Cochlear gain loss can compensate for temporal coding deficits in AM detection

Evidence

The present study offers a window into how cochlear neuropathy and cochlear gain loss interact to affect perception of fast temporal modulations important for speech perception in adverse conditions. AM detection thresholds and EFR strength to 100 % modulated stimuli were normal in the mild HI listeners we tested. These findings are in line with other studies that show normal AM detection thresholds (Moore et al. 1996 ) and EFR strengths (Zhong et al. 2014 ) for subjects with elevated hearing thresholds. However, interactions between hearing deficits were apparent from correlating the psychoacoustic results with objective measures in the same listeners. Whereas AM detection for NH listeners was correlated to their EFR slopes as a measure for temporal coding fidelity, cochlear gain loss was shown to compensate for reduced temporal coding in the HI listeners to yield near normal AM detection thresholds. — Dijk, Pim van, Physiology, Psychoacoustics and…, 5904

Figure 2 shows the psychoacoustic AM detection thresholds in quiet and in the presence of broadband (panel A) and narrowband noise (panel B). Average AM detection thresholds were similar for NH and mild HI listeners supporting the observation that temporal modulation detection is not determined by the hearing threshold (Moore et al. 1996 ). In fact, the variation in thresholds for the NH listeners was significantly correlated to the EFR slope metric (panel C) demonstrating that temporal coding fidelity predicts performance when hearing thresholds are normal (see also Bharadwaj et al. 2015 ). For the mild HI listeners, this relationship is more complex as the reduced temporal coding fidelity in those listeners (i.e., only 2 out of 6 listeners had EFR responses down to ‑4 dB AM depth) would predict worse AM detection thresholds. The observation that HI listeners had normal AM performance despite their reduced temporal coding fidelity suggests that cochlear gain loss can compensate for temporal coding deficits to yield normal AM detection thresholds. — Dijk, Pim van, Physiology, Psychoacoustics and…, 5891

However, interactions between hearing deficits were apparent from correlating the psychoacoustic results with objective measures in the same listeners. Whereas AM detection for NH listeners was correlated to their EFR slopes as a measure for temporal coding fidelity, cochlear gain loss was shown to compensate for reduced temporal coding in the HI listeners to yield near normal AM detection thresholds. — Dijk, Pim van, Physiology, Psychoacoustics and…, 5903

Categorization

• DEFINE: EFR (envelope following response) and AM detection thresholds defined implicitly as objective and psychoacoustic measures of temporal coding.
• XREF: Connects to the broader theme of cochlear neuropathy hidden behind normal audiograms — hidden hearing loss literature. — connects to: Hearing-impaired listeners fail to gain temporal resolution in background noise — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1933; Standard signal-detection measures fail for time-evolving detection tasks — Dijk, Pim van, Physiology, Psychoacoustics and…, 3327; Cochlear neuropathy and gain loss may push AM detection in opposite directions — Dijk, Pim van, Physiology, Psychoacoustics and…, 5873 (+4 more)
• QUESTION: What is the mechanism by which cochlear gain loss compensates? Does the reduced gain flatten the effective dynamic range and thereby improve envelope coding relative to internal noise?
• corroborated: 8 independent passages support this claim — Dijk, Pim van, Physiology, Psychoacoustics and…, 5904; Dijk, Pim van, Physiology, Psychoacoustics and…, 5891; Dijk, Pim van, Physiology, Psychoacoustics and…, 5903

Broader Connections

• Cochlear compression may protect AM detection against added background noise #expands (0.82)
• Differential metrics can separate cochlear gain loss from temporal coding deficits in hearing loss #corroborates (0.80) — Dijk, Pim van, Physiology, Psychoacoustics and…, 5870