
<p>I certainly think your suggestion to "delete the one second of
data" is preferable, if thats all there were to it. But there are
two additional things to consider - <br>
</p>
<p>(1) Many EEG studies are in populations, or use experimental
paradigms, where inevitably there will be an
eye-blink/eye-movement on a large fraction of trials. <br>
</p>
<p>(2) I believe manual editing as you describe is also highly
subjective, as is the selection of ICA components to remove. We
usually only remove the eye-movement component. <br>
</p>
<p>In my opinion, there really is no such thing as artifact-free
data, except for narrow-band signals like SSVEPs. <br>
</p>
<p> ramesh<br>
</p>
<p> <br>
</p>
<div class="moz-cite-prefix">On 06/14/2017 03:15 PM, Robert Thatcher
wrote:<br>
</div>
<blockquote
cite="mid:837110672.9892572.1497478557088@mail.yahoo.com"
type="cite">
<meta http-equiv="Context-Type" content="text/html; charset=UTF-8">
<div>
<div>
<div>Ramesh,</div>
</div>
<div> Thank you for your post and I agree that artifact is
broad-band and superimposed on many if not all of the EEG
channels. Reconstruction therefore will necessarily change
relative phase which can be seen in the waves themselves and
is accumulative in the average phase differences between
channels. As for your concern "<span>It's not obvious to me
to prefer the original relative phase with the artifact
components." I believe that you should have no concern
because the original phase differences that are artifact
free are real and produced by the underlying physiology and
represent the summation of LFP due to synaptic rise times
and synaptic integration times and conduction velocities
between groups of neurons in networks of the brain. The
original phase differences must be preserved and not altered
in any manner if one wants to study brain networks and
dynamics.</span></div>
<div><span><br>
</span></div>
<div><span>The simple solution is to not use ICA for artifact
rejection and instead use algorhythms to delete the parts of
the record that have artifact and retain the parts of the
original record with no </span><span
class="ydp5308b4ffApple-converted-space">artifact. Because
of the stochastic and nonstationarity of the EEG as one
increases the sample size then one converges toward the
stable and reproducabe average of the instantaneous phase
differences between channels that is not corrupted by
artifact. ICA reconstruction alters an entire 5 minute EEG
recording even if there is ony a single 1 second of eye
movement artifact. Why not simply delete the one second
artifact and then work with the remaining 4 minutes and 59
seconds?</span></div>
<div><span class="ydp5308b4ffApple-converted-space"><br>
</span></div>
<div><span class="ydp5308b4ffApple-converted-space">ICA is
excellent for feature detection and can serve as "seeds" to
guide further cross-spectral analyses only if the phase
differences in the original recording are preserved.</span></div>
<div><span class="ydp5308b4ffApple-converted-space"><br>
</span></div>
<div><span class="ydp5308b4ffApple-converted-space">Bob</span></div>
<div><span class="ydp5308b4ffApple-converted-space"><br>
</span></div>
<div><span class="ydp5308b4ffApple-converted-space"><br>
</span></div>
<div><br>
</div>
<div><br>
</div>
<div id="ydp293668c9yahoo_quoted_7519025489"
class="ydp293668c9yahoo_quoted">
<div>
<div>On Wednesday, June 14, 2017, 4:46:34 PM EDT, Ramesh
Srinivasan <a class="moz-txt-link-rfc2396E" href="mailto:r.srinivasan@uci.edu"><r.srinivasan@uci.edu></a> wrote:</div>
<div><br>
</div>
<div><br>
</div>
<div>
<div id="ydp293668c9yiv0275212460">
<div>
<p>Hi All - <br>
</p>
<p>I think Bob is right that the relative phase will
be changed by deleting 1 or 2 artifact components.
Any artifact is broad-band and hence has components
in each frequency bin. When reconstructing the (in
this example, 19) channels, the relative phases will
change because some of the signal in each frequency
bin has been removed when using only 17 or 18
components. <br>
</p>
<p>The open question is whether the original relative
phase or the ICA-corrected relative phase is the
better estimate of the relative phase between the
populations that contributed to each electrode.
It's not obvious to me to prefer the original
relative phase with the artifact components. <br>
</p>
<p>Part of the problem for me (and I do use EEGLAB's
ica) about identifying components as artifact in the
ICA is that I don't think they contain just the
artifact, they also contain some genuine brain
activity that we are removing. This bothers me, but
I don't know a better solution. Even the case of
the eye-movement artifact components is likely a
mixture. <br>
</p>
<p>I'd like to see this discussion move away from
algorithm to this harder question about artifact
removal. <br>
</p>
<p>ramesh <br>
</p>
<p><br>
</p>
<div class="ydp293668c9yiv0275212460yqt3095400500"
id="ydp293668c9yiv0275212460yqt85155">
<div class="ydp293668c9yiv0275212460moz-cite-prefix">On
06/14/2017 10:43 AM, Robert Thatcher wrote:<br>
</div>
<blockquote type="cite"> </blockquote>
</div>
</div>
<div class="ydp293668c9yiv0275212460yqt3095400500"
id="ydp293668c9yiv0275212460yqt25440">
<div>
<div>
<div>
<p
class="ydp293668c9yiv0275212460ydp76ba64cbMsoNormal"><span>Iman,</span></p>
<p
class="ydp293668c9yiv0275212460ydp76ba64cbMsoNormal"><span>
Thank you for the information. I could only
find a power point attachment of a
simulation in your post. I did not find a
scientific publication where you compared
the phase differences changes between an
original EEG recording and a ICA
reconstruction after removing one or more
components. Please re-send your study.
