[FieldTrip] No mtmconvol on data with partial nans

Stephen Whitmarsh stephen.whitmarsh at gmail.com
Wed May 25 15:26:25 CEST 2016

Hi FieldTrippers,

I hope someone can help me with the following.

My problem is that I like to maintain my original rpt/chan/time/freq size after artefact rejection based on the time series data, i.e. to have the same dimensions of the TFR as if I did not reject data. This is for reasons of bookkeeping between different types of channels that are processed differently throughout my analysis.

What works well is to detect artifacts in the data and replace those intervals with nans using ft_rejectartifact, with cfg.reject = 'nan'. So far this is perfect for the approach I had in mind.

However, ft_freqanalysis (method = 'mtmconvol') outputs whole trials as nans whenever a (small) period has nans. What I would need - and in fact expect - is that only those time/frequency windows that have (one or more) nan values will output nan, while the rest should merrily go round giving power values. After all, the data is there.

It is unclear to me whether this is expected behaviour or not. I might be making a mistake but some simple tests replicated this behaviour.

Is there a solution that still allows me to end up with a rpt/chan/time/freq representation of the same size as when i would not have rejected artifacts?

The only other FieldTrip-like option I can think of is to use ft_rejectartifact with method = 'partial', do the freqanalysis on trial parts, and somehow glue the separate trial parts together again afterwards. But I really don't want to go in that direction.

In the end I'm afraid I don't understand the core of ft_specest_mtmconvol enough to see where I could hack it. I hope some of you might be able to help.

Best wishes,

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