Skip to contents

Compute Phase Lag Index (PLI)

Source: R/ops-connectivity.R
pli.Rd

Calculates the Phase Lag Index between channel pairs, a measure of asymmetry in the phase difference distribution.

Usage

pli(x, freq_band, channels = NULL, assay_name = NULL)

Arguments

x

A PhysioExperiment object.

freq_band

Numeric vector of length 2 specifying frequency band (Hz).

channels

Integer vector of channel indices.

assay_name

Input assay name.

Value

A numeric matrix of PLI values (channel x channel) with values ranging from 0 (no asymmetry in phase distribution) to 1 (maximal asymmetry). Row and column names are set to channel names when available.

Details

PLI measures the asymmetry of the distribution of phase differences. Unlike PLV, PLI is insensitive to volume conduction effects that lead to zero-lag synchronization.

PLI = |mean(sign(Im(S_xy)))|, where S_xy is the cross-spectrum.

References

Lachaux, J.-P., et al. (1999). "Measuring phase synchrony in brain signals." Human Brain Mapping, 8(4), 194-208. doi:10.1002/(SICI)1097-0193(1999)8:4<194::AID-HBM4>3.0.CO;2-C

See also

plv() for phase locking value, wPLI() for weighted phase lag index, coherence() for frequency-domain coherence, connectivityMatrix() for a unified connectivity interface.

Examples

set.seed(123)
pe <- PhysioExperiment(
  assays = list(raw = matrix(rnorm(4000), nrow = 1000, ncol = 4)),
  colData = S4Vectors::DataFrame(label = c("Fz", "Cz", "Pz", "Oz")),
  samplingRate = 256
)

# Compute PLI in alpha band (8-12 Hz)
pli_matrix <- pli(pe, freq_band = c(8, 12))