[FieldTrip] question about automatic artefact rejection
e.spaak at donders.ru.nl
Tue Feb 18 11:45:03 CET 2020
Since there is no statistical test involved, I see no problems with
computing a z-score here. Think of it more as bringing the data into a
sensible range and allowing yourself to forget about details like
measurement unit etc. You could also not do the z-transform, and
simply specify a threshold based on raw amplitude, this would be
equivalent (but might make it potentially more difficult to come up
with a good threshold).
On Tue, 18 Feb 2020 at 09:47, De Meyer, Kris <kris.de_meyer at kcl.ac.uk> wrote:
> Dear Fieldtrippers,
> In ft_artifact_muscle, an EEG signal is first filtered - usually with a bandpass filter with cutoff frequencies of [110,140]. The documentation then says that the hilbert envelope is calculated, after which the envelope values are z-transformed before they are thresholded.
> However, is this sound? Whereas the actual filtered EEG values (the result of the bandpass filter) are usually normally distributed, the hilbert envelope values are far from.
> What is the rationale for calculating the z-transform of a non-Gaussian distribution? Doesn't that introduce problems?
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