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%matplotlib inline

Visualize channel over epochs as an image

This will produce what is sometimes called an event related potential / field (ERP/ERF) image.

Two images are produced, one with a good channel and one with a channel that does not show any evoked field.

It is also demonstrated how to reorder the epochs using a 1D spectral embedding as described in [1]_.



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# Authors: Alexandre Gramfort <alexandre.gramfort@telecom-paristech.fr>
#
# License: BSD (3-clause)

import numpy as np
import matplotlib.pyplot as plt

import mne
from mne import io
from mne.datasets import sample

print(__doc__)

data_path = sample.data_path()

Set parameters



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raw_fname = data_path + '/MEG/sample/sample_audvis_filt-0-40_raw.fif'
event_fname = data_path + '/MEG/sample/sample_audvis_filt-0-40_raw-eve.fif'
event_id, tmin, tmax = 1, -0.2, 0.4

# Setup for reading the raw data
raw = io.read_raw_fif(raw_fname)
events = mne.read_events(event_fname)

# Set up pick list: EEG + MEG - bad channels (modify to your needs)
raw.info['bads'] = ['MEG 2443', 'EEG 053']

# Create epochs, here for gradiometers + EOG only for simplicity
epochs = mne.Epochs(raw, events, event_id, tmin, tmax, proj=True,
                    picks=('grad', 'eog'), baseline=(None, 0), preload=True,
                    reject=dict(grad=4000e-13, eog=150e-6))

Show event-related fields images



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# and order with spectral reordering
# If you don't have scikit-learn installed set order_func to None
from sklearn.cluster.spectral import spectral_embedding  # noqa
from sklearn.metrics.pairwise import rbf_kernel   # noqa


def order_func(times, data):
    this_data = data[:, (times > 0.0) & (times < 0.350)]
    this_data /= np.sqrt(np.sum(this_data ** 2, axis=1))[:, np.newaxis]
    return np.argsort(spectral_embedding(rbf_kernel(this_data, gamma=1.),
                      n_components=1, random_state=0).ravel())


good_pick = 97  # channel with a clear evoked response
bad_pick = 98  # channel with no evoked response

# We'll also plot a sample time onset for each trial
plt_times = np.linspace(0, .2, len(epochs))

plt.close('all')
mne.viz.plot_epochs_image(epochs, [good_pick, bad_pick], sigma=.5,
                          order=order_func, vmin=-250, vmax=250,
                          overlay_times=plt_times, show=True)

References

.. [1] Graph-based variability estimation in single-trial event-related neural responses. A. Gramfort, R. Keriven, M. Clerc, 2010, Biomedical Engineering, IEEE Trans. on, vol. 57 (5), 1051-1061 https://ieeexplore.ieee.org/document/5406156