Individual Differences in Behavioral Estimates of Cochlear Nonlinearities

Abstract

Psychophysical methods provide a mechanism to infer the characteristics of basilar membrane responses in humans that cannot be directly measured. Because these behavioral measures are indirect, the interpretation of results depends on several underlying assumptions. Ongoing uncertainty about the suitability of these assumptions and the most appropriate measurement and compression estimation procedures, and unanswered questions regarding the effects of cochlear hearing loss and age on basilar membrane nonlinearities, motivated this experiment. Here, estimates of cochlear nonlinearities using temporal masking curves (TMCs) were obtained in a large sample of adults of various ages whose hearing ranged from normal to moderate cochlear hearing loss (Experiment 1). A wide range of compression slopes was observed, even for subjects with similar ages and thresholds, which warranted further investigation (Experiment 2). Potential sources of variance contributing to these individual differences were explored, including procedural-related factors (test-retest reliability, suitability of the linearreference TMC, probe sensation levels, and parameters of TMC fitting algorithms) and subject-related factors (age and age-related changes in temporal processing, strength of cochlear nonlinearities estimated with distortion-product otoacoustic emissions, estimates of changes in cochlear function from damage to outer hair cells versus inner hair cells). Subject age did not contribute significantly to TMC or compression slopes, and TMC slopes did not vary significantly with threshold. Test-retest reliability of TMCs suggested that TMC masker levels and the general shapes of TMCs did not change in a systematic way when re-measured many weeks later. Although the strength of compression decreased slightly with increasing hearing loss, the magnitude of individual differences in compression estimates makes it difficult to determine the effects of hearing loss and cochlear damage on basilar membrane nonlinearities in humans.

Level-Dependent Changes in Perception of Speech Envelope Cues

“…That is, more compression would result in "flatter" effective speech envelopes in the mid-level compressed region and greater changes to more "fluctuating" envelopes at lower and higher speech levels, where less compression of the envelope is expected. Greater envelope changes would predict steeper declines in recognition at lower and higher levels for subjects with more compression (Poling et al 2011;Horwitz et al 2012). Figure 5 displays scatterplots of slope values computed at 45 and 85 dB SPL, showing significant negative correlations for both consonants and key words (pG0.001 and p00.001, respectively).…”

“…Distortion-product otoacoustic emissions (DPOAEs) are assumed to reflect the physiological nonlinear cochlear process in humans with normal outer hair cell function (Dorn et al 2001;Neely et al 2009). Moreover, input-output functions derived from DPOAEs and psychophysical measures provide generally similar estimates of basilar-membrane response growth, given that both are characterized by a nearly linear segment for low levels and a compressive segment for moderate levels (e.g., Dorn et al 2001;Williams and Bacon 2005 (Poling et al 2011;Rodriguez et al 2011). In this experiment, DPOAEs and DPOAE input-output functions were measured to provide estimates of basilarmembrane nonlinearities for each subject, to compare and correlate with level-dependent changes observed in recognition of vocoded speech.…”

Computational Modeling of Individual Differences in Behavioral Estimates of Cochlear Nonlinearities

“…As described in Poling et al (2012), 51 subjects were divided into low (n=24; S1-S24; mean age=39.6 years; probe thresholds 13.2-22.2 dB SPL), mid (n=11; S25-S35; mean age=59.3 years; probe thresholds 23.9-34.2 dB SPL), and high (n=16; S36-S51; mean age=76.1 years; probe thresholds 41.0-57.7 dB SPL) threshold groups based on thresholds for the 20-ms, 1-kHz probe.…”

“…As discussed by Poling et al (2012), sources of individual differences among listeners with similar and different thresholds may include (1) the degree of hearing loss, (2) the contribution of outer (OHC) and inner (IHC) hair cell dysfunction to the hearing loss, (3) the degree of cochlear nonlinearity (i.e., compression), (4) the influence of the medial olivocochlear (MOC) reflex, (5) the ability to make use of stimulus cues for detecting the probe (i.e., detection efficiency), (6) the ratio of frequencies for on-and off-frequency maskers (i.e., the linear reference), (7) durations of the masker and probe (e.g., Lopez-Poveda et al 2003), (8) learning/practice effects, and (9) methods for fitting/ deriving compression. Some of the proposed sources of individual differences in compression estimates originate in a violation of the assumptions made when interpreting TMCs Oxenham 2009, 2010).…”

“…This study aimed to identify the primary sources of individual differences in TMCs in a large dataset of adults with normal and impaired hearing (Poling et al 2012) by predicting TMCs with a computational model of the auditory periphery (Zilany et al 2009). This model, when expanded to include the processes of temporal integration and detection, is effective at predicting masking thresholds and is capable of simulating effects of hearing loss, the contribution of OHC and IHC dysfunction, nonlinearity of the off-frequency reference, and detection efficiency.…”