[FieldTrip] Calculating ERPs with tf_timelockbaseline

[Julian Keil]

Dear Luca,

have you plotted both datasets in one figure?

e.g.

figure
cfg = [];
cfg.layout = layout;
cfg.interactive = 'yes';
cfg.showoutline = 'yes';
ft_multiplotER(cfg, ERP, Color_C);

This way, you’ll see whether the two ERP traces actually overlap.
However, if the average of your baseline is indeed „close to zero“ as you state, then the baselinecorrection will not have a huge impact. In other words, if there is nothing to subtract, the ERP will not change.

Best,

Julian


> Am 09.04.2019 um 11:55 schrieb Luca Moretti <moretti.l1991 at gmail.com>:
> 
> Dear Julian,
> 
> I mean the second one: the signal does not change from Color_C to ERP. Inspecting Color_C as you suggested, it looks like there is a difference with ERP. However, ft_multiplotER seems to fail in plotting the ERP data. 
> At first I also thought that maybe I simply couldn't see the differences because the avarage was close to 0 in my baseline, but I tend to exclude this case as the figures are Always identical even when specifying different baseline periods, when plotting different electrodes, and when analyzing different subjects. 
> 
> Thank you again,
> Luca
> 
> Il giorno mar 9 apr 2019 alle ore 10:28 Julian Keil <julian.keil at gmail.com <mailto:julian.keil at gmail.com>> ha scritto:
> Dear Luca,
> 
> could you be a bit more precise in your description?
> By saying that "figure Always turn out the same for each electrode“, do you mean that the ERP is identical at each electrode?
> In that case, I suggest going back a step and checking whether the signal at each electrode is identical. That would indicate a problem earlier in your pipeline, e.g. that you overwrite the single electrodes with a common signal.
> 
> Or do you mean, that the signal does not change from Color_C to ERP? 
> In that case, I suggest inspecting Color_C in close detail, and computing the mean of the baseline interval by hand. If that value is close to zero, you can’t expect drastic changes from the baseline correction.
> 
> Hope that helps,
> 
> Julian
>  
> ________________
> Prof. Dr. Julian Keil
> 
> Biological Psychology
> Olshausenstrasse 62 - R. 306
> 24118 Kiel, Germany
> 
> +49 - 0431 - 880 - 4872
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> 
> 
>> Am 09.04.2019 um 10:11 schrieb Luca Moretti <moretti.l1991 at gmail.com <mailto:moretti.l1991 at gmail.com>>:
>> 
>> Dear Fieldtrippers,
>> 
>> I have a problem concerning the calculation of ERPs with ft_timelockbaseline. After I have preprocessed the data (re-referenced, filtered, cleaned from artifact), this is what I have done:
>> 
>> inputfile = (strcat('Subject_2_clean.mat'));
>> load (inputfile);
>> layout = 'easycapM1';
>> 
>> %% Calculating ERP
>> 
>> cfg = [];
>> cfg.trials = find(data_clean_2.trialinfo==60);
>> Color_C = ft_timelockanalysis(cfg, data_clean_2);
>> 
>> %% Plotting
>> 
>> cfg = [];
>> cfg.baseline = [-.3 0];
>> cfg.channel = {'all'};
>> cfg.parameter = 'avg';
>> ERP = ft_timelockbaseline(cfg, Color_C);
>> 
>> figure
>> cfg = [];
>> cfg.layout = layout;
>> cfg.interactive = 'yes';
>> cfg.showoutline = 'yes';
>> ft_multiplotER(cfg, ERP)
>> 
>> %%
>> 
>> My problem is that it doesn't matter what kind of baseline period I am chosing, the figure Always turn out the same for each electrode. I have even tried to set the baseline to the Whole trial period, but the figure I get from plotting individual channels from the multiplot is Always the same.
>> 
>> Can someone find something wrong with my code?
>> 
>> Many thanks!
>> Luca
>> 
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