Phase Slope Index (directed, volume-conduction robust)

The Phase Slope Index (Nolte et al. 2008) estimates the direction of information flow from the slope of the coherency phase across a frequency band, and is insensitive to instantaneous (zero-lag) mixing. Positive values indicate that x leads (drives) y.

Usage

phaseSlopeIndex(
  x,
  y = NULL,
  sr = NULL,
  freq_band,
  nperseg = 256L,
  noverlap = NULL,
  normalize = TRUE,
  modality_x = NULL,
  modality_y = NULL,
  channels_x = 1L,
  channels_y = 1L
)

Arguments

x, y

Signals (or a single object from which a pair is extracted).

sr

Sampling rate in Hz.

freq_band

Numeric c(low, high) band in Hz.

nperseg, noverlap

Welch segment length / overlap for the cross-spectrum.

normalize

If TRUE (default), scale into [-1, 1] by the summed coherency magnitude; if FALSE, return the raw imaginary sum.

modality_x, modality_y, channels_x, channels_y

Passed to the internal signal-pair extractor.

Value

A single Phase Slope Index value.

References

Nolte G, et al. (2008). Robustly estimating the flow direction of information in complex physical systems. Phys Rev Lett 100:234101. doi:10.1103/PhysRevLett.100.234101

Examples

set.seed(1); sr <- 200; n <- 4000
x <- as.numeric(stats::filter(rnorm(n), rep(1/5, 5), sides = 2)); x[is.na(x)] <- 0
y <- c(rep(0, 8), x[seq_len(n - 8)])          # y lags x
phaseSlopeIndex(x, y, sr = sr, freq_band = c(1, 40))
#> [1] 0.1940465