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The next revision of EEGLAB (within one or two weeks) will allow to
force the use of double precision numbers. Just for info, although no
message is sent to the eeglabnews list, a new revision of EEGLAB is
issued every few weeks. The changes compared to the previous official
version are relatively important especially concerning STUDYes (about
200 improvements or bug fixes). We will eventually compile an
explanatory document with all these changes to issue a new EEGLAB
official release but even to date the detail for all the changes is
reported on the download page.<br>
<br>
Arno<br>
<!----><br>
<blockquote
cite="mid:001401c8a137$8cc14a10$a643de30$@gomezherrero@tut.fi"
type="cite">
<pre wrap="">In my opinion this is definitely not the best practice because MATLAB
support for single precision data is still quite unstable and important
MATLAB features will not work properly with single precision data. For
instance, MATLAB's Signal Processing Toolbox does not accept single
precision data. See the MATLAB's SPT product overview here, under Supported
data types:
<a class="moz-txt-link-freetext" href="http://www.mathworks.com/access/helpdesk/help/toolbox/signal/">http://www.mathworks.com/access/helpdesk/help/toolbox/signal/</a>
In my opinion MATLAB's developers are making little effort to stress the
fact that "If you input single-precision floating-point or integer data, you
should not expect to receive correct results". To be precise they should say
that you should expect wrong results... Before I became aware of this, I was
happily using single precision data but after a painful error debugging
experience I gave it up almost completely (unless memory constraints force
me using single precision). The big problem here is that, if you use single
precision with MATLAB's SPT you might get completely well formatted ouputs
which will not trigger any error in your code but that are completely wrong!
Therefore finding such an error can be really difficult. And I am not sure
whether this problems with single precision data occur in other MATLAB
toolboxes or even in some of the built-in MATLAB functions.
</pre>
<blockquote type="cite">
<pre wrap="">I've just upgraded from EEGLab 4.515 to 6.x and I've noticed that the
data
are not stored in the EEG.data structure as single precision numbers.
In my
experimentation, I found that runica in some cases does yield different
results for double vs. single precision data.
Is there a quick and easy way to change the representation of the data
in
EEGLab 6.x back to double precision representation?
</pre>
</blockquote>
<pre wrap=""><!---->
As far as I know this was not possible in the current version of EEGLAB. I
have modified slightly functions eeg_checkset.m, eeg_options.m and
eeg_optionsbackup.m in order to allow the user choose whether to use single
precision or not. You can get the modified versions here:
<a class="moz-txt-link-freetext" href="http://www.cs.tut.fi/~gomezher/nosingle.zip">http://www.cs.tut.fi/~gomezher/nosingle.zip</a>
You just need to change the default EEGLAB functions in the folder
functions/adminfunc/ with the ones I modified. After that EEGLAB will store
the data by default in double precision. However, the user can return easily
to the default single precision using the EEGLAB menu File>Memory. I would
suggest EEGLAB´s developers to include this option in future releases of
EEGLAB.
Hope that helps,
Germán
</pre>
<blockquote type="cite">
<pre wrap="">
Regards,
Phil Zeman
----- Original Message -----
From: "Julie Onton" <a class="moz-txt-link-rfc2396E" href="mailto:julie@sccn.ucsd.edu"><julie@sccn.ucsd.edu></a>
To: <a class="moz-txt-link-rfc2396E" href="mailto:sklein@berkeley.edu"><sklein@berkeley.edu></a>
Cc: <a class="moz-txt-link-rfc2396E" href="mailto:eeglablist@sccn.ucsd.edu"><eeglablist@sccn.ucsd.edu></a>
Sent: Monday, April 14, 2008 4:16 PM
Subject: Re: [Eeglablist] Time-frequency analysis (subtraction first or
analysis first)
</pre>
<blockquote type="cite">
<pre wrap="">I agree that the time/frequency analysis should be performed first,
</pre>
</blockquote>
<pre wrap="">and
</pre>
<blockquote type="cite">
<pre wrap="">THEN subtraction.
Subtraction of the EEG time courses (ie, in the time domain) will
</pre>
</blockquote>
<pre wrap="">give a
</pre>
<blockquote type="cite">
<pre wrap="">very different result
compared to the (frequency domain) ERSP subtraction. EEGLAB's
</pre>
</blockquote>
<pre wrap="">newtimef()
</pre>
<blockquote type="cite">
<pre wrap="">called from the
commandline performs this very operation on two datasets
</pre>
</blockquote>
<pre wrap="">corresponding to
</pre>
<blockquote type="cite">
<pre wrap="">two different
conditions.
Best, Julie
--
Julie Onton, PhD
Swartz Center for Computational Neuroscience
Institute for Neural Computation
University of California, San Diego
(858) 458-1927 ext 17
<a class="moz-txt-link-freetext" href="http://sccn.ucsd.edu/~julie">http://sccn.ucsd.edu/~julie</a>
</pre>
<blockquote type="cite">
<pre wrap="">Dear Arnaud,
Are you sure about your recommendation of the first statement being
correct?