Also please give the citation to any of your
publications or other’s publications where
phase differences were compared between the
original EEG recording and post ICA
reconstruction. It will be interesting to
see if you found similar changes like in the
study by Montefusco-Siegmund et al or by
Georges Otte or even in the example pre vs
post data files that you can download from
the internet. I am assuming that you have
downloaded the EEG data and then used a JTFA
like the Hilbert transform or even the FFT
cross-spectrum to prove to yourself that the
phase differences between the original and
the ICA reconstruction have not been
preserved.</span></p>
<p
class="ydp293668c9yiv0275212460ydp76ba64cbMsoNormal"><span> </span></p>
<p
class="ydp293668c9yiv0275212460ydp76ba64cbMsoNormal"><span>As
for the mathematics concerning
reconstruction from a lower dimensional
matrix to a higher dimensional matrix where
there are no simple linear transforms I
refer you to Taken’s theorem where “<span>The
reconstruction preserves the properties of
the dynamical system that do not change
under smooth coordinate changes, but it
does not preserve the geometric shape of
structures in phase space.</span>” Also,
in standard differential geometry math
courses the issue of lower dimensional
manifold mapping to higher dimensional
manifolds shows a loss of information in all
cases. Also, commonsense operates here
where one tries to reconstruct 19 channels
of EEG using only 15 or 16 or 17 ICA
components hence a loss of information.</span></p>
<p
class="ydp293668c9yiv0275212460ydp76ba64cbMsoNormal"><span> </span></p>
<p
class="ydp293668c9yiv0275212460ydp76ba64cbMsoNormal"><span>Finally,
the brain is not a total chaotic organ. As
demonstrated by many scientists (e.g.,
Nunez; Walter Freeman; Roberto-Pascual
Marqui; E. Roy John; Joel Lubar; etc)
coherence and phase differences are well
behaved and highly reproducible within and
between subjects. Coherence and phase are
dependent on the number and strength of
connections between groups of neurons. Here
is a URL to a study that tested Paul Nunez’s
two-compartmental model of Coherence and
Phase Differences and found that these
measures vary as a function of distance and
packing density:</span></p>
<p
class="ydp293668c9yiv0275212460ydp76ba64cbMsoNormal"><span><a
moz-do-not-send="true" shape="rect"
href="http://www.appliedneuroscience.com/TWO-COMPARTMENTAL_MODEL_EEG_COHERENCE.pdf"
rel="nofollow" target="_blank">http://www.appliedneuroscience.com/TWO-COMPARTMENTAL_MODEL_EEG_COHERENCE.pdf</a></span></p>
<p
class="ydp293668c9yiv0275212460ydp76ba64cbMsoNormal"><span> </span></p>
<p
class="ydp293668c9yiv0275212460ydp76ba64cbMsoNormal"><span>Here
is a url to a study that used EEG LORETA
correlations to replicate Diffusion Tensor
Imaging measures of connectivity in the
brain:</span></p>
<p
class="ydp293668c9yiv0275212460ydp76ba64cbMsoNormal"><span><a
moz-do-not-send="true" shape="rect"
href="http://www.appliedneuroscience.com/DTI-ThatcherHumanBrainmapping.pdf"
rel="nofollow" target="_blank">http://www.appliedneuroscience.com/DTI-ThatcherHumanBrainmapping.pdf</a></span></p>
<p
class="ydp293668c9yiv0275212460ydp76ba64cbMsoNormal"><span> </span></p>
<p
class="ydp293668c9yiv0275212460ydp76ba64cbMsoNormal"><span>Here
is a url to a study that measured phase lock
and phase shift duration from birth to about
16 years of age in 458 and where phase
differences were stable and well behaved: <a
moz-do-not-send="true" shape="rect"
class="ydp293668c9yiv0275212460moz-txt-link-freetext"
href="http://www.appliedneuroscience.com/PhaseresetDevelopment.pdf"
rel="nofollow" target="_blank">http://www.appliedneuroscience.com/PhaseresetDevelopment.pdf</a></span></p>
<p
class="ydp293668c9yiv0275212460ydp76ba64cbMsoNormal"><span> </span></p>
<p
class="ydp293668c9yiv0275212460ydp76ba64cbMsoNormal"><span>If
you do a search of the National Library of
Medicine database (Pubmed) using the search
terms “EEG coherence” you will find 2,874
citations. There is huge consistency in
this vast literature which would be
impossible if the brain was totally chaotic.</span></p>
<p
class="ydp293668c9yiv0275212460ydp76ba64cbMsoNormal"><span> </span></p>
<p
class="ydp293668c9yiv0275212460ydp76ba64cbMsoNormal"><span>Best
regards,</span></p>
<p
class="ydp293668c9yiv0275212460ydp76ba64cbMsoNormal"><span> </span></p>
<p
class="ydp293668c9yiv0275212460ydp76ba64cbMsoNormal"><span>Robert</span></p>
</div>
</div>
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