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Inter-Trial Coherence (ITC)

Source: R/eeg-timefreq.R
eegITC.Rd

Computes Inter-Trial Coherence (also known as phase-locking factor or phase-locking value) for epoched (3D) EEG data. ITC measures the consistency of oscillatory phase across trials at each time-frequency point. Values range from 0 (completely random phase) to 1 (perfectly phase-locked across all trials).

Usage

eegITC(
  x,
  frequencies = NULL,
  n_cycles = 7,
  assay_name = NULL,
  output_assay = "itc_data"
)

Arguments

x

A PhysioExperiment object with epoched (3D) EEG data (time x channels x epochs).

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 the result is stored under. Despite the argument's name this is a key in metadata, NOT an assay: after the call assay(x, "the value given") does not exist while metadata(x)$the value given holds the result (default: "the value given"). (default: "itc").

Value

Modified PhysioExperiment with:

  • 3D ITC array (time x frequencies x channels) in output_assay, values in [0, 1]

  • Frequency vector and parameters in metadata(x)$itc, a list containing frequencies (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.

See also

eegERSP(), eegMorletWavelet(), eegPlotSpectrogram()

Examples

pe <- make_eeg_erp(n_epochs = 20, n_channels = 2, sr = 250)
pe_itc <- eegITC(pe, frequencies = seq(5, 30, by = 5))
# results are stored in metadata(x)$itc
str(S4Vectors::metadata(pe_itc)$itc, max.level = 1)
#> List of 3
#>  $ frequencies: num [1:6] 5 10 15 20 25 30
#>  $ n_cycles   : num 7
#>  $ n_epochs   : int 20