[FieldTrip] Clarification on plotting WPLI

[Peter Lyons]

Hello Everyone,

I have a question regarding the interpretation of negative values in the
debiased wPLI. Although the reference page on the debiased wPLI notes that
estimates are computed by squaring the wPLI values, I and others have
noticed that some of the values in the debiased wPLI spectrum are negative.
How should these negative values be interpreted in reference to 0?

To view the results of the debiased wPLI connectivity analysis
(ft_connectivity analysis with cfg.method = 'wpli_debiased'), I've been
using the ft_topoplotER function. However, I'm concerned that the default
scaling (zlim = 'maxmin') of the plot does not seem to register the
negative values in the debiased wPLI spectrum. That is, the negative values
are not being plotted. It is curious, however, that the ft_topoplotER
does register the negative values in the *non-debiased *wPLI spectrum.

Is there a reason why the ft_topoplotER function is treating the negative
values from the debiased vs. non-debiased wPLI spectrums differently? Is
there perhaps a more appropriate plotting function I should be using to
view the debiased wPLI output?

I would greatly appreciate any guidance in this.

Thank you!

Peter
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