Phase Lag Index (PLI)

Computes the Phase Lag Index between two signals. PLI measures the asymmetry of the distribution of phase differences and is insensitive to zero-lag (volume conduction) effects.

Usage

phaseLagIndex(
  x,
  y = NULL,
  sr = NULL,
  freq_band,
  modality_x = NULL,
  modality_y = NULL,
  channels_x = 1L,
  channels_y = 1L
)

Arguments

x: Numeric vector, PhysioExperiment, or MultiPhysioExperiment.
y: Numeric vector or PhysioExperiment (NULL when x is an MPE).
sr: Numeric sampling rate in Hz (required when x/y are numeric).
freq_band: Numeric vector of length 2 specifying the frequency band c(low, high) in Hz. Required.
modality_x: Character modality name in MPE for x signal.
modality_y: Character modality name in MPE for y signal.
channels_x: Integer channel index to extract from x (default 1).
channels_y: Integer channel index to extract from y (default 1).

Value

A named list with components:

pli: Numeric scalar in [0, 1] – the Phase Lag Index.
phase_diff: Numeric vector of instantaneous phase differences (radians).

Details

$$\text{PLI} = \left|\frac{1}{N} \sum_{t=1}^{N} \text{sign}(\sin(\phi_x(t) - \phi_y(t)))\right|$$

A PLI of 0 indicates either no coupling or symmetric (zero-lag) coupling. A PLI of 1 indicates perfect non-zero-lag phase locking.

References

Stam, C. J., Nolte, G., & Daffertshofer, A. (2007). Phase lag index: Assessment of functional connectivity from multi channel EEG and MEG with diminished bias from common sources. Human Brain Mapping, 28(11), 1178–1193.

Examples

sr <- 500
t <- seq(0, 2, length.out = sr * 2)
x <- sin(2 * pi * 10 * t)
y <- sin(2 * pi * 10 * t + pi / 3)
result <- phaseLagIndex(x, y, sr = sr, freq_band = c(8, 12))
result$pli
#> [1] 0.99