difference between mtmconvol and mtmfft

[Stan van Pelt]

Dear Thomas,

If I understand you correctly you applied ft_freqanalysis_mtmfft on a piece
of data that looked interesting based on ft_freqanalysis_mtmconvol, but this
gives slightly different results.

Please let someone correct me if I'm wrong, but what I think is going on is
that for the calculation of power in a time-freq bin,
ft_freqanalysis_mtmconvol uses data from adjacent time windows (because of
the temporal smoothing). ft_freqanalysis_mtmconvol on the other hand only
uses the data that is within your time-freq bin, because the temporal
analysis window is equal to the size (along the temporal dimension) of the
input data.

Best,
Stan

Stan van Pelt, PhD
Donders Institute for Brain, Cognition and Behaviour, Radboud University
Nijmegen
Kapittelweg 29, 6525 EN Nijmegen, Netherlands
E-mail:  stan.vanpelt at donders.ru.nl
Website: www.ru.nl/donders/
Phone: 	 (+31) (0)24 36 68495
Fax: 	 (+31) (0)24 36 10989


-----Original Message-----
From: FieldTrip discussion list [mailto:FIELDTRIP at NIC.SURFNET.NL] On Behalf
Of Thomas Hartmann
Sent: Tuesday, August 17, 2010 4:52 PM
To: FIELDTRIP at NIC.SURFNET.NL
Subject: [FIELDTRIP] difference between mtmconvol and mtmfft

  hi,
from the descriptions of the two functions ft_freqanalysis_mtmconvol and
ft_freqanalysis_mtmfft i thought that those two functions should work
more or less equivalent - the first just doing it multiple times to get
a time-frequency representation.
to localize a significant cluster from my tf-representation, i
recalculated the fft (including the csd, of course) using the exact same
arguments for latency, window-size, frequency, padding, taper etc....
but the results do differ. not dramatically but considerably. does
anyone have an explanation for this?

thanks a lot in advance,
thomas

--
Dipl. Psych. Thomas Hartmann

OBOB-Lab
University of Konstanz
Department of Psychology
P.O. Box D25
78457 Konstanz
Germany

Tel.: +49 (0)7531 88 4612
Fax: +49 (0)7531-88 4601
Email: thomas.hartmann at uni-konstanz.de
Homepage: http://www.uni-konstanz.de/obob

"I am a brain, Watson. The rest of me is a mere appendix. " (Arthur Conan
Doyle)

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The aim of this list is to facilitate the discussion between users of the
FieldTrip  toolbox, to share experiences and to discuss new ideas for MEG
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The aim of this list is to facilitate the discussion between users of the FieldTrip  toolbox, to share experiences and to discuss new ideas for MEG and EEG analysis. See also http://listserv.surfnet.nl/archives/fieldtrip.html and http://www.ru.nl/neuroimaging/fieldtrip.