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<div class="moz-cite-prefix">Hi Akiko,<br>
<br>
of course you can use it, but freqanalysis will pad zeros thereby
increasing the spectral resolution but not add any data
specifically. In the end, your result will be a more smoothed
spectral estimate for the padded trials, which allows you to
average across trials with different length (since they the
spectral resolution is now equal across trials) or in this case
contrast conditions of different lengths. I don't see much sense
in doing that for the baseline, apart from tricking the algorithm,
but from a more pragmatic point of view: if no reviewer complaints
then it's fine ;) I bet there are some other consequences that I
don't foresee; if someone knows, please let me/us know :)<br>
<br>
Best,<br>
Jörn<br>
<br>
On 10/26/2012 4:52 PM, Akiko Ikkai wrote:<br>
</div>
<blockquote
cite="mid:CAKwx6QcJ7f7NAtFBrHzV10LudX0E1T0TZPjNo6WXz5N+cEwv7A@mail.gmail.com"
type="cite">Hi,
<div><br>
</div>
<div>I know this is not a recent post, but please allow me to ask
a follow-up question; can you use cfg.pad for ft_freqanalysis
for the baseline in this case (assuming post-baseline period of
interest is uniform length, say 1000ms)?</div>
<div><br>
</div>
<div>Such as:</div>
<div><font color="#33ff33">% extract baseline (500ms)</font></div>
<div>
<font color="#000099">cfg = [];<br>
cfg.toilim = [-.7 -.2];<br>
data_BL = ft_redefinetrial(cfg,ft_data);</font><br>
<br>
</div>
<div><font color="#33ff33">% pad to make it 1000ms and run
ft_freqanalysis</font></div>
<div><font color="#000099">cfg = [];<br>
<b>cfg.pad = 1;</b><br>
cfg.method = 'mtmfft';<br>
cfg.output = 'powandcsd';<br>
cfg.foi = foi;<br>
cfg.taper = 'dpss';<br>
cfg.tapsmofrq = smooth;<br>
freq_BL = ft_freqanalysis(cfg,data_BL);</font></div>
<div><font color="#000099"><br>
</font></div>
<div>Thanks! Akiko<br>
<br>
<div class="gmail_quote">On Mon, Jul 2, 2012 at 4:07 PM, Johanna
Zumer <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:johanna.zumer@donders.ru.nl" target="_blank">johanna.zumer@donders.ru.nl</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">Dear Anna,
<div><br>
</div>
<div>Ideally for the common filter, you want the same amount
of data T(s) per condition, where T = N x tw (and N is
number of trials and tw is timewindow length). In your
case, if the baselines for each conditions can be combined
into one general baseline, and if you happen to have 100
trials per condition, then T_baseline = 3 x 100 x 0.5s =
150s. If you then use 1.5s length post-baseline, then
T_each_condition = 100 x 1.5s = 150s, so you now have
equal T for each condition for the common filter.</div>
<div><br>
</div>
<div>However, in order to have an equal effect of tapers and
edge-effects on the different conditions, you should use
equal time window lengths in freqanalysis. Thus it would
be better to split your post-baseline data into 3 segments
of 500ms each before calling ft_freqanalysis, which again
gives T = 100 x 0.5 x 3 = 150s.</div>
<div><br>
</div>
<div>Cheers,</div>
<div>Johanna<br>
<br>
</div>
<div class="HOEnZb">
<div class="h5">
<div>
<div class="gmail_quote">2012/6/29 Anna Wilsch <span
dir="ltr"><<a moz-do-not-send="true"
href="mailto:wilsch@cbs.mpg.de" target="_blank">wilsch@cbs.mpg.de</a>></span><br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<br>
Dear Fieldtrippers,<br>
<br>
I'm trying to beamform my MEG data by building a
common filter including three conditions and a
baseline for each condition. The baseline
intervals have a duration of 500 ms. I was
wondering if it is ok if the post-baseline data
are longer than that (1000 - 2000 ms). Does it
have any negative impact on the
cross-spectral-density matrix and/or the common
filter? Would that still be a valid operation to
do or is it necessary that baseline and post
baseline data have the same length?<br>
Thank you for your comments.<br>
<br>
Cheers,<br>
Anna<br>
<br>
<br>
Anna Wilsch, Dipl.-Psych.<br>
Auditory Cognition Research Group<br>
Max Planck Institute for Human Cognitive and Brain
Sciences<br>
Stephanstr. 1a - Leipzig, Germany<br>
(p) <a moz-do-not-send="true"
href="tel:%2B49%20%280%29341%209940%202641"
value="+4934199402641" target="_blank">+49
(0)341 9940 2641</a><br>
(e) <a moz-do-not-send="true"
href="mailto:wilsch@cbs.mpg.de" target="_blank">wilsch@cbs.mpg.de</a><br>
<br>
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</blockquote>
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<br>
<br clear="all">
<div><br>
</div>
-- <br>
<font><span style="font-family:arial,helvetica,sans-serif">Akiko
Ikkai, Ph.D. <br>
Postdoctoral Fellow<br
style="font-family:arial,helvetica,sans-serif">
</span></font><font
style="font-family:arial,helvetica,sans-serif"
face="'PrimaSans BT,Verdana,sans-serif'">Department of
Psychological and Brain Sciences<br>
Johns Hopkins University<br>
Ames Hall, 3400 N. Charles St.<br>
Baltimore, MD 21218</font><br
style="font-family:arial,helvetica,sans-serif">
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</blockquote>
<br>
<br>
<pre class="moz-signature" cols="72">--
Jörn M. Horschig
PhD Student
Donders Institute for Brain, Cognition and Behaviour
Centre for Cognitive Neuroimaging
Radboud University Nijmegen
Neuronal Oscillations Group
FieldTrip Development Team
P.O. Box 9101
NL-6500 HB Nijmegen
The Netherlands
Contact:
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Tel: +31-(0)24-36-68493
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Visiting address:
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NL-6525 EN Nijmegen
The Netherlands</pre>
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