Module: modalities.fmri.glm

Inheritance diagram for nipy.modalities.fmri.glm:

Inheritance diagram of nipy.modalities.fmri.glm

This module presents an interface to use the glm implemented in nipy.algorithms.statistics.models.regression.

It contains the GLM and contrast classes that are meant to be the main objects of fMRI data analyses.

It is important to note that the GLM is meant as a one-session General Linear Model. But inference can be performed on multiple sessions by computing fixed effects on contrasts


>>> import numpy as np
>>> from nipy.modalities.fmri.glm import GeneralLinearModel
>>> n, p, q = 100, 80, 10
>>> X, Y = np.random.randn(p, q), np.random.randn(p, n)
>>> cval = np.hstack((1, np.zeros(9)))
>>> model = GeneralLinearModel(X)
>>> z_vals = model.contrast(cval).z_score() # z-transformed statistics

Example of fixed effects statistics across two contrasts

>>> cval_ = cval.copy()
>>> np.random.shuffle(cval_)
>>> z_ffx = (model.contrast(cval) + model.contrast(cval_)).z_score()



class nipy.modalities.fmri.glm.Contrast(effect, variance, dof=10000000000.0, contrast_type='t', tiny=1e-50, dofmax=10000000000.0)

Bases: object

The contrast class handles the estimation of statistical contrasts on a given model: student (t), Fisher (F), conjunction (tmin-conjunction). The important feature is that it supports addition, thus opening the possibility of fixed-effects models.

The current implementation is meant to be simple, and could be enhanced in the future on the computational side (high-dimensional F contrasts may lead to memory breakage).


The ‘tmin-conjunction’ test is the valid conjunction test discussed in: Nichols T, Brett M, Andersson J, Wager T, Poline JB. Valid conjunction inference with the minimum statistic. Neuroimage. 2005 Apr 15;25(3):653-60. This test gives the p-value of the z-values under the conjunction null, i.e. the union of the null hypotheses for all terms.

__init__(effect, variance, dof=10000000000.0, contrast_type='t', tiny=1e-50, dofmax=10000000000.0)
effect: array of shape (contrast_dim, n_voxels)

the effects related to the contrast

variance: array of shape (contrast_dim, contrast_dim, n_voxels)

the associated variance estimate

dof: scalar, the degrees of freedom
contrast_type: string to be chosen among ‘t’ and ‘F’

Return a parametric estimate of the p-value associated with the null hypothesis: (H0) ‘contrast equals baseline’

baseline: float, optional

Baseline value for the test statistic


The value of 0.5 is used where the stat is not defined


Return the decision statistic associated with the test of the null hypothesis: (H0) ‘contrast equals baseline’

baseline: float, optional,

Baseline value for the test statistic


Return a parametric estimation of the z-score associated with the null hypothesis: (H0) ‘contrast equals baseline’

baseline: float, optional

Baseline value for the test statistic


The value of 0 is used where the stat is not defined


class nipy.modalities.fmri.glm.FMRILinearModel(fmri_data, design_matrices, mask='compute', m=0.2, M=0.9, threshold=0.5)

Bases: object

This class is meant to handle GLMs from a higher-level perspective i.e. by taking images as input and output

__init__(fmri_data, design_matrices, mask='compute', m=0.2, M=0.9, threshold=0.5)

Load the data

fmri_dataImage or str or sequence of Images / str

fmri images / paths of the (4D) fmri images

design_matricesarrays or str or sequence of arrays / str

design matrix arrays / paths of .npz files

maskstr or Image or None, optional

string can be ‘compute’ or a path to an image image is an input (assumed binary) mask image(s), if ‘compute’, the mask is computed if None, no masking will be applied

m, M, threshold: float, optional

parameters of the masking procedure. Should be within [0, 1]


The only computation done here is mask computation (if required)


