[FieldTrip] many ICA components looking the same

[Vitória Piai]

hi Steve,

Thanks, sounds like a very reasonable explanation.
I'm wondering whether I could use Arjen's correction for head movement 
prior to ICA decomposition, but I can imagine there would be problems 
with doing the regression first... I'll ask Arjen what he thinks and 
post it here - if he doesn't see this before I see him again - but I'd 
be curious to hear what you think as well.

Thanks a lot!
Vitoria

On 10/28/2015 11:31 PM, Stephen Politzer-Ahles wrote:
> Hello Vitoria,
>
> I'm not sure, but one of my guesses would be head movement. That is to 
> say, if the participant moves her head an inch (for example) then the 
> same type of activity is going to start appearing on different 
> sensors, and if that movement isn't corrected for then you can indeed 
> start seeing what looks like many copies of the same component. (If 
> you've done EEG, this is the same thing that happens when, for 
> example, you bring the same participant back for multiple sessions on 
> separate days and concatenate the datasets together, but didn't put 
> the cap on on exactly the same place each time.) Do you have marker 
> measurements you can use to at least check how much the head was 
> moving, and perhaps to correct for movements over the course of the 
> session?
>
> Best,
> Steve
>
>
>
> ---
> Stephen Politzer-Ahles
> University of Oxford
> Language and Brain Lab, Faculty of Linguistics, Phonetics & Philology
> http://users.ox.ac.uk/~cpgl0080/ <http://users.ox.ac.uk/%7Ecpgl0080/>
>
>     Message: 5
>     Date: Wed, 28 Oct 2015 20:44:26 -0700
>     From: Vit?ria Piai <v.piai.research at gmail.com
>     <mailto:v.piai.research at gmail.com>>
>     To: FieldTrip discussion list <fieldtrip at science.ru.nl
>     <mailto:fieldtrip at science.ru.nl>>
>     Subject: [FieldTrip] many ICA components looking the same
>     Message-ID: <5631961A.1050507 at gmail.com
>     <mailto:5631961A.1050507 at gmail.com>>
>     Content-Type: text/plain; charset="utf-8"; Format="flowed"
>
>     Hi everyone,
>
>     I'm running ICA (cfg.method = 'runica') on CTF data with 274
>     sensors. I
>     was restricting my decomposition to 80 components at first, and it
>     worked well for all previous patients.
>     Somehow, for this particular patient, many of the components have
>     similar topography (I'm only showing till 42 below but the similarity
>     continues for more components). Has anyone ever seen this before?
>     If I look at the time course of these components, not all of them are
>     clear eye-movements, but according to the topography, you'd think
>     they are.
>     Any thoughts, like either changing the method or rejecting only those
>     components whose time courses clearly indicate eye movements and keep
>     other components despite their topographies?
>
>     Thanks,
>     Vitoria
>
>
>
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