WIP: Add scalp coupling index for NIRS data

[rob-luke]

Reference issue

Discussed in #7057

What does this implement/fix?

This is the standard method for determining a good/bad channel in NIRS literature. It measures the quality of the connection between the sensor and the scalp. This is done by looking for the presence of heart rate in the nirs signal across the different wavelength signals. The data is band pass filtered to retain only the heart rate, then the correlation between signals is computed. See [1]

Additional information

I haven't added to the current fNIRS tutorial, mainly because I went to great lengths to get clean data for that recording, so the SCI doesn't show much.

I also moved two function from the beer lambert law file to the general nirs file, as these are also used in this function.

[1] Pollonini, Luca, et al. "Auditory cortex activation to natural
speech and simulated cochlear implant speech measured with functional
near infrared spectroscopy." Hearing research 309 (2014): 84-93.

[codecov]

Codecov Report

Merging #7215 into master will increase coverage by 0.07%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #7215      +/-   ##
==========================================
+ Coverage   89.82%   89.89%   +0.07%     
==========================================
  Files         447      449       +2     
  Lines       80694    79960     -734     
  Branches    12876    12876              
==========================================
- Hits        72482    71881     -601     
+ Misses       5385     5244     -141     
- Partials     2827     2835       +8     

[rob-luke]

@larsoner could you please review this PR. Thanks

[larsoner]

I haven't added to the current fNIRS tutorial, mainly because I went to great lengths to get clean data for that recording, so the SCI doesn't show much.

Doesn't hurt to add it even if it is a no-op for these data. I would write something like this in the tutorial:

# Mark bad channels based on coupling index
# -----------------------------------------
# Next we run XXX method, which does YYY. These data are pretty
# clean, so the method will yield no # bad channels:

...

[larsoner]

LGTM, just some ideas for cleanups

[rob-luke]

Thanks for the feedback @larsoner. I think I have addressed your issues (and raised a few questions above). Could you please review again.

[rob-luke]

@larsoner I'm not sure why these windows builds are failing. Could you please help me understand the build errors? Thanks

[larsoner]

@rob-luke we are having some random errors that hopefully will be fixed soon by #7295. If this is good to go from your end let me know and I'll take a look

[rob-luke]

@larsoner, yes I think I have addressed all your previous comments. Could you please review again.

[larsoner]

Thanks @rob-luke !