Forward entrainment: Psychophysics, neural correlates, and function

Abstract

We define forward entrainment as that part of behavioral or neural entrainment that outlasts the entraining stimulus. In this review, we examine conditions under which one may optimally observe forward entrainment. In Part 1, we review and evaluate studies that have observed forward entrainment using a variety of psychophysical methods (detection, discrimination, and reaction times), different target stimuli (tones, noise, and gaps), different entraining sequences (sinusoidal, rectangular, or sawtooth waveforms), a variety of physiological measures (MEG, EEG, ECoG, CSD), in different modalities (auditory and visual), across modalities (audiovisual and auditory-motor), and in different species. In Part 2, we describe those experimental conditions that place constraints on the magnitude of forward entrainment, including an evaluation of the effects of signal uncertainty and attention, temporal envelope complexity, signal-to-noise ratio (SNR), rhythmic rate, prior experience, and intersubject variability. In Part 3 we theorize on potential mechanisms and propose that forward entrainment may instantiate a dynamic auditory afterimage that lasts a fraction of a second to minimize prediction error in signal processing.

Keywords: Attention; Entrainment; Periodicity; Phase; Signal detection.

Fig. 1

Results from four psychophysical studies that have shown multicycle forward entrainment. Top two panels show results from auditory tasks, and bottom two from vision tasks. Left panels show an in-phase pattern of forward entrainment and right panels show an antiphasic pattern

Fig. 2

Results from four studies that have shown forward entrainment using reaction-time (RT) measures in four different auditory tasks (gap detection, pitch identification, motion paradigm, and tone detection). See text for a detailed explanation of each study

Fig. 3

Four neurophysiological studies of forward entrainment using four different measurement methods (ECoG, EEG, CSD, and MEG). See text for details. Permission to use granted by Elsevier under STM (The International Association of Scientific, Technical and Medical Publishers) permission guidelines, and by The Journal of Neuroscience and Nature Communications under the terms of the Creative Commons Attribution 4.0 International License

Fig. 4

Top: Performance as a function of signal temporal position averaged across subjects. Time zero represents the end of the entraining stimulus. The parameter is signal-to-noise ratio (SNR), with the 3.5-dB condition showing data reported by Hickok et al. (2015). Bottom: Psychometric functions estimated from data in the top panel (arrows). Red and blue curves show functions generate from data marked by arrows of the same colors in the top panel. These arrows designate the peaks and dips of the curve at 3.5 dB in the top panel (orange), which is antiphasic to dips and peaks of the stimulus modulation envelope (had it continued). The blue curve is associated with the expected dips in the AM noise stimulus, and the red curve with the expected peaks. See text for details