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In [ ]:

%matplotlib inline

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# Compute the power spectral density of raw data

This script shows how to compute the power spectral density (PSD) of measurements on a raw dataset. It also show the effect of applying SSP to the data to reduce ECG and EOG artifacts.

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In [ ]:

# Authors: Alexandre Gramfort <alexandre.gramfort@telecom-paristech.fr>
#          Martin Luessi <mluessi@nmr.mgh.harvard.edu>
#          Eric Larson <larson.eric.d@gmail.com>

import numpy as np
import matplotlib.pyplot as plt

import mne
from mne.datasets import sample
from mne.time_frequency import psd_multitaper

print(__doc__)

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Set parameters

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In [ ]:

data_path = sample.data_path()
raw_fname = data_path + '/MEG/sample/sample_audvis_raw.fif'
proj_fname = data_path + '/MEG/sample/sample_audvis_eog-proj.fif'

tmin, tmax = 0, 60  # use the first 60s of data

# Add SSP projection vectors to reduce EOG and ECG artifacts

fmin, fmax = 2, 300  # look at frequencies between 2 and 300Hz
n_fft = 2048  # the FFT size (n_fft). Ideally a power of 2

# Let's first check out all channel types
raw.plot_psd(area_mode='range', tmax=10.0, show=False)

# Now let's focus on a smaller subset:
# Pick MEG magnetometers in the Left-temporal region
picks = mne.pick_types(raw.info, meg='mag', eeg=False, eog=False,

# Let's just look at the first few channels for demonstration purposes
picks = picks[:4]

plt.figure()
ax = plt.axes()
raw.plot_psd(tmin=tmin, tmax=tmax, fmin=fmin, fmax=fmax, n_fft=n_fft,
n_jobs=1, proj=False, ax=ax, color=(0, 0, 1),  picks=picks,
show=False)

# And now do the same with SSP applied
raw.plot_psd(tmin=tmin, tmax=tmax, fmin=fmin, fmax=fmax, n_fft=n_fft,
n_jobs=1, proj=True, ax=ax, color=(0, 1, 0), picks=picks,
show=False)

# And now do the same with SSP + notch filtering
# Pick all channels for notch since the SSP projection mixes channels together
raw.notch_filter(np.arange(60, 241, 60), n_jobs=1)
raw.plot_psd(tmin=tmin, tmax=tmax, fmin=fmin, fmax=fmax, n_fft=n_fft,
n_jobs=1, proj=True, ax=ax, color=(1, 0, 0), picks=picks,
show=False)

ax.set_title('Four left-temporal magnetometers')
plt.legend(['Without SSP', 'With SSP', 'SSP + Notch'])

# Alternatively, you may also create PSDs from Raw objects with psd_XXX
f, ax = plt.subplots()
psds, freqs = psd_multitaper(raw, low_bias=True, tmin=tmin, tmax=tmax,
fmin=fmin, fmax=fmax, proj=True, picks=picks,
n_jobs=1)
psds = 10 * np.log10(psds)
psds_mean = psds.mean(0)
psds_std = psds.std(0)

ax.plot(freqs, psds_mean, color='k')
ax.fill_between(freqs, psds_mean - psds_std, psds_mean + psds_std,
color='k', alpha=.5)
ax.set(title='Multitaper PSD', xlabel='Frequency',
ylabel='Power Spectral Density (dB)')
plt.show()

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