I can easily reproduce the reports you're providing here (concatenate vs average). Unfortunately, estimating coherence from short trials is complicated:
- concatenated: signal full of discontinuities, and therefore not adapted for this kind of analysis
- averaged: averaging many poorly-estimated coherence values
@eflorin @Sylvain @hossein27en @leahy @pantazis @Marc.Lalancette
Has this concatenation approach ever been published anywhere?
This seems to give very low imaginary coherence values, and very different from the averaging approach. Do we have any formal proof that this is to be recommended?
Previous posts discussed this topic, with no clear references either:
- Concatenating data, how is it done?
- Coherence on trials or concatenate file
- Imaginary Coherency Output - Time Average - #2 by Francois
While testing this, I found some issues in the icohere2019 computation:
-
https://github.com/brainstorm-tools/brainstorm3/issues/363
And in the spectrum display of the coherence results: - https://github.com/brainstorm-tools/brainstorm3/commit/d94cce1d6d3ccbc41b9ad84275cca00ba59952ca
- https://github.com/brainstorm-tools/brainstorm3/pull/362