Dear Anette,<br><br>If you are looking at the steady state response and are interested in its power only, you should not try to achieve the highest frequency resolution, but rather adjust the parameters (sampling rate and NFFT) to place your SSR frequency exactly in the center of the frequency bin, which may be rather large (around 1 hz). <br>
<br>In this way you'd be sure you're capturing all the power coming from from the SSR and will be able to compare this frequency bin between conditions or to the nearby frequency bins.<br><br>Katya<br><br><br><div class="gmail_quote">
2009/12/17 Anette Giani <span dir="ltr"><<a href="mailto:anette.giani@tuebingen.mpg.de">anette.giani@tuebingen.mpg.de</a>></span><br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
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<p class="MsoNormal"><span style="font-size: 12pt; line-height: 115%; font-family: "Cambria","serif";">Dear all,</span></p>
<p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal;"><span style="font-size: 12pt; font-family: "Cambria","serif";">I
am a beginner on MEG and I have some basic questions on Fourier transformation
using the function </span><span style="font-size: 12pt; font-family: "Cambria","serif"; color: black;">freqanalysis_mtmfft</span><span style="font-size: 12pt; font-family: "Cambria","serif";">. It would be great if you could help me!</span></p>
<p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal;"><span style="font-size: 12pt; font-family: "Cambria","serif";"> </span></p>
<p class="MsoNormal"><span style="font-size: 12pt; line-height: 115%; font-family: "Cambria","serif";">We are interested in Steady State Responses. Therefore we
recorded data 60 seconds trials. </span></p>
<p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal;"><span style="font-size: 12pt; font-family: "Cambria","serif";">To
transform the time domain into a frequency spectrum we used the function </span><span style="font-size: 12pt; font-family: "Cambria","serif"; color: black;">freqanalysis_mtmfft.
However, I am not sure which </span><span style="font-size: 12pt; font-family: "Cambria","serif";">value </span><span style="font-size: 10pt; font-family: "Courier New";">cfg.tapsmofrq</span><span style="font-size: 12pt; font-family: "Cambria","serif";">. Since we would like to
have the highest frequency resolution possible I set cfg.tapsmofrq to 0.25; the
lowest value possible. Do you think that was a good choice? Further, does this
value mean that our lowest possible frequency resolution would be 0.25? If that
was the case, how could I avoid all smoothing?</span></p>
<p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal;"><span style="font-size: 12pt; font-family: "Cambria","serif";"> </span></p>
<p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal;"><span style="font-size: 12pt; font-family: "Cambria","serif";">Second,
do you think that it would be useful to pad the signal with zeros to
artificially increase the frequency resolution? I guess this could be done
using cfg.pad?</span></p>
<p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal;"><span style="font-size: 12pt; font-family: "Cambria","serif";"> </span></p>
<p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal;"><span style="font-size: 12pt; font-family: "Cambria","serif";">Lastly,
an even more general question: What do you think would be handier: (1) Compute
the frequency spectrum over 60 seconds, to get a high frequency resolution or
(2) to cut the signal into e.g. 4 second pieces and to average all spectra to
increase the signal to noise ratio?</span></p>
<p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal;"><span style="font-size: 12pt; font-family: "Courier New";"> </span></p>
<p class="MsoNormal"><span style="font-size: 12pt; line-height: 115%; font-family: "Cambria","serif";">Thanks a lot in advance for your help,</span></p>
<p class="MsoNormal"><span style="font-size: 12pt; line-height: 115%; font-family: "Cambria","serif";"> Anette</span></p>
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</blockquote></div><br><br clear="all"><br>-- <br>Ekaterina Vinnik, MD, PhD<br>Tactile Perception and Learning Lab<br>Cognitive neuroscience sector, <br>SISSA,<br>Trieste,<br>Italy<br><br>+393347032225<br><a href="mailto:lulswinnik@gmail.com">lulswinnik@gmail.com</a><br>
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<p>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.</p>
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<p> http://www.ru.nl/fcdonders/fieldtrip/</p>