[FieldTrip] many ICA components looking the same

Stephen Politzer-Ahles stephen.politzer-ahles at ling-phil.ox.ac.uk
Thu Oct 29 07:31:19 CET 2015

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?


Stephen Politzer-Ahles
University of Oxford
Language and Brain Lab, Faculty of Linguistics, Phonetics & Philology

> Message: 5
> Date: Wed, 28 Oct 2015 20:44:26 -0700
> From: Vit?ria Piai <v.piai.research at gmail.com>
> To: FieldTrip discussion list <fieldtrip at science.ru.nl>
> Subject: [FieldTrip] many ICA components looking the same
> Message-ID: <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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