Event-Related Spectral Perturbation (ERSP)

Computes Event-Related Spectral Perturbation for epoched (3D) EEG data. ERSP quantifies event-related changes in spectral power relative to a baseline period, expressed in decibels (dB). Uses the Morlet wavelet transform to compute time-frequency decomposition for each epoch, then averages power across epochs and normalizes to baseline.

Usage

eegERSP(
  x,
  baseline = c(1, 50),
  frequencies = NULL,
  n_cycles = 7,
  assay_name = NULL,
  output_assay = "ersp_data"
)

Arguments

x: A PhysioExperiment object with epoched (3D) EEG data (time x channels x epochs).
baseline: Numeric vector of length 2 specifying the baseline time window in sample indices (e.g., c(1, 50) for the first 50 samples). Default is c(1, 50).
frequencies: Numeric vector of frequencies in Hz to analyze. If NULL, defaults to seq(1, 50, by = 1).
n_cycles: Number of cycles for the Morlet wavelet (default: 7).
assay_name: Name of the input assay. If NULL, the default assay is used.
output_assay: Name of the assay to store ERSP results (default: "ersp").

Value

Modified PhysioExperiment with:

3D ERSP array (time x frequencies x channels) in dB in output_assay
Baseline info and frequency vector in metadata(x)$ersp, a list containing frequencies (numeric vector), baseline (numeric vector), n_cycles (integer), and n_epochs (integer)

References

Tallon-Baudry, C., et al. (1997). Oscillatory gamma-band activity during conscious perception. Trends in Cognitive Sciences, 3(4), 151-162.

Makeig, S. (1993). Auditory event-related dynamics of the EEG spectrum and effects of exposure to tones. Electroencephalography and Clinical Neurophysiology, 86(4), 283-293.

Examples

if (FALSE) { # \dontrun{
pe <- make_eeg_erp(n_epochs = 20, n_channels = 2, sr = 250)
pe_ersp <- eegERSP(pe, baseline = c(1, 50), frequencies = seq(5, 30, by = 5))
ersp_data <- SummarizedExperiment::assay(pe_ersp, "ersp")
dim(ersp_data)  # time x frequencies x channels
} # }