[Eeglablist] All red or blue ICA

[Luca Pion-Tonachini]

I would just like to note that in the examples I have seen, these 
components are not limited to "line noise" components.

Luca

On 04/06/2017 11:49 AM, Jason Palmer wrote:
>
> Hi Julia,
>
> I think Luca is probably right, the “flat” components are usually line 
> noise (common mode). You can verify that by looking at the component 
> activation (using plot component activations) corresponding to that 
> map. It should be sinusoidal, with 50 or 60 cycles per second. Also 
> the associated spectrum should have a huge peak at 50 or 60 Hz.
>
> The appearance of line noise maps depends on the recording 
> environment, and the referencing. Average referencing will usually 
> leave some line noise, and then if ICA separates out the residual line 
> noise, the map be compact rather than flat. In my experience, I often 
> see line noise maps that look like frontal midline (brain component) 
> maps, but are actually residual line noise.
>
> Looking at the component activation is usually a pretty good way to 
> determine whether a component is a “good” brain component, or “noise” 
> or artifact.
>
> Best,
>
> Jason
>
> *From:*eeglablist-bounces at sccn.ucsd.edu 
> [mailto:eeglablist-bounces at sccn.ucsd.edu] *On Behalf Of *Luca 
> Pion-Tonachini
> *Sent:* Thursday, April 06, 2017 7:20 AM
> *To:* eeglablist at sccn.ucsd.edu
> *Subject:* Re: [Eeglablist] All red or blue ICA
>
> Hi Julia,
>
> I've seen the before as well and my personal theory is that they are 
> due to common mode noise (though I don't have direct proof). If you 
> change your data to using a common average reference, I think they 
> should go away. That would also explain why your data looks cleaner 
> without them, as you are essentially removing the common mode noise 
> (albeit in an roundabout way).
>
> Luca
>
> On 04/05/2017 08:24 AM, Julia Basso wrote:
>
>     Dear all,
>
>     I have a 20 channel EEG system and after cleaning the data by
>     first conducting a band pass filter than cleaning epoched data by
>     visual inspection, I am running ICA to detect and remove eye
>     blinks and eye movements.
>
>     My question is in regards to ICs that are distinctly all blue or
>     all red.  My instinct is to remove these ICs (and when I do, the
>     data looks cleaner)- but I wanted to get your opinion.  What does
>     this type of IC indicate?  Is it merely noise in the system?
>
>     Best,
>
>     Julia
>
>     -- 
>
>     /Julia C. Basso, PhD, CYT/
>
>     /Post-doctoral Research Associate/
>
>     /New York University/
>
>     /Center for Neural Science/
>
>     /Suzuki Laboratory/
>
>     /4 Washington Place, Room 809/
>
>     /New York, NY  10003/
>
>     /(212) 998-3969/
>
>     www.juliabasso.com <http://www.juliabasso.com>
>
>     /www.suzukilab.com <http://www.suzukilab.com>/
>
>
>
>
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