Glossary

Aliasing

Frequencies above half the sampling rate fold back into the sampled band and masquerade as lower frequencies.

First used in L1.1 · Sampling, Nyquist and aliasing

Aperiodic component

Also: 1/f background, aperiodic exponent

The broadband, power-law-like background of a spectrum, described by an offset and an exponent, separate from any peaks.

First used in L1.7 · Aperiodic and periodic components

Artifact subspace reconstruction

Also: ASR

Sliding-window PCA method that rejects or reconstructs components whose variance exceeds a calibration-data threshold.

First used in L2.7 · ASR, SSP and alternatives

Average reference

Also: common average reference

Re-referencing each channel to the mean of all channels; reduces data rank by one.

First used in L2.3 · Re-referencing

Baseline correction

Also: baseline

Subtracting the mean of a pre-stimulus window from each epoch, or modelling it as a covariate.

First used in L3.1 · Epoching and baseline

Beamformer

Also: LCMV

Spatial filter that passes activity from one source location while suppressing everything else, given the data covariance.

First used in L5.5 · The inverse problem and source estimation

BIDS

Also: EEG-BIDS, Brain Imaging Data Structure

A standard folder, file-naming and sidecar layout for neuroimaging datasets, with an EEG extension.

First used in L0.6 · Data hygiene and metadata

Burst

Also: burstiness

A transient, high-amplitude episode of an oscillation, as opposed to a sustained rhythm.

First used in L4.6 · Is it really an oscillation?

Cluster-based permutation test

Also: cluster permutation, cluster test

Nonparametric test that controls family-wise error by comparing cluster-level statistics against a permutation distribution.

First used in L3.7 · Statistics for ERPs

Coherence

Also: magnitude-squared coherence

Frequency-resolved consistency of phase and amplitude relationship between two signals, from 0 to 1.

First used in L5.1 · Volume conduction: the central problem

Common spatial patterns

Also: CSP

Spatial filters that maximize variance for one class while minimizing it for another.

First used in L5.7 · Spatial filters for decoding

Current source density

Also: CSD, surface Laplacian

Second spatial derivative of the scalp potential; reference-free and spatially sharpened.

First used in L5.3 · Surface Laplacian and CSD

Decibel

Also: dB

Logarithmic ratio unit: 10·log10 of a power ratio, or 20·log10 of an amplitude ratio.

First used in L1.2 · Time and frequency domains

Dipole

Also: equivalent current dipole

A point source–sink pair used to model the net current of a synchronously active cortical patch.

First used in L0.1 · What EEG measures

DPSS taper

Also: Slepian taper, discrete prolate spheroidal sequence

Orthogonal windows with maximal spectral concentration inside a chosen bandwidth, used in multitaper estimation.

First used in L4.3 · Multitaper and filter-Hilbert

ERD

Also: event-related desynchronization

Event-related decrease in band power relative to a baseline.

First used in L4.4 · Baseline normalization and ERD/ERS

ERP

Also: event-related potential

The average of time-locked EEG epochs, revealing activity phase-locked to an event.

First used in L3.2 · The ERP and its components

ERP image

Single trials stacked as rows of a colour image, often sorted by a variable such as reaction time.

First used in L3.6 · Single-trial approaches

ERS

Also: event-related synchronization

Event-related increase in band power relative to a baseline.

First used in L4.4 · Baseline normalization and ERD/ERS

Evoked vs induced

Also: evoked power, induced power, total power

Evoked activity is phase-locked to an event and survives averaging; induced activity is not and only appears in time-frequency power.

First used in L4.1 · Why time-frequency

FIR

Also: finite impulse response, FIR / IIR

Filter whose output is a finite weighted sum of past inputs; always stable and can be exactly linear-phase.

First used in L1.5 · Filters: FIR, IIR, and what they do to your data

Forward model

Also: head model

The physics mapping from source currents to sensor measurements for a given head geometry and conductivity.

First used in L0.1 · What EEG measures

Frequency resolution

The spacing between independent spectral estimates, equal to 1 divided by the analysis window length.

First used in L1.2 · Time and frequency domains

Group delay

The delay a filter imposes on the envelope of a signal at each frequency; constant for linear-phase filters.

First used in L1.5 · Filters: FIR, IIR, and what they do to your data

Hilbert transform

Also: analytic signal

Transform producing the analytic signal, from which instantaneous amplitude and phase of a narrowband signal follow.

First used in L4.3 · Multitaper and filter-Hilbert

ICA

Also: independent component analysis

Blind source separation that unmixes channels into statistically independent components.

First used in L2.6 · EOG regression and ICA

IIR

Also: infinite impulse response, Butterworth, FIR / IIR

Recursive filter using past outputs; short but with nonlinear phase and possible instability.

First used in L1.5 · Filters: FIR, IIR, and what they do to your data

Imaginary coherence

The imaginary part of coherency; insensitive to zero-lag mixing from volume conduction.

First used in L5.2 · Sensor-space connectivity

Impedance

Opposition to current flow at the electrode–skin interface; lower values reduce noise pickup.

