[FieldTrip] Edge effect/artifact in time-frequency representation

[MUSTAFA YAVUZ]

Dear Carlota Pages,

I'm not 100% sure about my expertise but I'll try to do a few comments. You
stated that whether this would be due to a preparation for a blink which
occurs after the end of the trial, however, as you also stated that this
effect disappears once you calculate the difference between conditions;
hene, it would be unlikely to be due to a random blink effect. I was
wondering whether this would be due to line noise since the script here
does not contain any cfg input for line noise removal (for
ft_preprocessing). Hope my limited knowledge does not cause any problem.

Best wishes,
Mustafa

PAGES PORTABELLA, CARLOTA MARIA <carlota.pages at upf.edu>, 14 Ara 2020 Pzt,
23:07 tarihinde şunu yazdı:

> Dear Fieldtrip community,
> I am Carlota Pagès, a Ph.D. candidate in the CBC of UPF (Barcelona).
> Currently, I'm exploring the neural oscillations of music unexpectedness.
>
> I have run time-frequency analysis on my EEG data via wavelet convolution
> and applied a dB baseline correction for my different conditions. However,
> when I plot the output, it appears some activity that (in my opinion) does
> not look as brain-related because of its high power values and might be
> masking the effects of interest (best seen in electrode Fz). When I
> calculate the difference between conditions, it disappears. Therefore, it
> is equally present in all conditions.
> I wondered whether it might be an artifact due to a preparation of blink
> (which happens right after the end of the trial) or an effect of the
> baseline correction (baselines are statistically equal across
> conditions). Please find the image and my script (for a single subject)
> below.
> Have any of you observed something similar and have a clue on what could
> be causing it? And if so, what would be a good way to correct it?
> Any help would be appreciated.
>
> cfg = [];
>
> cfg.demean = 'yes';
>
> data_demean = ft_preprocessing(cfg, data);
>
> % wavelet convolution
>
> cfg = [];
>
> cfg.method     = 'wavelet';
>
> cfg.output     = 'pow';
>
> cfg.foi        = 30:1:60;
>
> cfg.width      = 10;
>
> cfg.toi        = -0.7:0.03:1.2;
>
> cfg.pad =  2;
>
> cfg.trials     = data.trialinfo == 1;
>
> wavelet_cond1 = ft_freqanalysis(cfg, data_demean);
>
> % db normalization
>
> cfg = [];
>
> cfg.baseline = [-0.2 -0.05];
>
> cfg.baselinetype = 'db';
>
> wavelet_cond1_db = ft_freqbaseline(cfg, wavelet_cond1);
>
> % multiplot
>
> cfg = [];
>
> cfg.colorbar     = 'yes';
>
> cfg.channel = {'all', '-Fp1', '-Fp2'};
>
> cfg.showlabels = 'yes';
>
> cfg.layout = acticap32;
>
> figure; ft_multiplotTFR(cfg, wavelet_cond1_db);
>
>
> [image: multiplot.png]
>
>
>
>
>
> --
> Carlota Pagès
>
> PhD Student
> <https://www.upf.edu/web/lcc/entry/-/-/139611/adscripcion/carlota-pag%C3%A8s>
> Language & Comparative Cognition Group <https://www.upf.edu/web/lcc> l Center
> for Brain and Cognition <http://cbc.upf.edu/> l UPF
>
> *Office 24.326*
> *Mercè Rodoreda Building*
>
> *c\ Ramon Trias Fargas, 25-27
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> Barcelona
> <https://maps.google.com/?q=c%5C+Ramon+Trias+Fargas,+25-27+08005+Barcelona&entry=gmail&source=g>*
>
> _______________________________________________
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> https://doi.org/10.1371/journal.pcbi.1002202
>


-- 
*Mustafa Yavuz *

M.Sc. Candidate in Neuroscience

Department of Neuroscience
İstanbul University
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