# functions. Let's define a `Support Vector Classifier <http://scikit-learn.org/stable/modules/svm.html >`_ (or SVC).
from sklearn.svm import SVC
svc = SVC()
###########################################################################
# Masking the data
# ...................................
# To use a scikit-learn estimator on brain images, you should first mask the
# data using a :class:`nilearn.maskers.NiftiMasker` to extract only the
# voxels inside the mask of interest, and transform 4D input fMRI data to
# 2D arrays(`shape=(n_timepoints, n_voxels)`) that estimators can work on.
from nilearn.maskers import NiftiMasker
masker = NiftiMasker(mask_img=mask_filename, runs=session_label,
smoothing_fwhm=4, standardize=True,
memory="nilearn_cache", memory_level=1)
fmri_masked = masker.fit_transform(fmri_niimgs)
###########################################################################
# Cross-validation with scikit-learn
# ...................................
# To train and test the model in a meaningful way we use cross-validation with
# the function :func:`sklearn.model_selection.cross_val_score` that computes
# for you the score for the different folds of cross-validation.
from sklearn.model_selection import cross_val_score
# Here `cv=5` stipulates a 5-fold cross-validation
cv_scores = cross_val_score(svc, fmri_masked, conditions, cv=5)
print("SVC accuracy: {:.3f}".format(cv_scores.mean()))
###########################################################################
# Tuning cross-validation parameters
from nilearn.image import get_data
############################################################################
# Load Localizer contrast
n_samples = 20
localizer_dataset = datasets.fetch_localizer_calculation_task(
n_subjects=n_samples, legacy_format=False)
tested_var = np.ones((n_samples, 1))
############################################################################
# Mask data
nifti_masker = NiftiMasker(smoothing_fwhm=5,
memory='nilearn_cache',
memory_level=1) # cache options
cmap_filenames = localizer_dataset.cmaps
fmri_masked = nifti_masker.fit_transform(cmap_filenames)
############################################################################
# Anova (parametric F-scores)
from sklearn.feature_selection import f_regression
_, pvals_anova = f_regression(fmri_masked, tested_var,
center=False) # do not remove intercept
pvals_anova *= fmri_masked.shape[1]
pvals_anova[np.isnan(pvals_anova)] = 1
pvals_anova[pvals_anova > 1] = 1
neg_log_pvals_anova = -np.log10(pvals_anova)
neg_log_pvals_anova_unmasked = nifti_masker.inverse_transform(
neg_log_pvals_anova)
############################################################################
# Visualization
y = y[non_rest]
# Get the labels of the numerical conditions represented by the vector y
unique_conditions, order = np.unique(y, return_index=True)
# Sort the conditions by the order of appearance
unique_conditions = unique_conditions[np.argsort(order)]
##############################################################################
# Prepare the fMRI data
# ----------------------
from nilearn.maskers import NiftiMasker
# For decoding, standardizing is often very important
nifti_masker = NiftiMasker(mask_img=mask_filename, standardize=True,
runs=session, smoothing_fwhm=4,
memory="nilearn_cache", memory_level=1)
X = nifti_masker.fit_transform(func_filename)
# Remove the "rest" condition
X = X[non_rest]
session = session[non_rest]
##############################################################################
# Build the decoders, using scikit-learn
# ----------------------------------------
# Here we use a Support Vector Classification, with a linear kernel,
# and a simple feature selection step
from sklearn.svm import SVC
from sklearn.feature_selection import SelectKBest, f_classif
from sklearn.multiclass import OneVsOneClassifier, OneVsRestClassifier
from sklearn.pipeline import Pipeline
gm_imgs_train, gm_imgs_test, age_train, age_test = train_test_split(
gray_matter_map_filenames, age, train_size=.6, random_state=0)
# print basic information on the dataset
print('First gray-matter anatomy image (3D) is located at: %s' %
oasis_dataset.gray_matter_maps[0]) # 3D data
print('First white-matter anatomy image (3D) is located at: %s' %
oasis_dataset.white_matter_maps[0]) # 3D data
#############################################################################
# Preprocess data
# ----------------
nifti_masker = NiftiMasker(standardize=False,
smoothing_fwhm=2,
memory='nilearn_cache') # cache options
gm_maps_masked = nifti_masker.fit_transform(gm_imgs_train)
