[Eeglablist] Extracting ASR weights and applying them later

[Makoto Miyakoshi]

Dear Andraz,

The short answer is no.

If any, if the input data's PSD is similar to the preemphasis filter i.e.
the 8th order Yule-Walker function that was heuristically determined by
Christian (the developer) as an inverse PSD of human EEG data (i.e. the
flattening filter, so to say), then ASR's artifact detection (according to
its own design) works most effectively. But this does not mean it helps the
algorithm per se.

> This is useful because the ICA solution can be improved with certain
preprocessing steps (high pass filtering at 1-2 Hz), but these
preprocessing steps don't necessarily have to be applied to the dataset to
which the ICA weights are applied.

I have words of warning for you. See my reply to Jan. Basically, I do not
recommend it. Remember, ICA's sensitivity is not uniform across all the
frequencies, but its sensitivity is (practically) proportional to the
amplitude. See my preliminary results from here
https://sccn.ucsd.edu/wiki/Makoto's_preprocessing_pipeline#Why_does_IC_rejection_increase_gamma_power.2C_or_why_is_an_IC_not_broadband-independent.3F_.28For_160.2C000_page_views.2C_05.2F10.2F2021_added.2C_06.2F27.2F2022_updated.29

Would you be surprised to hear that IC rejection generally INCREASES gamma
power? If you are surprised, read my Wiki article above. It is partly
related to what you are asking. Importantly, the lowest end of the power
spectrum usually has highest power, that's the point. If you are omitting
50 Hz and above for running ICA, practically it'll do no harm.

Makoto

On Tue, Aug 29, 2023 at 1:02 PM Andraž Matkovič via eeglablist <
eeglablist at sccn.ucsd.edu> wrote:

> Dear all,
> I have a question about ASR (Artifact Subspace Reconstruction). In ICA, it
> is possible to extract ICA weights and apply them to another data set. This
> is useful because the ICA solution can be improved with certain
> preprocessing steps (high pass filtering at 1-2 Hz), but these
> preprocessing steps don't necessarily have to be applied to the dataset to
> which the ICA weights are applied. For example, I can run ICA with a 1 Hz
> high-pass filter, but apply ICA weights to data with a 0.1 Hz high-pass
> filter. I am wondering if this is possible with ASR.
>
> Best regards,
> Andraž Matkovič
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