[Eeglablist] Fwd: Question: Single Trial ICA Component Activations

[Iversen, John]

John,

The answer is 'yes'.

For epoched data, EEG.data typically has shape [channel x sample x epoch], so, for epoch ‘e'

EEG.icaact(:,:,e) = (EEG.icaweights*EEG.icasphere)*EEG.data(EEG.icachansind,:,e)


The ICA solution does not vary with time, so the same unmixing solution is applied to every time point.



If you want to get into it, look through e.g. eeg_checkset.m, which shows how EEG.data is reshaped into a 2-d matrix [channel x (samples*epochs)] for saving:

reshape(EEG.data, EEG.nbchan,  EEG.pnts*EEG.trials);

and then when reloaded, ICA activations are recomputed on this 2-d matrix, and then put back into [channel x sample x epoch] shape:

EEG.icaact = (EEG.icaweights*EEG.icasphere)*EEG.data(EEG.icachansind,:); % automatically does single or double

EEG.icaact    = reshape( EEG.icaact, size(EEG.icaact,1), EEG.pnts, EEG.trials);


John


John R. Iversen, PhD
University of California, San Diego
Swartz Center for Computational Neuroscience
Institute for Neural Computation
9500 Gilman Dr #0559
La Jolla, CA 92093
jiversen at ucsd.edu<mailto:jiversen at ucsd.edu>



On Aug 1, 2018, at 9:18 AM, John Myers <john.myers at my.utsa.edu<mailto:john.myers at my.utsa.edu>> wrote:

Hello Everyone!

I'm writing to ask how to generate ICA component activations (EEG.icaact) for single trials using the data structures in EEGLAB.

I know that EEG.icaact = (EEG.icaweights*EEG.icasphere)*EEG.data. I'm wondering if this formula can be used to transform a single trial of EEG data into component activations.

Concretely, my quesiton is, "Can I compute an IC activation for a single trial using the (EEG.icaweights*EEG.icasphere)*EEG.(single trial data)? If not, how can I do this using EEGLAB's structures.

Best wishes,

--
John Myers, M.S.
PhD Student
Cognitive Neuroscience Lab
UTSA
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