[Eeglablist] ICA for ocular artifacts: split components?

Scott Makeig smakeig at gmail.com
Wed May 5 11:25:18 PDT 2021


You should try plotting erpimage plots of the channel voltages in the
peri-ocular channels.  What do the data, as input to ICA decomposition,
look like?

Scott Makeig

On Wed, May 5, 2021 at 1:23 PM 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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-- 
Scott Makeig, Research Scientist and Director, Swartz Center for
Computational Neuroscience, Institute for Neural Computation, University of
California San Diego, La Jolla CA 92093-0559, http://sccn.ucsd.edu/~scott


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