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Compute cross-talk functions for LCMV beamformers#
Visualise cross-talk functions at one vertex for LCMV beamformers computed with different data covariance matrices, which affects their cross-talk functions.
# Author: Olaf Hauk <olaf.hauk@mrc-cbu.cam.ac.uk>
#
# License: BSD-3-Clause
import mne
from mne.datasets import sample
from mne.beamformer import make_lcmv, make_lcmv_resolution_matrix
from mne.minimum_norm import get_cross_talk
print(__doc__)
data_path = sample.data_path()
subjects_dir = data_path / 'subjects'
meg_path = data_path / 'MEG' / 'sample'
fname_fwd = meg_path / 'sample_audvis-meg-eeg-oct-6-fwd.fif'
fname_cov = meg_path / 'sample_audvis-cov.fif'
fname_evo = meg_path / 'sample_audvis-ave.fif'
raw_fname = meg_path / 'sample_audvis_filt-0-40_raw.fif'
# Read raw data
raw = mne.io.read_raw_fif(raw_fname)
# only pick good EEG/MEG sensors
raw.info['bads'] += ['EEG 053'] # bads + 1 more
picks = mne.pick_types(raw.info, meg=True, eeg=True, exclude='bads')
# Find events
events = mne.find_events(raw)
# event_id = {'aud/l': 1, 'aud/r': 2, 'vis/l': 3, 'vis/r': 4}
event_id = {'vis/l': 3, 'vis/r': 4}
tmin, tmax = -.2, .25 # epoch duration
epochs = mne.Epochs(raw, events, event_id=event_id, tmin=tmin, tmax=tmax,
picks=picks, baseline=(-.2, 0.), preload=True)
del raw
# covariance matrix for pre-stimulus interval
tmin, tmax = -.2, 0.
cov_pre = mne.compute_covariance(epochs, tmin=tmin, tmax=tmax,
method='empirical')
# covariance matrix for post-stimulus interval (around main evoked responses)
tmin, tmax = 0.05, .25
cov_post = mne.compute_covariance(epochs, tmin=tmin, tmax=tmax,
method='empirical')
info = epochs.info
del epochs
# read forward solution
forward = mne.read_forward_solution(fname_fwd)
# use forward operator with fixed source orientations
mne.convert_forward_solution(forward, surf_ori=True,
force_fixed=True, copy=False)
# read noise covariance matrix
noise_cov = mne.read_cov(fname_cov)
# regularize noise covariance (we used 'empirical' above)
noise_cov = mne.cov.regularize(noise_cov, info, mag=0.1, grad=0.1,
eeg=0.1, rank='info')
Opening raw data file /home/circleci/mne_data/MNE-sample-data/MEG/sample/sample_audvis_filt-0-40_raw.fif...
Read a total of 4 projection items:
PCA-v1 (1 x 102) idle
PCA-v2 (1 x 102) idle
PCA-v3 (1 x 102) idle
Average EEG reference (1 x 60) idle
Range : 6450 ... 48149 = 42.956 ... 320.665 secs
Ready.
319 events found
Event IDs: [ 1 2 3 4 5 32]
Not setting metadata
143 matching events found
Applying baseline correction (mode: mean)
Created an SSP operator (subspace dimension = 4)
4 projection items activated
Loading data for 143 events and 69 original time points ...
0 bad epochs dropped
Computing rank from data with rank=None
Using tolerance 4.9e-09 (2.2e-16 eps * 305 dim * 7.3e+04 max singular value)
Estimated rank (mag + grad): 302
MEG: rank 302 computed from 305 data channels with 3 projectors
Using tolerance 2.8e-11 (2.2e-16 eps * 59 dim * 2.1e+03 max singular value)
Estimated rank (eeg): 58
EEG: rank 58 computed from 59 data channels with 1 projector
Created an SSP operator (subspace dimension = 4)
Setting small MEG eigenvalues to zero (without PCA)
Setting small EEG eigenvalues to zero (without PCA)
Reducing data rank from 364 -> 360
Estimating covariance using EMPIRICAL
Done.
Number of samples used : 4433
[done]
Computing rank from data with rank=None
Using tolerance 5.9e-09 (2.2e-16 eps * 305 dim * 8.7e+04 max singular value)
Estimated rank (mag + grad): 302
MEG: rank 302 computed from 305 data channels with 3 projectors
Using tolerance 3.8e-11 (2.2e-16 eps * 59 dim * 2.9e+03 max singular value)
Estimated rank (eeg): 58
EEG: rank 58 computed from 59 data channels with 1 projector
Created an SSP operator (subspace dimension = 4)
Setting small MEG eigenvalues to zero (without PCA)
Setting small EEG eigenvalues to zero (without PCA)
Reducing data rank from 364 -> 360
Estimating covariance using EMPIRICAL
Done.
