[Eeglablist] Clarification Needed on EEG Analysis in EEGLAB

[Scott Makeig]

Marjan,

As the current spread from effective EEG sources (partially synchronized
cortical area, eyeballs, scalp/neck muscle, ambient line noise, ...) to
scalp channels are spatially broad, scalp channel signals sum contributions
of ~all effective sources to varying extents.  The effective source
waveforms themselves, e.g. as unmixed by well-applied ICA decomposition,
are NON-Gaussian - but their linear mixtures (e.g., the scalp channel
signals themselves) tend to be more Gaussian (as mathematically probable).
In sum, EEG  scalp channels are poor/inefficient spatial filters, each a
mixture of activities of >>1 effective sources, and are thus only vaguely
related to brain activity in any effective source area (emergent areas of
local local field synchrony).

Scott Makeig

On Sun, Jan 26, 2025 at 11:33 AM m za via eeglablist <
eeglablist at sccn.ucsd.edu> wrote:

> Dear all,
>
>  I hope this message finds you well. I am reaching out to seek your
> guidance on two issues I am currently facing regarding EEG analysis using
> EEGLAB.
>
> First, I have a question regarding the channel statistics section. When we
> assess channel normality, I understand that if the channel deviates
> significantly from Gaussian distribution, we consider it non-Gaussian and,
> thus, not EEG. However, I would like to clarify the general assumption we
> make about data distribution when we do not have any distribution data,
> specifically whether we can safely assume it to be normal.
>
> Secondly, regarding the SIFT software, I am concerned about the
> implications of not meeting the white noise criterion. Would this pose a
> problem, or can the issue be mitigated using surrogate criteria to
> eliminate invalid connectivity?
>
> I would greatly appreciate your insights on these matters.
>
> Thank you for your help!
>
> Best regards,
>
> Marjan
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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