[Eeglablist] multiple runs/parts of the same paradigm - when to concatenate

Janosch Linkersdörfer notes4januz at gmail.com
Wed Apr 9 01:15:51 PDT 2014


Hi Steve and Iman,

thank you both for your detailed answers and advice! 

Am 09.04.2014 um 10:06 schrieb Stephen Politzer-Ahles <politzerahless at gmail.com>:

> Hi Janosch,
> 
> Actually I had misread your previous message.... in your case it is probably fine to run ICA on the concatenated data, since the cap wasn't taken off in between blocks. The time when you'd want to do ICA before concatenation is when the cap was taken off in between (e.g., if you divided experimental sessions over two different days), because small differences in the cap's placement can cause the same physiological "component" to appear as two different ICs. But it sounds like your blocks are from the same recording 'session', with the cap staying on the whole time, so this is probably not an issue.

Yes, that's the scenario.

> Since that's not an issue, then like Iman said, it's ideal to have as many samples as possible for your ICA.

Great, I will concatenate before then.

All the best,

Janosch

> 
> Best,
> STeve
> 
> 
> 
> Stephen Politzer-Ahles
> New York University, Abu Dhabi
> Neuroscience of Language Lab
> http://www.nyu.edu/projects/politzer-ahles/
> 
> 
> On Wed, Apr 9, 2014 at 10:32 AM, Janosch Linkersdörfer <notes4januz at gmail.com> wrote:
> Hi Steve and Iman,
> 
> thank you very much for your answers. I indeed plan on using ICA for preprocessing. As you propose different strategies (concatenating before vs. after ICA), could you please elaborate on why it is or is not appropriate. Could you maybe point me to some literature?
> 
> Thanks a lot,
> 
> Janosch
> 
> >> I would prefer to concatenate all and then do ICA and etc , especially if your data sampleas are few...
> >> Best
> >> Iman
> >>
> >> ============================================
> >> Iman M.Rezazadeh, Ph.D , M.Sc., B.Sc.
> >> Semel Institute for Neuroscience and Human Behavior
> >> University of California, Los Angeles (UCLA)
> >> Am 09.04.2014 um 06:22 schrieb Stephen Politzer-Ahles <politzerahless at gmail.com>:
> 
> > Hi Janosch,
> >
> > This depends on what things you are doing during preprocessing. For example, if you are doing ICA, then this should be done before concatenation. For many other steps, like epoching and filtering, this doesn't really matter (although a filter might take longer to run on the concatenated than the un-concatenated data, since it would have to deal with the boundary).
> >
> > Best,
> > Steve
> >
> >
> >
> > Stephen Politzer-Ahles
> > New York University, Abu Dhabi
> > Neuroscience of Language Lab
> > http://www.nyu.edu/projects/politzer-ahles/
> >
> >
> > On Tue, Apr 8, 2014 at 6:18 PM, Janosch Linkersdörfer <notes4januz at gmail.com> wrote:
> > Hi all,
> >
> > I am writing a script to import EGI .mff data into eeglab and save them as .set files for further (pre)processing.
> >
> > One of the paradigms is split into two runs. For another paradigm that should have been run in one go, for some of the participants there are two files, because the participants (children) had to go to the bathroom in between blocks.
> >
> > In the script I look whether multiple files for one paradigm exist, and if so concatenate them using pop_mergeset.
> >
> > I now wonder whether this is correct or whether I instead have to preprocess each file individually and later concatenate them before (or after) epoching.
> >
> > It would be great if you could help me!
> >
> > Thanks,
> >
> > J
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> 
> 



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