Number of samples used : 4433
[done]
Reading forward solution from /home/circleci/mne_data/MNE-sample-data/MEG/sample/sample_audvis-meg-eeg-oct-6-fwd.fif...
Reading a source space...
Computing patch statistics...
Patch information added...
Distance information added...
[done]
Reading a source space...
Computing patch statistics...
Patch information added...
Distance information added...
[done]
2 source spaces read
Desired named matrix (kind = 3523) not available
Read MEG forward solution (7498 sources, 306 channels, free orientations)
Desired named matrix (kind = 3523) not available
Read EEG forward solution (7498 sources, 60 channels, free orientations)
Forward solutions combined: MEG, EEG
Source spaces transformed to the forward solution coordinate frame
Average patch normals will be employed in the rotation to the local surface coordinates....
Converting to surface-based source orientations...
[done]
366 x 366 full covariance (kind = 1) found.
Read a total of 4 projection items:
PCA-v1 (1 x 102) active
PCA-v2 (1 x 102) active
PCA-v3 (1 x 102) active
Average EEG reference (1 x 60) active
Computing rank from covariance with rank='info'
MEG: rank 302 after 3 projectors applied to 305 channels
EEG: rank 58 after 1 projector applied to 59 channels
8 projection items activated
MAG regularization : 0.1
Created an SSP operator (subspace dimension = 3)
Computing rank from covariance with rank={'meg': 302, 'eeg': 58}
Using tolerance 2.5e-14 (2.2e-16 eps * 102 dim * 1.1 max singular value)
Estimated rank (mag): 99
MAG: rank 99 computed from 102 data channels with 3 projectors
Setting small MAG eigenvalues to zero (without PCA)
GRAD regularization : 0.1
Computing rank from covariance with rank={'meg': 302, 'eeg': 58, 'mag': 99}
Using tolerance 1.8e-13 (2.2e-16 eps * 203 dim * 3.9 max singular value)
Estimated rank (grad): 203
GRAD: rank 203 computed from 203 data channels with 0 projectors
Setting small GRAD eigenvalues to zero (without PCA)
EEG regularization : 0.1
Created an SSP operator (subspace dimension = 1)
Computing rank from covariance with rank={'meg': 302, 'eeg': 58, 'mag': 99, 'grad': 203}
Setting small EEG eigenvalues to zero (without PCA)
Compute LCMV filters with different data covariance matrices#
# compute LCMV beamformer filters for pre-stimulus interval
filters_pre = make_lcmv(info, forward, cov_pre, reg=0.05,
noise_cov=noise_cov,
pick_ori=None, rank=None,
weight_norm=None,
reduce_rank=False,
verbose=False)
# compute LCMV beamformer filters for post-stimulus interval
filters_post = make_lcmv(info, forward, cov_post, reg=0.05,
noise_cov=noise_cov,
pick_ori=None, rank=None,
weight_norm=None,
reduce_rank=False,
verbose=False)
Compute resolution matrices for the two LCMV beamformers#
# compute cross-talk functions (CTFs) for one target vertex
sources = [3000]
verttrue = [forward['src'][0]['vertno'][sources[0]]] # pick one vertex
rm_pre = make_lcmv_resolution_matrix(filters_pre, forward, info)
stc_pre = get_cross_talk(rm_pre, forward['src'], sources, norm=True)
del rm_pre
364 out of 366 channels remain after picking
Dimensions of LCMV resolution matrix: 7498 by 7498.
rm_post = make_lcmv_resolution_matrix(filters_post, forward, info)
stc_post = get_cross_talk(rm_post, forward['src'], sources, norm=True)
del rm_post
364 out of 366 channels remain after picking
Dimensions of LCMV resolution matrix: 7498 by 7498.
Visualize#
Pre:
brain_pre = stc_pre.plot('sample', 'inflated', 'lh', subjects_dir=subjects_dir,
figure=1, clim=dict(kind='value', lims=(0, .2, .4)))
brain_pre.add_text(0.1, 0.9, 'LCMV beamformer with pre-stimulus\ndata '
'covariance matrix', 'title', font_size=16)
# mark true source location for CTFs
brain_pre.add_foci(verttrue, coords_as_verts=True, scale_factor=1., hemi='lh',
color='green')
Post:
brain_post = stc_post.plot('sample', 'inflated', 'lh',
subjects_dir=subjects_dir,
figure=2, clim=dict(kind='value', lims=(0, .2, .4)))
brain_post.add_text(0.1, 0.9, 'LCMV beamformer with post-stimulus\ndata '
'covariance matrix', 'title', font_size=16)
brain_post.add_foci(verttrue, coords_as_verts=True, scale_factor=1.,
hemi='lh', color='green')
The pre-stimulus beamformer’s CTF has lower values in parietal regions suppressed alpha activity?) but larger values in occipital regions (less suppression of visual activity?).
Total running time of the script: ( 0 minutes 14.229 seconds)
Estimated memory usage: 438 MB