Relation Between Cochlear Mechanics and Performance of Temporal Fine Structure-Based Tasks

Abstract

This study examined whether the mechanical characteristics of the cochlea could influence individual variation in the ability to use temporal fine structure (TFS) information. Cochlear mechanical functioning was evaluated by swept-tone evoked otoacoustic emissions (OAEs), which are thought to comprise linear reflection by micromechanical impedance perturbations, such as spatial variations in the number or geometry of outer hair cells, on the basilar membrane (BM). Low-rate (2 Hz) frequency modulation detection limens (FMDLs) were measured for carrier frequency of 1000 Hz and interaural phase difference (IPD) thresholds as indices of TFS sensitivity and highrate (16 Hz) FMDLs and amplitude modulation detection limens (AMDLs) as indices of sensitivity to non-TFS cues. Significant correlations were found among low-rate FMDLs, low-rate AMDLs, and IPD thresholds (R = 0.47-0.59). A principal component analysis was used to show a common factor that could account for 81.1, 74.1, and 62.9 % of the variance in low-rate FMDLs, low-rate AMDLs, and IPD thresholds, respectively. An OAE feature, specifically a characteristic dip around 2-2.5 kHz in OAE spectra, showed a significant correlation with the common factor (R = 0.54). High-rate FMDLs and AMDLs were correlated with each other (R = 0.56) but not with the other measures. The results can be interpreted as indicating that (1) the low-rate AMDLs, as well as the IPD thresholds and low-rate FMDLs, depend on the use of TFS information coded in neural phase locking and (2) the use of TFS information is influenced by a particular aspect of cochlear mechanics, such as mechanical irregularity along the BM.

The role of cochlear place coding in the perception of frequency modulation

“…This finding likely extends to simple frequency discrimination, which is believed to rely on the same mechanism as slow FM (Sęk and Moore, 1995). A unitary code for FM and AM at all rates also helps explain the generally high-multicollinearity between FM and AM sensitivity observed here ( Figure 3) and in several previous studies with normal-hearing listeners (Whiteford and Oxenham, 2015;Otsuka et al, 2016;Paraouty and Lorenzi, 2017;, although the effect size of the correlation between slow-rate FM and AM was smaller than observed in previous studies. It may also help explain why attempts to improve speech and music perception by reintroducing fine timing cues via electrical pulses in cochlear implants have not been successful (Zeng et al, 2005;Schatzer et al, 2010).…”

“…Another alternative interpretation is that a dual code, based on combined place and timing cues, accounts for slow FM sensitivity, rather than a unitary code. A dual code could potentially explain the high collinearity often observed between measures of FM and AM sensitivity (Whiteford and Oxenham, 2015;Otsuka et al, 2016;Paraouty and Lorenzi, 2017;, as well as the observation from experiment 1 that slow-rate FM sensitivity may not be as strongly correlated to AM sensitivity as fast-rate FM (although these differences in correlation strength were not statistically significant). In addition, it has been found that AM can interfere with the detection of FM, particularly at fast rates and high carrier frequencies, perhaps pointing to the possibility of a dual code (Moore and Sęk, 1996;Ernst and Moore, 2010;King et al, 2019).…”

Assessing the Role of Place and Timing Cues in Coding Frequency and Amplitude Modulation as a Function of Age

“…A few recent studies have used correlational measures in NH listeners to examine what peripheral code may be responsible for low-frequency carrier FM and have found conflicting evidence for the presence of TFS coding (e.g., Whiteford and Oxenham 2015;Otsuka et al 2016;Paraouty and Lorenzi 2017). These studies have revealed high multicollinearity across modulation-detection tasks, including those thought to use separate mechanisms (e.g., low-carrier, slowrate FM, and slow-rate AM).…”

The Physiologic and Psychophysical Consequences of Severe-to-Profound Hearing Loss

“…TE is coded in the cochlea as the probability of auditory neuron firing given the amplitude of displacement at a cochlear place, and phase locking to the TE has been observed throughout the cochlea and maintained to the auditory cortex. 74,75 Information in acoustic signals is conveyed primarily through changes in amplitude as a function of frequency over time, and TE represents this information after an initial stage of cochlear filtering. Many basic auditory features rely on TE local to a specific frequency region, including loudness, pitch and source location, and auditory object formation.…”