# The features with too low between-subject variance are removed using
# :class:`sklearn.feature_selection.VarianceThreshold`.
from sklearn.feature_selection import VarianceThreshold
variance_threshold = VarianceThreshold(threshold=.01)
gm_maps_thresholded = variance_threshold.fit_transform(gm_maps_masked)
# Then we convert the data back to the mask image in order to use it for
# decoding process
mask = nifti_masker.inverse_transform(variance_threshold.get_support())
############################################################################
# Prediction pipeline with ANOVA and SVR using
# :class:`nilearn.decoding.DecoderRegressor` Object
print('First subject functional nifti image (4D) is at: %s' %
dataset.func[0]) # 4D data
#####################################################################
# Preprocess
from nilearn.maskers import NiftiMasker
# This is fmri timeseries data: the background has not been removed yet,
# thus we need to use mask_strategy='epi' to compute the mask from the
# EPI images
masker = NiftiMasker(smoothing_fwhm=8,
memory='nilearn_cache',
memory_level=1,
mask_strategy='epi',
standardize=True)
data_masked = masker.fit_transform(func_filename)
#####################################################################
# Apply ICA
from sklearn.decomposition import FastICA
n_components = 10
ica = FastICA(n_components=n_components, random_state=42)
components_masked = ica.fit_transform(data_masked.T).T
# Normalize estimated components, for thresholding to make sense
components_masked -= components_masked.mean(axis=0)
components_masked /= components_masked.std(axis=0)
# Threshold
import numpy as np
components_masked[np.abs(components_masked) < .8] = 0
# The NiftiMasker report allows us to see the mask before and after resampling.
# Simply hover over the report to see the mask from the original image.
import numpy as np
masker = NiftiMasker(mask_strategy='epi', target_affine=np.eye(3) * 8)
masker.fit(epi_img)
report = masker.generate_report()
report
###############################################################################
# After mask computation: extracting time series
###############################################################################
#
# Extract time series
# trended vs detrended
trended = NiftiMasker(mask_strategy='epi')
detrended = NiftiMasker(mask_strategy='epi', detrend=True)
trended_data = trended.fit_transform(epi_img)
detrended_data = detrended.fit_transform(epi_img)
# The timeseries are numpy arrays, so we can manipulate them with numpy
print("Trended: mean %.2f, std %.2f" %
(np.mean(trended_data), np.std(trended_data)))
print("Detrended: mean %.2f, std %.2f" %
(np.mean(detrended_data), np.std(detrended_data)))
show()
verbose=1,
cv=cv)
searchlight.fit(fmri_img, y)
#########################################################################
# F-scores computation
# ----------------------
from nilearn.maskers import NiftiMasker
# For decoding, standardizing is often very important
nifti_masker = NiftiMasker(mask_img=mask_img,
runs=session,
standardize=True,
memory='nilearn_cache',
memory_level=1)
fmri_masked = nifti_masker.fit_transform(fmri_img)
from sklearn.feature_selection import f_classif
f_values, p_values = f_classif(fmri_masked, y)
p_values = -np.log10(p_values)
p_values[p_values > 10] = 10
p_unmasked = get_data(nifti_masker.inverse_transform(p_values))
#########################################################################
# Visualization
# --------------
# Use the fmri mean image as a surrogate of anatomical data
from nilearn import image
mean_fmri = image.mean_img(fmri_img)
from nilearn.plotting import plot_stat_map, plot_img, show
from nilearn.maskers import NiftiMasker
brain_masker = NiftiMasker(smoothing_fwhm=6,
detrend=True,
standardize=True,
low_pass=0.1,
high_pass=0.01,
t_r=2,
memory='nilearn_cache',
memory_level=1,
verbose=0)
##########################################################################
# Then we extract the brain-wide voxel-wise time series while regressing
# out the confounds as before
brain_time_series = brain_masker.fit_transform(func_filename,
confounds=[confound_filename])
##########################################################################
# We can now inspect the extracted time series. Note that the **seed time
# series** is an array with shape n_volumes, 1), while the
# **brain time series** is an array with shape (n_volumes, n_voxels).
print("Seed time series shape: (%s, %s)" % seed_time_series.shape)
print("Brain time series shape: (%s, %s)" % brain_time_series.shape)
##########################################################################
# We can plot the **seed time series**.
import matplotlib.pyplot as plt
plt.plot(seed_time_series)
sessions = labels['chunks']
condition_mask = conditions.isin(['face', 'house'])
conditions_encoded = conditions_encoded[condition_mask]
##############################################################################
# Mask data
mask_filename = haxby_dataset.mask
from nilearn.image import index_img
from nilearn.maskers import NiftiMasker
nifti_masker = NiftiMasker(smoothing_fwhm=8,
mask_img=mask_filename,
memory='nilearn_cache',
memory_level=1) # cache options
func_filename = haxby_dataset.func[0]
func_reduced = index_img(func_filename, condition_mask)
fmri_masked = nifti_masker.fit_transform(func_reduced)
# We consider the mean image per session and per condition.
# Otherwise, the observations cannot be exchanged at random because
# a time dependence exists between observations within a same session.
n_sessions = np.unique(sessions).size
grouped_fmri_masked = np.empty((
2 * n_sessions, # two conditions per session
fmri_masked.shape[1]))
grouped_conditions_encoded = np.empty((2 * n_sessions, 1))
for s in range(n_sessions):
session_mask = sessions[condition_mask] == s
session_house_mask = np.logical_and(session_mask,
conditions[condition_mask] == 'house')
session_face_mask = np.logical_and(session_mask,