Compare evoked responses for different conditions

In this example, an Epochs object for visual and auditory responses is created. Both conditions are then accessed by their respective names to create a sensor layout plot of the related evoked responses.

# Authors: Denis Engemann <denis.engemann@gmail.com>
#          Alexandre Gramfort <alexandre.gramfort@inria.fr>

# License: BSD (3-clause)


import matplotlib.pyplot as plt
import mne

from mne.viz import plot_evoked_topo
from mne.datasets import sample

print(__doc__)

data_path = sample.data_path()

Set parameters

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'
tmin = -0.2
tmax = 0.5

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

#   Set up amplitude-peak rejection values for MEG channels
reject = dict(grad=4000e-13, mag=4e-12)

# Create epochs including different events
event_id = {'audio/left': 1, 'audio/right': 2,
            'visual/left': 3, 'visual/right': 4}
epochs = mne.Epochs(raw, events, event_id, tmin, tmax,
                    picks='meg', baseline=(None, 0), reject=reject)

# Generate list of evoked objects from conditions names
evokeds = [epochs[name].average() for name in ('left', 'right')]

Out:

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.
Not setting metadata
Not setting metadata
288 matching events found
Setting baseline interval to [-0.19979521315838786, 0.0] sec
Applying baseline correction (mode: mean)
Created an SSP operator (subspace dimension = 3)
4 projection items activated
    Rejecting  epoch based on MAG : ['MEG 1711']
Removing projector <Projection | Average EEG reference, active : True, n_channels : 60>
    Rejecting  epoch based on MAG : ['MEG 1711']
Removing projector <Projection | Average EEG reference, active : True, n_channels : 60>

Show topography for two different conditions

colors = 'blue', 'red'
title = 'MNE sample data\nleft vs right (A/V combined)'

plot_evoked_topo(evokeds, color=colors, title=title, background_color='w')

plt.show()

Estimated memory usage: 8 MB

Sensitivity map of SSP projections Plot custom topographies for MEG sensors