[Eeglablist] Combining data from different tasks within the same EEG session for ICA

[Stephen Politzer-Ahles]

Hi Neil,

It seems to me like it would in fact be better to submit all the data to
the same ICA decomposition, especially if you plan on comparing them, since
you would want any differences you do observe to be based on the tasks
themselves, rather than differences you introduced by running different
compositions (and perhaps removing different components). Indeed, in most
ERP research comparing different conditions, one would still expect
underlying neural activity to show [slight] differences between conditions,
but trials of the different conditions are still usually combined in the
same ICA decomposition. See the following message for more discussion of
this (as well as discussion of how you could go about the analysis using
separate ICAs): http://sccn.ucsd.edu/pipermail/eeglablist/2011/003694.html

Also, as an aside, you asked if it matters whether the epochs are different
lengths; I'm not sure EEGLAB can handle epochs of differing lengths anyway?
To do that, you may need to use an additional plugin, or try Fieldtrip, or
concatenate the epochs to look like continuous data (which may raise other
issues; this has been discussed on the list before, but I don't recall the
details).

Best,
Steve




Stephen Politzer-Ahles
New York University, Abu Dhabi
Neuroscience of Language Lab
http://www.nyu.edu/projects/politzer-ahles/

On Fri, May 29, 2015 at 7:43 AM, Neil Bailey <neil.bailey at monash.edu> wrote:

> Hi all
>
> Does anyone have a good sense on whether it would be valid to combine
> epochs from the same EEG session, but different tasks in order to maximise
> data for ICA decomposition?
>
> I'm aware that feeding more data into the ICA gets better results, and the
> data from the different tasks will have similar artifacts to be removed
> (eye movement, muscle, line noise). However, the underlying neural activity
> will differ between the tasks (for example the Sternberg working memory
> task generates a large amount of posterior alpha, while the Go/Nogo task
> does not, but does generate a large N2 and P3 component).
>
> Will the differences in the underlying neural activity between tasks
> negatively affect the results of the ICA if activity from different tasks
> is combined? And will it matter if the epochs from different tasks are of
> different lengths?
>
> Kind regards,
>
> --
> Neil Bailey (PhD)
> Monash Alfred Psychiatry Research Centre
> Neil.Bailey at Monash.edu
> (03) 9076 5032
>
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