[Eeglablist] ICA suggests weirdly low rank

[Ivonne Weyers]

Dear list members,

I am experiencing some issues running pop_runica, namely that it 
produces weirdly *low* rank.

I have a 27-channel infant dataset recorded with a single channel 
reference (Fz), for which I perform the following steps before running 
ICA: filter, remove bad channels, interpolate, re-reference to average 
reference and adding Fz back to the data, epochize (this does not reduce 
the amount of data by much, just truncates the continuous data), reject 
only extremely large artifacts.

I understand from previous discussions as well as the papers on this 
issue that my data becomes rank deficient by n if I interpolate n 
channels. (Is rank reduced further by -1 due to average re-ferencing 
even if the original reference is added back to the data?) When I run 
pop_runica on a 27 channel data set in which channels have been 
interpolated, however, eeglab returns a substantially lower rank, e.g. 
22 when two channels have been interpolated (which should be 25; or 24 
if average referencing reduces futher).

 From what I have read in the mailing list, most people experience the 
opposite, i.e. rank() failing to identify rank deficiency, but I haven't 
found anything on weirdly low rank. Does anyone have an idea what may be 
causing this?

Also, I am unsure whether I should "force" it to compute 25 ICs using 
the gui or the 'pca' option, could this be detremental to ICA results?

I would appreciate any ideas on this, also let me know if I failed to 
include any details on the data.

Thank you & best,

Ivonne

-- 



*Dr. rer. nat. Ivonne Weyers (she/her)*
Psycholinguistics Group
Institute of Linguistics
University of Vienna
Sensengasse 3A, Room 06.12
1090 Wien

ivonne.weyers at univie.ac.at