[Eeglablist] Warning: change STUDY design

[Jet Zoon]

Thank you for the clarification.

Op wo 18 jul. 2018 om 20:38 schreef Makoto Miyakoshi <mmiyakoshi at ucsd.edu>:

> Dear Jet,
>
> > ICA has been performed for the two datasets separately.
>
> Good.
> The basic rule is that removing an electrode cap and new ICA is necessary,
> unless you can replicate the original cap/electrode location with
> sub-millimeter precision.
>
> https://sccn.ucsd.edu/wiki/Makoto's_preprocessing_pipeline#General_tips_for_performing_ICA_.2806.2F26.2F2018_updated.29
>
> > I understand that that is why I get to see the warning I mentioned.
>
> There is EEGLAB 'session' which, I believe, is supposed to use 'same
> subject but different capping'. However, I often simply regard the same
> subject different sessions as different subjects. This way you can avoid
> troubles you experienced.
>
> > Should this be possible?
>
> No. You can't 'merge' different sessions (i.e., different capping) from
> the same subject. EEGLAB's 'merge' only works if and only if ICA-related
> matrices are shared and identical (i.e.,  paired t-test is possible).
>
> > However, since the two datasets have been aqcuired on two separate days
> I understand that ICA analyses should be performed on the datasets
> separately.
>
> You should treat them as if the data were from different subjects (i.e.,
> you have to use two-sample t-test)
>
> Makoto
>
> On Tue, Jul 17, 2018 at 10:34 PM Jet Zoon <jetzoon at gmail.com> wrote:
>
>> Dear eeglablist,
>>
>> In using eeglab to perform analyses for a study with a rather complex
>> design I ran into the following warning: Warning: ***** change STUDY design
>> as it combines datasets with different ICA decompositions.
>>
>> A short description of the design:
>> testday 1: participants receive a high-energy savoury meal
>> testday 2: participants receive a high-energy sweet meal
>> Before and after meal intake we measured neural responses (using EEG) to
>> visual and olfactory stimuli of the following categories:
>> High-energy savoury food
>> High-energy sweet food
>> Low-energy savoury food
>> Low-energy sweet food
>> Non-food
>> Baseline (no product/no odour)
>> Each stimulus category was presented 18 times before and 18 times after
>> meal intake.
>>
>> To keep the statistical power as high as possible, with the limited
>> amount of items we presented, I would like to combine stimulus categories
>> between the two test sessions. I think that it is best to end up with the
>> stimulus categories: fully congruent (between meal and stimulus: e.g.
>> High-energy sweet meal - high-energy sweet odour), taste congruent, energy
>> congruent, not congruent, non-food and baseline.
>>
>> I now included data from two sessions on two separate days in the study
>> dataset. ICA has been performed for the two datasets separately. I
>> understand that that is why I get to see the warning I mentioned. However,
>> in contrast to what is mentioned in an earlier conversation on this topic (
>> https://sccn.ucsd.edu/pipermail/eeglablist/2011/003669.html), I can run
>> the analyses and get my results.
>>
>> Should this be possible? Can I just interpret the results as usual or
>> does combining items from two datasets provide invalid results? If so, is
>> there another option to combine the items from the two datasets? In the
>> message I referred to, it is suggested to only merge sessions with the same
>> ICA decomposition. However, since the two datasets have been aqcuired on
>> two separate days I understand that ICA analyses should be performed on the
>> datasets separately.
>>
>> I really appreciate your help in resolving this problem.
>>
>> Kind regards,
>> Jet Zoon
>>
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>
>
> --
> Makoto Miyakoshi
> Swartz Center for Computational Neuroscience
> Institute for Neural Computation, University of California San Diego
>
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