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<p>Hello everyone,<br>
<br>
My name is Erik Nickel, I am currently working at the University
of Tartu. I need advice regarding time-frequency analysis of EEG
data in the context of language development research with
children diagnosed with developmental language disorder (DLD),
specifically focusing on Estonian-speaking children.<br>
<br>
We have been conducting an auditory oddball paradigm study,
where we collected EEG data using a 32-channel BioSemi system.
Prior to analysis, we preprocessed the data using the MADE
pipeline, which is based on EEGLAB. The preprocessing steps
included highpass filtering at 0.3Hz, lowpass filtering at 50Hz,
and baseline correction using a baseline period of [-100 0] ms.
The epochs were defined from -1500 ms to 2300 ms around the
stimulus onset, with our primary time of interest being [0 700]
ms post-stimulus onset.<br>
<br>
To perform time-frequency analysis, we have imported the
preprocessed data into the FieldTrip format and applied Morlet
wavelets using the following code snippet:<br>
</p>
<p>```<br>
cfg = [];<br>
cfg.method = 'wavelet';<br>
cfg.output = 'pow';<br>
cfg.foi = 2:1:30;<br>
cfg.width = 3;<br>
cfg.pad ='nextpow2';<br>
cfg.toi = -1.5:0.02:2.28;<br>
ft_data_dev = ft_freqanalysis(cfg, ft_data_dev);<br>
```<br>
<br>
<br>
Our aim is to investigate power spectrum, phase, and
connectivity analysis in the context of language development,
particularly focusing on low frequencies ranging from 2 to 3 Hz
up to 30 Hz.<br>
<br>
However, I have encountered challenges in obtaining meaningful
data for low frequencies, especially at 2 and 3 Hz, where the
resulting values are NaN as well as in higher frequencies but
not over all time point. The resulting time frequency
representation has the the U shape described before in resources
mentioning boundary effect. I suspect that this issue may be
related to boundary effects, as our epochs may not adequately
capture the low-frequency oscillatory patterns.<br>
<br>
To me it seems like the cfg.width plus epoch length should not
have these strong boundary effects.<br>
<br>
Do you have any advise what I can change in order to get data in
the low frequencies? <br>
<br>
Best<br>
Erik S. Nickel<br>
<br>
<br>
**PS:**<br>
I am aware of these resources which discuss this topic:<br>
- <a class="moz-txt-link-freetext" href="https://www.fieldtriptoolbox.org/faq/why_does_my_tfr_contain_nans/">https://www.fieldtriptoolbox.org/faq/why_does_my_tfr_contain_nans/</a><br>
- <a class="moz-txt-link-freetext" href="https://www.fieldtriptoolbox.org/tutorial/cluster_permutation_freq/">https://www.fieldtriptoolbox.org/tutorial/cluster_permutation_freq/</a><br>
- <a class="moz-txt-link-freetext" href="https://mailman.science.ru.nl/pipermail/fieldtrip/2012-June/018208.html">https://mailman.science.ru.nl/pipermail/fieldtrip/2012-June/018208.html</a><br>
</p>
<pre class="moz-signature" cols="72">--
Erik Samuel Nickel
er/ihm (he/him)
Deutsch, English
M.Sc. Cognitive Science
</pre>
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