First used in L0.2 · Electrodes, montages and the 10-20 system

Individual alpha frequency

Also: IAF

The frequency of a person's own alpha peak, used to individualize band definitions.

First used in L1.7 · Aperiodic and periodic components

Interpolation (spherical spline)

Also: interpolation, spherical spline

Estimating a bad channel's signal from its neighbours using spherical-spline weights.

First used in L2.2 · Channel locations and bad channels

ITC

Also: intertrial coherence, intertrial phase coherence, phase-locking factor

Consistency of phase across trials at a time-frequency point, from 0 (random) to 1 (identical).

First used in L4.5 · Phase, ITC and cross-frequency coupling

Jackknife

Leave-one-out resampling used, for example, to measure latencies on subsampled grand averages.

First used in L3.3 · Measuring ERPs

Leadfield

Also: gain matrix

The matrix that maps unit source currents at each location to sensor potentials.

First used in L5.4 · Forward models

Leakage (source)

Also: source leakage, spatial leakage

Spread of an estimated source's activity into neighbouring source locations due to limited inverse resolution.

First used in L5.6 · Source-space connectivity and leakage

Leakage (spectral)

Also: spectral leakage

Spread of a signal's power into neighbouring frequency bins caused by finite window length and shape.

First used in L1.4 · Windowing, leakage and zero-padding

Linear mixed model

Also: LMM, mixed-effects model

Regression with fixed effects plus random effects that model variation across subjects or items.

First used in L6.2 · Mixed models and trial-level data

Montage

The set of channel derivations displayed or analysed; also the standard electrode-position layout.

First used in L0.2 · Electrodes, montages and the 10-20 system

Morlet wavelet

A sinusoid tapered by a Gaussian, defined by its centre frequency and number of cycles.

First used in L4.2 · STFT and Morlet wavelets

Multitaper

Spectral estimation that averages estimates from several orthogonal tapers to reduce variance.

First used in L4.3 · Multitaper and filter-Hilbert

Nyquist frequency

Half the sampling rate; the highest frequency that can be represented without aliasing.

First used in L1.1 · Sampling, Nyquist and aliasing

Passband

Also: passband / transition band / stopband

The frequency range a filter is designed to pass with little attenuation.

First used in L1.5 · Filters: FIR, IIR, and what they do to your data

Periodogram

The squared magnitude of a signal's DFT; an unbiased but high-variance spectral estimate.

First used in L1.3 · Power spectral density

Phase-amplitude coupling

Also: PAC

Dependence of a high-frequency amplitude on the phase of a lower-frequency rhythm.

First used in L4.5 · Phase, ITC and cross-frequency coupling

PLI

Also: phase lag index, PLV / PLI / wPLI

Asymmetry of the phase-difference distribution around zero; discards zero-lag interactions.

First used in L5.2 · Sensor-space connectivity

PLV

Also: phase-locking value, PLV / PLI / wPLI

Mean resultant length of the phase difference between two signals across time or trials.

First used in L5.2 · Sensor-space connectivity

Power spectral density

Also: PSD

Power per unit frequency, typically in µV²/Hz, as a function of frequency.

First used in L1.3 · Power spectral density

Rank (data)

Also: rank

The number of linearly independent channels; reduced by average referencing and interpolation.

First used in L2.2 · Channel locations and bad channels

Reference

The channel or combination of channels against which every potential is measured.

First used in L0.2 · Electrodes, montages and the 10-20 system

Ringing

Also: Gibbs phenomenon

Oscillatory artifact around sharp transients produced by a filter's impulse response.

First used in L1.5 · Filters: FIR, IIR, and what they do to your data

Standardized measurement error

Also: SME

The standard error of an ERP measurement for one participant, estimated by bootstrapping trials.

First used in L3.5 · SNR, trial counts and design

Stopband

Also: passband / transition band / stopband

The frequency range a filter is designed to attenuate.

First used in L1.5 · Filters: FIR, IIR, and what they do to your data

TFCE

Also: threshold-free cluster enhancement

Cluster-style enhancement of a statistic map that integrates over all thresholds instead of one.

First used in L4.7 · Statistics for time-frequency

Transition band

Also: transition bandwidth, passband / transition band / stopband

The frequency range over which a filter's response moves from passband to stopband.

First used in L1.5 · Filters: FIR, IIR, and what they do to your data

Volume conduction

Instantaneous spread of source currents through head tissues so that every sensor sees a mixture of sources.

First used in L0.1 · What EEG measures

Welch's method

Also: Welch

PSD estimation by averaging periodograms of overlapping, windowed segments.

First used in L1.3 · Power spectral density

wPLI

Also: weighted phase lag index, PLV / PLI / wPLI

PLI weighted by the magnitude of the imaginary cross-spectrum, reducing sensitivity to noise near zero lag.

First used in L5.2 · Sensor-space connectivity

Zero-phase filter

Also: zero-phase, forward-backward filtering, filtfilt

Filtering forward and backward so phase is unchanged; non-causal and spreads transients both ways.

First used in L1.5 · Filters: FIR, IIR, and what they do to your data