mne.beamformer.tf_dics(epochs, forward, noise_csds, tmin, tmax, tstep, win_lengths, subtract_evoked=False, mode='fourier', freq_bins=None, frequencies=None, n_ffts=None, mt_bandwidths=None, mt_adaptive=False, mt_low_bias=True, cwt_n_cycles=7, decim=1, reg=0.05, label=None, pick_ori=None, inversion='single', weight_norm=None, normalize_fwd=True, real_filter=False, reduce_rank=False, verbose=None)[source]

5D time-frequency beamforming based on DICS.

Calculate source power in time-frequency windows using a spatial filter based on the Dynamic Imaging of Coherent Sources (DICS) beamforming approach [1]. For each time window and frequency bin combination, cross-spectral density (CSD) is computed and used to create a DICS beamformer spatial filter.

epochs : Epochs

Single trial epochs.

forward : dict

Forward operator.

noise_csds : list of instances of CrossSpectralDensity | None

Noise cross-spectral density for each frequency bin. If these are specified, the DICS filters will be applied to both the signal and noise CSDs. The source power estimates for each frequency bin will be scaled by the estimated noise power (signal / noise). Specifying None will disable performing noise normalization.

tmin : float

Minimum time instant to consider.

tmax : float

Maximum time instant to consider.

tstep : float

Spacing between consecutive time windows, should be smaller than or equal to the shortest time window length.

win_lengths : list of float

Time window lengths in seconds. One time window length should be provided for each frequency bin.

subtract_evoked : bool

If True, subtract the averaged evoked response prior to computing the tf source grid. Defaults to False.

mode : ‘fourier’ | ‘multitaper’ | ‘cwt_morlet’

Spectrum estimation mode. Defaults to ‘fourier’.

freq_bins : list of tuples of float

Start and end point of frequency bins of interest. Only used in ‘multitaper’ or ‘fourier’ mode. For ‘cwt_morlet’ mode, use the frequencies parameter instead.

frequencies : list of float | list of lists of float

The frequencies to compute the source power for. If you want to compute the average power for multiple frequency bins, specify a list of lists: each list containing the frequencies for the corresponding bin. Only used in ‘cwt_morlet’ mode. In other modes, use the freq_bins parameter instead.

n_ffts : list | None

Length of the FFT for each frequency bin. If None (the default), the exact number of samples between tmin and tmax will be used. Only used in ‘multitaper’ or ‘fourier’ mode.

mt_bandwidths : list of float

The bandwidths of the multitaper windowing function in Hz. Only used in ‘multitaper’ mode. One value should be provided for each frequency bin. Defaults to None.

mt_adaptive : bool

Use adaptive weights to combine the tapered spectra into CSD. Only used in ‘multitaper’ mode. Defaults to False.

mt_low_bias : bool

Only use tapers with more than 90% spectral concentration within bandwidth. Only used in ‘multitaper’ mode. Defaults to True.

cwt_n_cycles: float | list of float | None

Number of cycles to use when constructing Morlet wavelets. Fixed number or one per frequency. Defaults to 7. Only used in ‘cwt_morlet’ mode.

decim : int | slice

To reduce memory usage, decimation factor during time-frequency decomposition. Defaults to 1 (no decimation). Only used in ‘cwt_morlet’ mode.

If int, uses tfr[…, ::decim]. If slice, uses tfr[…, decim].

reg : float

Regularization to use for the DICS beamformer computation. Defaults to 0.05.

label : Label | None

Restricts the solution to a given label. Defaults to None.

pick_ori : None | ‘normal’ | ‘max-power’

The source orientation to estimate source power for:

None :

orientations are pooled. (Default)

‘normal’ :

filters are computed for the orientation tangential to the cortical surface

‘max-power’ :

filters are computer for the orientation that maximizes spectral power.

Defaults to None.

inversion : ‘single’ | ‘matrix’

This determines how the beamformer deals with source spaces in “free” orientation. Such source spaces define three orthogonal dipoles at each source point. When inversion='single', each dipole is considered as an individual source and the corresponding spatial filter is computed for each dipole separately. When inversion='matrix', all three dipoles at a source vertex are considered as a group and the spatial filters are computed jointly using a matrix inversion. While inversion='single' is more stable, inversion='matrix' is more precise. See section 5 of [4]_. Defaults to ‘single’.

weight_norm : None | ‘unit-noise-gain’

How to normalize the beamformer weights. None means no normalization is performed. If ‘unit-noise-gain’, the unit-noise gain minimum variance beamformer will be computed (Borgiotti-Kaplan beamformer) [2]. Defaults to None.

normalize_fwd : bool

Whether to normalize the forward solution. Defaults to True. Note that this normalization is not required when weight normalization (weight_norm) is used.

real_filter : bool

If True, take only the real part of the cross-spectral-density matrices to compute real filters. Defaults to False.

reduce_rank : bool

If True, the rank of the forward operator will be reduced by 1 for each spatial location, prior to inversion. This may be necessary when you use a single sphere model for MEG and mode='vertex'. Defaults to False.

verbose : bool, str, int, None

If not None, override default verbose level (see mne.verbose() and Logging documentation for more).

stcs : list of SourceEstimate | VolSourceEstimate

Source power at each time window. One SourceEstimate object is returned for each frequency bin.


Dalal et al. [1] used a synthetic aperture magnetometry beamformer (SAM) in each time-frequency window instead of DICS.

An alternative to using noise CSDs is to normalize the forward solution (normalize_fwd) or the beamformer weights (weight_norm). In this case, noise_csds may be set to None.


[1](1, 2, 3) Dalal et al. Five-dimensional neuroimaging: Localization of the time-frequency dynamics of cortical activity. NeuroImage (2008) vol. 40 (4) pp. 1686-1700
[2](1, 2) Sekihara & Nagarajan. Adaptive spatial filters for electromagnetic brain imaging (2008) Springer Science & Business Media

Examples using mne.beamformer.tf_dics