evaluating ics - university of california, san diegoapplying ica weights to eeg data eeg.icaweights...
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![Page 1: Evaluating ICs - University of California, San DiegoApplying ICA weights to EEG data EEG.icaweights * EEG.icasphere EEG.data EEG.icaact matrix multiplication els channels frames els](https://reader033.vdocuments.us/reader033/viewer/2022043022/5f3dd2ec5ede6706b316d782/html5/thumbnails/1.jpg)
Evaluating ICs
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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ICA weights in EEG structure
* *
EEG.icawinv = inv(EEG.icaweights * EEG.icasphere)
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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Applying ICA weights to EEG data
EEG.icaweights
*
EEG.icasphere
EEG.data
EEG.icaact
matrix
multiplication
ch
an
nels
channels
frames
ch
an
nels
ch
an
nels
frames
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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Applying ICA weights to EEG data
Note: .wts and .sph not saved as separate files by EEGLAB,
you must save them yourself:
floatwrite(EEG.icaweights,'C:\MyDirectory\ICA.wts');
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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Applying ICA weights to EEG data
Same for sphering matrix
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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Evaluating ICs
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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Plot ICA scalp maps
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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Single-dipole projections
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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Compare 'good' and 'bad' scalp maps
chaotic gradients
no clear patterns
INconsistent with single dipoles
smooth gradients
concentric rings (when radial)
consistent with single dipoles
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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Evaluating ICs
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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Scroll component activities
Time periods that are not independent across ICs
should be removed and ICA run again for better decomposition
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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Plot component power
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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Plot component power
6
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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Component ERPs
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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Component ERP image
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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ERP Image basics
Trial 1
Trial 2
Trial 3
Trial 4
ERP Image
by default, sorted by
time-on-task
(1st trial, 2nd trial, ...)
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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ERP Image basics Trial 1:
Trial 2:
.
.
.
+
-
+
-
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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ERP Images: smoothing across trials
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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Evaluating ICs
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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Plot ICA component properties
Trial 4
Trial 1
Trial 2
Trial 3
ERP Image
Does not require
epoched dataset,
but ERP image
will be less
informative
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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Reviewing component properties
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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Component scalp maps/properties
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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Eye blink component
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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Eye blink component
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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Lateral eye movement
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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Muscle
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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Brain ICs
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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more brain ICs
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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Pulse artifacts
periodic spiking behavior
Often 2 peaks
between 5 and 10 Hz
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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Exercise
• ALL
- Load stern.set (continuous data, contains ICA weights)
• Novice
- Plot IC scalp maps
- Scroll the IC activations and compare to channel data scroll
- Identify “artifact” ICs
> How can you be sure it is an artifact?
• Intermediate / Advanced
- Practice saving EEG.icaweights and EEG.icasphere as .wts
and .sph files and re-apply the weights again to stern.set
- Plot IC power, try different parameters from the GUI
- From supplementary material, try automatic data epoch
rejection.
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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Supplementary lessons
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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Auto-reject data epochs
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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Reject data epochs
visual
inspection
probability
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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Reject data epochs
Number of epochs
above threshold
indicated here
32 Start by clicking
Calculate:
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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Reject or retain marked epochs
32
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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Reject marked epochs
>> EEG = pop_jointprob(EEG,1,[1:70],5,5,0,0);
>> EEG = pop_rejepoch(EEG,find(EEG.reject.rejglobal),0);
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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Select epochs
>> EEG = pop_selectevent(EEG,'type',{‘in'},...
'deleteevents', 'off','deleteepochs','on');
>> [ALLEEG EEG CURRENTSET] = pop_newset(ALLEEG,EEG,4,...
'setname','faces only epochs'); EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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Select epochs with specific events
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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Repeat for ‘out-of-set’ responses
Save without overwriting and go back to all epochs
Repeat process for ‘out’ trials
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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Separate datasets with different conditions
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components
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Explanation of "sphering"
For more explanation, see:
http://sccn.ucsd.edu/~arno/indexica.html
and http://sccn.ucsd.edu/wiki/Linear_Representations_and_Basis_Vectors
"Sphering":
Remove channel
correlations
Equal variance
on both (all) axes
Original data
Sphered data
Like ICA, sphering is also a linear
operation, so re-projecting to original
space simply requires multiplying
with weight matrix
EEGLAB Workshop, June 16-18, 2012, Beijing, China: Julie Onton – Evaluating ICA Components