[FieldTrip] many ICA components looking the same

[Vitoria Piai]

Hi all,

Just adding this info for the sake of completeness. Thanks, Arjen, for 
clarifying it!

As I suspected, it's *really* not a good idea to use ft_regressconfound 
before ICA. In fact, this function should be used only at the very 
latest stages of your analysis, either just before doing stats, or by 
incorporating the approach in the stats itself.

Vitória

On 10/29/2015 11:01 AM, Vitória Piai wrote:
> 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>
>>     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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