title: Statistically significant contrasts between EMG waveforms revealed using wavelet-based functional ANOVA.
abstract: We developed wavelet-based functional ANOVA (wfANOVA) as a novel approach for comparing neurophysiological signals that are functions of time. Temporal resolution is often sacrificed by analyzing such data in large time bins, increasing statistical power by reducing the number of comparisons. We performed ANOVA in the wavelet domain because differences between curves tend to be represented by a few temporally localized wavelets, which we transformed back to the time domain for visualization. We compared wfANOVA and ANOVA performed in the time domain (tANOVA) on both experimental electromyographic (EMG) signals from responses to perturbation during standing balance across changes in peak perturbation acceleration (3 levels) and velocity (4 levels) and on simulated data with known contrasts. In experimental EMG data, wfANOVA revealed the continuous shape and magnitude of significant differences over time without a priori selection of time bins. However, tANOVA revealed only the largest differences at discontinuous time points, resulting in features with later onsets and shorter durations than those identified using wfANOVA (P < 0.02). Furthermore, wfANOVA required significantly fewer (~1/4;×; P < 0.015) significant F tests than tANOVA, resulting in post hoc tests with increased power. In simulated EMG data, wfANOVA identified known contrast curves with a high level of precision (r(2) = 0.94 ± 0.08) and performed better than tANOVA across noise levels (P < <0.01). Therefore, wfANOVA may be useful for revealing differences in the shape and magnitude of neurophysiological signals (e.g., EMG, firing rates) across multiple conditions with both high temporal resolution and high statistical power.
authors.affiliation: The Wallace H. Coulter Department of Biomedical Engineering, Emory University and the Georgia Institute of Technology, Atlanta, Georgia 30332-0535, USA.
authors.forename: J Lucas
authors.initials: JL
authors.lastname: McKay
authors.forename: Torrence D J
authors.initials: TD
authors.lastname: Welch
authors.forename: Brani
authors.initials: B
authors.lastname: Vidakovic
authors.forename: Lena H
authors.initials: LH
authors.lastname: Ting
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D003198:Computer Simulation; D004576:Electromyography / Q000379:methods; D006801:Humans; D018482:Muscle, Skeletal / Q000502:physiology*; D013997:Time Factors; D058067:Wavelet Analysis