evaluating ica components...10 12 10 12 .01 0 'ampsort' , [0 0 10 12] same data: sorted by...
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Evaluating ICA components
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Eye blink correction (remove IC)
Identify eye-blink
components:
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
IC rejection/back-projection
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0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Eye blink correction (remove IC)
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Eye blink correction (remove IC)
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Eye blink correction (remove IC)
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Eye blink correction (remove IC)
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Evaluating ICA components
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Extract epochs
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Extract epochs
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Reject data epochs (automatic)
>> EEG = pop_autorej(EEG, 'nogui', 'on', 'eegplot', 'on');
High enough
to keep
eye blinks
High standard
deviation,
multiples
passes
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Component ERP envelope
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Definition: The data envelope
Data (all channels)
Data envelope
(max/min traces)
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
IC back-projection envelope
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
IC back-projection envelope
IC envelopes
plotted for simplicity
(instead of all
back-projected
channels)
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
IC contributions to ERP envelope
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Artifact
Components
IC contributions to ERP envelope
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Evaluating ICA components
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Component ERP image
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Component ERP Images
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Component ERP Images
10 12 0
Phase-sorted image
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Component ERP Images
10 12
10 12 .01
0
Phase-sorted alpha power
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Component ERP Images
10 12
10 12 .01
0
'ampsort' , [0 0 10 12]
Same data: Sorted by alpha amplitude
Phase-sorted alpha power
>> help erpimage
'ampsort' = [center_ms, prcnt, freq, maxfreq] Sort epochs by amplitude.
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Component ERP Images
10 12
10 12 .01
0
'ampsort', [0 0 10 12]
Same sorting order: Amplitude vs. activations
Evaluating ICA components
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Stationary signals
0 0.5 1-1
-0.5
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0 0.5 1-1
-0.5
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0 0.5 1-1
-0.5
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Time Time
Time Time
Ma
gn
itu
de
Ma
gn
itu
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M
ag
nit
ud
e
Ma
gn
itu
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Slide courtesy of Petros Xanthopoulos, Univ. of Florida
10 Hz 2 Hz
0 0.5 1-1
-0.5
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0 0.5 1-1
-0.5
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2+10+20 Hz 20 Hz
0 0.2 0.4 0.6 0.8 1-3
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Frequency (Hz)
Power spectrum
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Figure, courtesy of Ravi Ramamoorthi & Wolberg
Freq. decomp. Sum of freq. Time
domain
Time
Frequency
Frequency
domain
Summing stationary signals and decomposing
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Average of squared absolute values
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Average of squared amplitudes
Overlap 50%
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
0 ms 10 ms 20 ms 30 ms 40 ms 50 ms 60 ms
5 Hz
10 Hz
20 Hz
30 Hz
5 Hz
10 Hz
20 Hz
30 Hz
0 ms 10 ms 20 ms 30 ms 40 ms 50 ms 60 ms
Average of
squared
values
Spectrogram or ERSP
Absolute = ERS
Relative = ERSP (dB or %)
Absolute versus relative power
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
FFT Wavelet
Fre
quency
Difference between FFT and wavelets
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Time-frequency resolution trade off
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
FFT
In between
Pure wavelet
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Wavelet (0)= FFT Wavelet (1)
1Hz
2Hz
4Hz
6Hz
8Hz
10Hz
Wavelets factor
exact same number of
wavelets at all freqs
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Wavelet (0.8) Wavelet (0.5) Wavelet (0.2)
Modified wavelets
Scaled to require more wavelets at higher freqs (less than FFT though)
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Slide courtesy of Stefan Debener Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Evaluating ICA components
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Plot IC ERSP
Time points lost at
beginning and end of epoch!
Plot IC ERSP
Pure green denotes
non-significant points
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Plot IC ERSP
Increase # freq bins
padratio = 1 padratio = 2
Evaluating ICA components
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Cortex
Two EEG channels
A
Scalp channel coherence includes source confounds!
B C
Scalp channel coherence confounds
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Is the observed
coherence from
C getting stronger?
Or B and C becoming
synchronous?
Cortex C
A B
MANY EEG channels
Separate out
independent EEG
components Measure their
synchronization
Scalp channel coherence confounds
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Cross-coherence amplitude and phase
Animal picture Distractor picture P
ha
se
(d
eg
ree
) A
mp
litu
de
(0
-1)
5 6
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
IC cross coherence
Be sure to mask by
bootstrap significance limits
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
IC cross coherence
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
coherence
phase lag
Exercise
• ALL
- Load stern.set, epoch on Memorize letters, reject noisy epochs
• Novice
- From the GUI, plot component ERPs with maps
- Plot an IC ERP image; try sorting by RT or phase, is there any
effect of the time-locking event on the activation pattern?
- Try plotting power in a specified frequency band; how consistent
are any power changes across trials?
• Intermediate
- Plot ERSPs for an IC; for FFT, vary the 'winsize' and 'padratio';
for wavelets, vary number of 'cycles' and window size factor
- Compare FFT and wavelet methods; Do the results agree?
- Plot ERSPs with no baseline and with different baseline periods;
how might this affect your results/conclusions?
• Advanced
- Plot cross coherence between two selected ICs
> Compare this result with cross coherence between two
channels that are highly weighted in the respective ICs
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
Supplementary lessons
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
2 components, comparison on the same trials
Coherence amplitude 1
Phase coherence 0
Coherence amplitude 1
Phase coherence 90
Coherence amplitude 1
Phase coherence 180
Tri
al 1
T
rial
2
Tri
al 3
COHERENCE = mean(phase vector) Norm 0.33
Phase 90 degree
Cross-coherence amplitude and phase
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
IC ERP difference
What is the IC ERP difference between these 2 conditions?
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
IC ERP difference
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
IC ERP difference
Novice EEGLAB Workshop, Sept 22, 2011, Mallorca, Spain: Julie Onton – IC Analysis Tools
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