A comparison of spectral magnitude and phase-locking value analyses of the frequency-following response to complex tones

Abstract

Two experiments, both presenting diotic, harmonic tone complexes (100 Hz fundamental), were conducted to explore the envelope-related component of the frequency-following response (FFR ENV ), a measure of synchronous, subcortical neural activity evoked by a periodic acoustic input. Experiment 1 directly compared two common analysis methods, computing the magnitude spectrum and the phase-locking value (PLV). Bootstrapping identified which FFR ENV frequency components were statistically above the noise floor for each metric and quantified the statistical power of the approaches. Across listeners and conditions, the two methods produced highly correlated results. However, PLV analysis required fewer processing stages to produce readily interpretable results. Moreover, at the fundamental frequency of the input, PLVs were farther above the metric's noise floor than spectral magnitudes. Having established the advantages of PLV analysis, the efficacy of the approach was further demonstrated by investigating how different acoustic frequencies contribute to FFR ENV , analyzing responses to complex tones composed of different acoustic harmonics of 100 Hz (Experiment 2). Results show that the FFR ENV response is dominated by peripheral auditory channels responding to unresolved harmonics, although low-frequency channels driven by resolved harmonics also contribute. These results demonstrate the utility of the PLV for quantifying the strength of FFR ENV across conditions.

Individual Differences Reveal Correlates of Hidden Hearing Deficits

“…Given that neuropathy from both noise exposure and aging preferentially (though by no means exclusively) impacts low-SR fibers (Fig. 2), we hypothesized that such stimuli would increase the likelihood of exposing suprathreshold temporal coding deficits resulting from neuropathy (Bharadwaj et al, 2014). We measured peripheral/cochlear processing of sounds using distortion-product otoacoustic emissions (DPOAEs; Johnson et al, 2006), psychophysical tuning curves (Oxenham and Shera 2003), and audiometric detection thresholds.…”

“…We measured peripheral/cochlear processing of sounds using distortion-product otoacoustic emissions (DPOAEs; Johnson et al, 2006), psychophysical tuning curves (Oxenham and Shera 2003), and audiometric detection thresholds. We measured early neural coding of temporal information using subcortical envelope-following responses (EFRs) (Bharadwaj and Shinn-Cunningham, 2014;Bharadwaj et al, 2014). We then compared these measures to perceptual estimates of temporal sensitivity, to electroencephalography (EEG)-based measures of cortical representation of acoustic spatial features (Salminen et al, 2010), and to selective attention performance in a complex speechon-speech masking task.…”

“…The stimulus level was set at 75 dB SPL. Off-frequency notched-noise (notch width of 800 Hz) maskers, realized independently in each trial and uncorrelated across the two ears, were presented at a signal-to-noise ratio Zilany et al, 2014) in quiet (top) and with additive restaurant chatter (bottom) for a short analysis time window across fibers with different characteristic frequencies (CFs). Although strong modulations are apparent in both cases, the latter shows more irregularities.…”

“…We hypothesize that cochlear neuropathy underlies a portion of individual differences in temporal coding fidelity. Modeling the EFR as a summed response over a population of (model) inferior colliculus cells, Bharadwaj et al (2014) suggested that (1) stimuli at high levels and shallow modulation depths should accentuate the contributions of low-SR fibers, and that (2) changes in EFR amplitude with modulation depth would provide an easy-to-interpret, self-normalized measure of suprathreshold coding fidelity.…”

“…Furthermore, significant levels of deafferentation do not appear to affect detection thresholds (Schuknecht and Woellner, 1955;Lobarinas et al, 2013); however, in the healthy auditory system, convergence of nerve fibers is important for precise coding of both temporal finestructure and envelope cues in suprathreshold sounds (Joris et al, 1994;Lopez-Poveda and Barrios, 2013). Given the importance of temporal information for speech perception (Zeng et al, 2005), source localization (Blauert, 1997), grouping of acoustic elements into perceptual objects (Darwin, 1997;Shamma et al, 2011), and release from masking (Moore, 2008;Christiansen et al, 2013), degraded temporal coding is likely to interfere with suprathreshold perceptual ability-a form of "hidden hearing loss" (Bharadwaj et al, 2014;Plack et al, 2014).…”