We need the example data package for this example:

from nipy.utils import example_data
from nipy.modalities.fmri.glm import FMRILinearModel
fmri_files = [example_data.get_filename('fiac', 'fiac0', run)
    for run in ['run1.nii.gz', 'run2.nii.gz']]
design_files = [example_data.get_filename('fiac', 'fiac0', run)
    for run in ['run1_design.npz', 'run2_design.npz']]
mask = example_data.get_filename('fiac', 'fiac0', 'mask.nii.gz')
multi_session_model = FMRILinearModel(fmri_files,
z_image, = multi_session_model.contrast([np.eye(13)[1]] * 2)

# The number of voxels with p < 0.001 given by ...
print(np.sum(z_image.get_fdata() > 3.09))
contrast(contrasts, con_id='', contrast_type=None, output_z=True, output_stat=False, output_effects=False, output_variance=False)

Estimation of a contrast as fixed effects on all sessions

contrastsarray or list of arrays of shape (n_col) or (n_dim, n_col)

where n_col is the number of columns of the design matrix, numerical definition of the contrast (one array per run)

con_idstr, optional

name of the contrast

contrast_type{‘t’, ‘F’, ‘tmin-conjunction’}, optional

type of the contrast

output_zbool, optional

Return or not the corresponding z-stat image

output_statbool, optional

Return or not the base (t/F) stat image

output_effectsbool, optional

Return or not the corresponding effect image

output_variancebool, optional

Return or not the corresponding variance image

output_imageslist of nibabel images

The required output images, in the following order: z image, stat(t/F) image, effects image, variance image

fit(do_scaling=True, model='ar1', steps=100)

Load the data, mask the data, scale the data, fit the GLM

do_scalingbool, optional

if True, the data should be scaled as percent of voxel mean

modelstring, optional,

the kind of glm (‘ols’ or ‘ar1’) you want to fit to the data

stepsint, optional

in case of an ar1, discretization of the ar1 parameter


class nipy.modalities.fmri.glm.GeneralLinearModel(X)

Bases: object

This class handles the so-called on General Linear Model

Most of what it does in the fit() and contrast() methods fit() performs the standard two-step (‘ols’ then ‘ar1’) GLM fitting contrast() returns a contrast instance, yileding statistics and p-values. The link between fit() and contrast is done vis the two class members:

glm_resultsdictionary of nipy.algorithms.statistics.models.

regression.RegressionResults instances, describing results of a GLM fit

labelsarray of shape(n_voxels),

labels that associate each voxel with a results key

Xarray of shape (n_time_points, n_regressors)

the design matrix

contrast(con_val, contrast_type=None)

Specify and estimate a linear contrast

con_valnumpy.ndarray of shape (p) or (q, p)

where q = number of contrast vectors and p = number of regressors

contrast_type{None, ‘t’, ‘F’ or ‘tmin-conjunction’}, optional

type of the contrast. If None, then defaults to ‘t’ for 1D con_val and ‘F’ for 2D con_val

con: Contrast instance
fit(Y, model='ols', steps=100)

GLM fitting of a dataset using ‘ols’ regression or the two-pass

Yarray of shape(n_time_points, n_samples)

the fMRI data

model{‘ar1’, ‘ols’}, optional

the temporal variance model. Defaults to ‘ols’

stepsint, optional

Maximum number of discrete steps for the AR(1) coef histogram


Accessor for the best linear unbiased estimated of model parameters

column_index: int or array-like of int or None, optional

The indexed of the columns to be returned. if None (default behaviour), the whole vector is returned

beta: array of shape (n_voxels, n_columns)

the beta


Accessor for the log-likelihood of the model

logL: array of shape (n_voxels,)

the sum of square error per voxel


Accessor for the mean squared error of the model

mse: array of shape (n_voxels)

the sum of square error per voxel



Scaling of the data to have percent of baseline change columnwise

Y: array of shape(n_time_points, n_voxels)

the input data

Y: array of shape (n_time_points, n_voxels),

the data after mean-scaling, de-meaning and multiplication by 100

meanarray of shape (n_voxels,)

the data mean