[Eeglablist] ICA for ocular artifacts: split components?

[Cedric Cannard]

Hi,

Not sure about the abrupt interruption, but you can get this type of IC artifact if your data rank is low (due to channel interpolation and average reference for example), and if you don't use the GUI to launch ICA, it won't be detected I believe. I wonder if it's possible that you got some low rank in the time dimension (as opposed to channel), as you did some time interpolation.

Try launching ICA with the GUI, and/or with this command line to see if it solves the problem:

EEG = pop_runica(EEG, 'icatype', 'runica', 'pca', -1);


Cedric



‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Tuesday, May 4, 2021 1:12 AM, Agnese Zazio via eeglablist <eeglablist at sccn.ucsd.edu> wrote:

> Dear all,
>
> I am using ICA to correct for ocular movements in a TMS-EEG dataset with 74
> EEG channels, recorded with a sampling rate of 9600 Hz with
> online reference on FPz.
> Before ICA, I applied the following preprocessing steps: time interpolation
> around the TMS pulse (from 1 ms before to 2 ms after the TMS pulse), high
> pass filter at 1 Hz, downsampling at 4800 Hz, epoching from -200 to 500 ms
> after the TMS pulse (n=180 epochs), baseline correction (-100 -2 ms), SOUND
> algorithm for noise removal (Mutanen et al., NeuroImage 2018), artifact
> rejection. For ICA, I am using this code:
>
> EEG = pop_runica(EEG, 'chanind', [1: size(EEG.data,1)], 'interupt','on');
>
> When exploring the ICA components, In a few cases I found a 'strange'
> pattern: two components with a similar topography (but reversed in
> polarity) seem to reflect the same component but in distinct time-windows.
> As can be seen in the plot trials-by-time, the first component shows an
> ocular pattern up to about 250 ms, and the second component displays a
> similar pattern but from 250 ms on. What seems strange to me is that the
> temporal interruption at about 250 ms is very sharp. At this link (
> https://urldefense.com/v3/https://drive.google.com/file/d/1YiRjx4BPEPC6-NFySPbN-sNHwN6MmbLC/view?usp=sharing;!!Mih3wA!TSRqGkavVV4G_JOcKWIJFYOeQf68i2IF5NhBGlcT8W-_EeR9wq5KX0qMgBMeeuXsM_AxCw$ )
> you can see a figure which makes it much easier to understand the problem.
>
> Is anyone familiar with this issue?
> I'm using Matlab 2020b and eeglab v.2020.0.
>
> Thank you in advance.
>
> Best,
> Agnese
>
> ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
>
> Agnese Zazio, PhD
> Neurophysiology Lab
> IRCCS Centro San Giovanni di Dio Fatebenefratelli
> Via Pilastroni 4, 25125 Brescia, Italy
> Phone number: (+39) 0303501-596
> Site: https://urldefense.com/v3/http://www.cognitiveneuroscience.it;!!Mih3wA!TSRqGkavVV4G_JOcKWIJFYOeQf68i2IF5NhBGlcT8W-_EeR9wq5KX0qMgBMeeuVh3da2rQ$
>
> <https://urldefense.com/v3/http://www.cognitiveneuroscience.it/;!!Mih3wA!TSRqGkavVV4G_JOcKWIJFYOeQf68i2IF5NhBGlcT8W-_EeR9wq5KX0qMgBMeeuVKp4TURw$ >E-mail:
> agnese.zazio at gmail.com agnese.zazio at gmail.com
>
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