Motor-Imagery Lateralization Index (hemispheric ERD/ERS)

Quantifies the hemispheric asymmetry of sensorimotor-rhythm activity during motor imagery, a rehabilitation-relevant index of affected- versus unaffected-hemisphere engagement. For each trial a laterality index \(LI = (R - L) / (|R| + |L|)\) is computed from a right- and a left-hemisphere channel (or ROI), bounded from -1 to 1. With method = "erd" the activation is the event-related desynchronization magnitude from eegMotorImagery() (a positive LI means the right hemisphere desynchronizes more, i.e. is more active); with method = "power" it is the raw band power (a positive LI means the right hemisphere has more power). A symmetric input gives \(LI \approx 0\).

Usage

eegLateralization(
  x,
  left_ch = "C3",
  right_ch = "C4",
  band = c(8, 13),
  method = c("erd", "power"),
  baseline_fraction = 0.25,
  conf_level = 0.95,
  reliability = list(icc = NA_real_, sem = NA_real_),
  assay_name = NULL
)

Arguments

x: A PhysioExperiment object with epoched (3D) EEG data (time x channels x trials).
left_ch: Character label(s) of the left-hemisphere channel or ROI (default: "C3").
right_ch: Character label(s) of the right-hemisphere channel or ROI (default: "C4").
band: Numeric length-2 frequency band in Hz (default: c(8, 13), the mu rhythm).
method: Activation measure: "erd" (desynchronization magnitude, via eegMotorImagery()) or "power" (raw band power).
baseline_fraction: Fraction of each trial used as the ERD baseline (default: 0.25); only used by method = "erd".
conf_level: Confidence level for the summary interval (default: 0.95).
reliability: Named list of reliability indices attached to the summary biomarker (default: icc and sem placeholders).
assay_name: Input assay name (default: the default assay).

Value

A list with per_trial (an n_trials x 1 matrix of laterality indices) and summary (a PhysioBiomarker holding the mean LI with its confidence interval, reliability, and provenance).

References

Pfurtscheller, G., & Lopes da Silva, F. H. (1999). Event-related EEG/MEG synchronization and desynchronization: basic principles. Clinical Neurophysiology, 110(11), 1842-1857.

Bai, O., et al. (2005). Asymmetric spatiotemporal patterns of event-related desynchronization preceding voluntary sequential finger movements. Clinical Neurophysiology, 116(5), 1213-1221.

Examples

if (FALSE) { # \dontrun{
pe <- make_eeg_bci(n_trials = 20, n_channels = 8, sr = 256)
li <- eegLateralization(pe, method = "power")
li$summary
} # }