Directed Transfer Function (DTF)

Estimates frequency-resolved directed connectivity between EEG channels with the Directed Transfer Function (Kaminski & Blinowska 1991), computed from the transfer function \(H(f)\) of a multivariate autoregressive (MVAR) model fitted with PhysioCore::mvarFit(). Because \(H(f)\) inverts the whole VAR system, DTF reflects both direct and indirect pathways. The (default) normalized DTF satisfies \(\sum_j \mathrm{DTF}_{ij}(f)^2 = 1\) for each target \(i\) (inflow normalization); ffDTF normalizes across all frequencies instead (Korzeniewska 2003).

Usage

eegDTF(
  x,
  order = NULL,
  freqs = NULL,
  normalized = TRUE,
  ffDTF = FALSE,
  band = NULL,
  method = "ols",
  assay_name = NULL
)

Arguments

x

A PhysioExperiment object with 2D EEG data (time x channels).

order

MVAR model order, or NULL to select automatically.

freqs

Numeric vector of frequencies in Hz (default: 128 points from 0 to the Nyquist frequency).

normalized

Row-normalize the DTF (default: TRUE).

ffDTF

Use the full-frequency DTF normalization (default: FALSE).

band

Optional numeric length-2 band in Hz over which to average the stored connectivity matrix (default: all frequencies).

method

MVAR estimator passed to PhysioCore::mvarFit() (default: "ols").

assay_name

Input assay name (default: the default assay).

Value

The PhysioExperiment with metadata(x)$connectivity set to a list containing the band-averaged directed matrix (rows = targets, columns = sources), the frequency-resolved array (n_channels x n_channels x n_freqs), the frequencies, and the settings used.

References

Kaminski, M. J., & Blinowska, K. J. (1991). A new method of the description of the information flow in the brain structures. Biological Cybernetics, 65(3), 203-210.

See also

eegPDC(), eegConditionalGC(), eegConnectivityMatrix(), PhysioCore::mvarFit()

Examples

if (FALSE) { # \dontrun{
pe <- make_eeg(n_time = 4000, n_channels = 5, sr = 250)
pe <- eegDTF(pe, order = 5)
dim(metadata(pe)$connectivity$array)
} # }