Suppose the two conditions happen to be quite similar in producing
</pre>
</blockquote>
</blockquote>
<pre wrap="">alpha
</pre>
<blockquote type="cite">
<blockquote type="cite">
<pre wrap="">or
gamma oscillations. Since the two conditions are the same, one would
</pre>
</blockquote>
</blockquote>
<pre wrap="">like
</pre>
<blockquote type="cite">
<blockquote type="cite">
<pre wrap="">the desired outcome to be a *cancellation *of the two power plots.
However,
since the occurrence of the oscillations likely happen at different
</pre>
</blockquote>
</blockquote>
<pre wrap="">time
</pre>
<blockquote type="cite">
<blockquote type="cite">
<pre wrap="">points (and with different phases) early subtraction would still
</pre>
</blockquote>
</blockquote>
<pre wrap="">leave
</pre>
<blockquote type="cite">
<blockquote type="cite">
<pre wrap="">the
oscillations and the outcome would be equal or even stronger power
</pre>
</blockquote>
</blockquote>
<pre wrap="">rather
</pre>
<blockquote type="cite">
<blockquote type="cite">
<pre wrap="">than cancellation. Or am I thinking about it improperly?
Stan
On Sun, Apr 13, 2008 at 10:53 AM, Arnaud Delorme <<a class="moz-txt-link-abbreviated" href="mailto:arno@cerco.ups">arno@cerco.ups</a>-
</pre>
</blockquote>
</blockquote>
<pre wrap="">tlse.fr>
</pre>
<blockquote type="cite">
<blockquote type="cite">
<pre wrap="">wrote:
</pre>
<blockquote type="cite">
<pre wrap="">Dear Hsu,
only your first statement is correct. The second one could be
</pre>
</blockquote>
</blockquote>
</blockquote>
<pre wrap="">correct if
</pre>
<blockquote type="cite">
<blockquote type="cite">
<blockquote type="cite">
<pre wrap="">you could pair the trials, but it would be very rare that you would
</pre>
</blockquote>
</blockquote>
</blockquote>
<pre wrap="">want
</pre>
<blockquote type="cite">
<blockquote type="cite">
<blockquote type="cite">
<pre wrap="">to do this (since trials are recorded at different times and are
</pre>
</blockquote>
</blockquote>
</blockquote>
<pre wrap="">usually
</pre>
<blockquote type="cite">
<blockquote type="cite">
<blockquote type="cite">
<pre wrap="">not paired between conditions). Look up the help of the newtimef
function which allows computing differences between power between
different conditions and newcrossf which allows computing
</pre>
</blockquote>
</blockquote>
</blockquote>
<pre wrap="">difference
</pre>
<blockquote type="cite">
<blockquote type="cite">
<blockquote type="cite">
<pre wrap="">between phase coherence images.
Best,
Arno
Hsu, Shen-Mou wrote:
</pre>
<blockquote type="cite">
<pre wrap="">Dear list-memebers,
Suppose that I am interested in comparing two conditions A and B
</pre>
</blockquote>
</blockquote>
</blockquote>
</blockquote>
<pre wrap="">in
</pre>
<blockquote type="cite">
<blockquote type="cite">
<blockquote type="cite">
<pre wrap="">terms of their power and phase coherence. I was wondering which one
</pre>
</blockquote>
</blockquote>
</blockquote>
<pre wrap="">of
</pre>
<blockquote type="cite">
<blockquote type="cite">
<blockquote type="cite">
<pre wrap="">the
following steps is more theoretically correct. 1. After
</pre>
</blockquote>
</blockquote>
</blockquote>
<pre wrap="">segmentation,
</pre>
<blockquote type="cite">
<blockquote type="cite">
<blockquote type="cite">
<pre wrap="">calculate the EEG differences between the condition A and B and
</pre>
</blockquote>
</blockquote>
</blockquote>
<pre wrap="">then
</pre>
<blockquote type="cite">
<blockquote type="cite">
<blockquote type="cite">
<pre wrap="">perform
time-frequency analysis on the differences. 2. After segmentation,
perform
time-frequency analysis on the EEG data of the condition A and B
respectively and then compute the power or phase coherence
</pre>
</blockquote>
</blockquote>
</blockquote>
<pre wrap="">differences
</pre>
<blockquote type="cite">
<blockquote type="cite">
<blockquote type="cite">
<pre wrap="">between two conditions. Any comments would be much appreciated.
</pre>
<blockquote type="cite">
<pre wrap="">Many thanks,
Shen-Mou Hsu
</pre>
</blockquote>
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</blockquote>
</blockquote>
</blockquote>
<pre wrap="">to
</pre>
<blockquote type="cite">
<blockquote type="cite">
<blockquote type="cite">
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