Abstract
Phase-amplitude coupling is a promising construct to study cognitive processes in electroencephalography (EEG) and magnetencephalography (MEG). Due to the novelty of the concept, various measures are used in the literature to calculate phase-amplitude coupling. Here, performance of the three most widely used phase-amplitude coupling measures – phase-locking value (PLV), mean vector length (MVL), and modulation index (MI) – is thoroughly compared with the help of simulated data. We combine advantages of previous reviews and use a realistic data simulation, examine moderators and provide inferential statistics for the comparison of all three indices of phase-amplitude coupling. Our analyses show that all three indices successfully differentiate coupling strength and coupling width when monophasic coupling is present. While the mean vector length was most sensitive to modulations in coupling strengths and width, biphasic coupling can solely be detected by the modulation index. Coupling values of all three indices were influenced by moderators including data length, signal-to-noise-ratio, and sampling rate when approaching Nyquist frequencies. The modulation index was most robust against confounding influences of these moderators. Based on our analyses, we recommend the modulation index for noisy and short data epochs with unknown forms of coupling. For high quality and long data epochs with monophasic coupling and a high signal-to-noise ratio, the use of the mean vector length is recommended. Ideally, both indices are reported simultaneously for one data set.
Highlights
mean vector length is most sensitive for differentiating coupling strength
modulation index is most robust to differences in data length, sampling rate and SNR
phase-locking value and mean vector length cannot detect biphasic phase-amplitude coupling
Footnotes
E-mail addresses: naumann{at}uni-trier.de (E. Naumann), bjoern.rasch{at}unifr.ch (B. Rasch)
Declaration of interest: none.
Abbreviation: EEG: electroencephalography, MEG: magnetencephalography, PLV: phase-locking value, MVL: mean vector length, MI: modulation index, FFT: Fast Fourier transform, SI: synchronization index, ESC: envelope-to-signal correlation, BA: phase binning combined with ANOVA, wPLF: weighted phase locking factor, GLM: general linear model, FIR: finite impulse response, ANOVA: analysis of variance, S. D.: standard deviation, SEM: standard error, CFC: cross-frequency coupling
Funding: This project has received funding from the Research Focus “Psychobiology of Stress” within the research initiative of the state Rhineland-Palatinate by the Ministry of Science and from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement n° 677875). Both funding Institutions had no further role in the study design, the collection, analysis, and interpretation of data, the writing of the manuscript, and the decision to submit the paper for publication. The work was performed at Trier University, Faculty I - Psychology, Department of General Psychology and Methodology.
