How to build an adjacency matrix for spatio-temporal cluster tests?

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Hello,

I am comparing the time-frequency matrices (n_freqs, n_times) between two conditions using mne.stats.spatio_temporal_cluster_1samp_test.

If I understand correctly setting the adjacency parameter to None (default) will connect adjacent neighbors in the time dimension (horizontal). I would like to consider adjacent neighbors in both the frequency (vertical) and time (horizontal) dimensions.

Is there an example I could follow to set up such an adjacency matrix?

Many thanks!

Ana P

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Hello @anapesq, if the input data has the shape (observations, times, frequencies), passing adjacency=None should do exactly what you want and form clusters across immediately neighboring time and frequency bins. Clusters are always implicitly formed over neighboring time points.

Best wishes,
Richard

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Hello @richard!

Thank you for the quick reply and clarification.
Do you know how I would have to set-up the adjacency if I wished to check not only the immediately neighboring time and frequency bins (next cells) but also the bins at a distance of two cells?
Meaning, how could I expand what is considered a neighboring cell.

Thank you!

Ana P

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I’m sure @sappelhoff is now in a good position to help here — he just reworked a big chunk of the clustering documentation :grin:

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5

Do you mean you don’t have “channels” as a dimension? If your data is really just observations * n_freqs * n_times, then mne.stats.spatio_temporal_cluster_1samp_test is the wrong test to choose, see the docstring:

This function provides a convenient wrapper for mne.stats.permutation_cluster_1samp_test() , for use with data organized in the form (observations × time × space).

I think I would rather advise you to use: mne.stats.permutation_cluster_1samp_test

You could have a look at the max_step parameter in the cluster permutation functions. However I haven’t looked into the source code for that, and the parameter description makes me think that:

  1. this param only works when you specify adjacency for channels as obtained by mne.channels.find_ch_adjacency
  2. this param only works for the 2nd dimension of the input data … and not as you’d like to have it, for several input dimensions

So overall I don’t think this is possible right now, but it sounds like a very reasonable feature request to me to expand what max_step can do.

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Dear @sappelhoff,

Thank you for your quick and informative reply.

I re-run the analysis using the suggested mne.stats.permutation_cluster_1samp_test() and the results are the same as when using ‘mne.stats.spatio_temporal_cluster_1samp_test()’. Possibly the later function (which is not the preferred as you suggest) adapts to an input without the channel dimension.

I will look into how to request mne features.

Many thanks!

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