Investigating time-efficiency of forward masking paradigms for estimating basilar membrane input-output characteristics.

It is well known that pure-tone audiometry does not sufficiently describe individual hearing loss (HL) and that additional measures beyond pure-tone sensitivity might improve the diagnostics of hearing deficits. Specifically, forward masking experiments to estimate basilar-membrane (BM) input-output (I/O) function have been proposed. However, such measures are very time consuming. The present study investigated possible modifications of the temporal masking curve (TMC) paradigm to improve time and measurement efficiency. In experiment 1, estimates of knee point (KP) and compression ratio (CR) of individual BM I/Os were derived without considering the corresponding individual "off-frequency" TMC. While accurate estimation of KPs was possible, it is difficult to ensure that the tested dynamic range is sufficient. Therefore, in experiment 2, a TMC-based paradigm, referred to as the "gap method", was tested. In contrast to the standard TMC paradigm, the maker level was kept fixed and the "gap threshold" was obtained, such that the masker just masks a low-level (12 dB sensation level) signal. It is argued that this modification allows for better control of the tested stimulus level range, which appears to be the main drawback of the conventional TMC method. The results from the present study were consistent with the literature when estimating KP levels, but showed some limitations regarding the estimation of the CR values. Perspectives and limitations of both approaches are discussed.

Refining a model of hearing impairment using speech psychophysics.

The premise of this study is that models of hearing, in general, and of individual hearing impairment, in particular, can be improved by using speech test results as an integral part of the modeling process. A conceptual iterative procedure is presented which, for an individual, considers measures of sensitivity, cochlear compression, and phonetic confusions using the Diagnostic Rhyme Test (DRT) framework. The suggested approach is exemplified by presenting data from three hearing-impaired listeners and results obtained with models of the hearing impairment of the individuals. The work reveals that the DRT data provide valuable information of the damaged periphery and that the non-speech and speech data are complementary in obtaining the best model for an individual.

Simulating psychophysical tuning curves in listeners with dead regions.

OBJECTIVE: This study investigates the relation between diagnosis of dead regions based on the off-frequency psychophysical tuning curve (PTC) tip and the frequency and level of the probe tone. DESIGN: A previously developed functional model of auditory processing was used to simulate the complete loss of inner hair cells (IHC), dysfunction of outer hair cells (OHC), complete loss of IHCs in combination with OHC dysfunction, and IHC insensitivity. The model predictions were verified through comparison with experimental data. STUDY SAMPLE: This study compares PTC data of five normal-hearing listeners and six hearing-impaired listeners with model-simulated PTC data. RESULTS: It was shown that OHC activity and IHC insensitivity may significantly alter the shift of PTC tips with increasing probe level. CONCLUSIONS: Model results suggest that OHC activity and IHC insensitivity can change the outcome of dead region diagnosis using PTCs. Supplementary to PTC dead region diagnostic information, model results may provide additional information regarding the edge frequency of a dead region and OHC function.

Characterizing auditory processing and perception in individual listeners with sensorineural hearing loss.

This study considered consequences of sensorineural hearing loss in ten listeners. The characterization of individual hearing loss was based on psychoacoustic data addressing audiometric pure-tone sensitivity, cochlear compression, frequency selectivity, temporal resolution, and intensity discrimination. In the experiments it was found that listeners with comparable audiograms can show very different results in the supra-threshold measures. In an attempt to account for the observed individual data, a model of auditory signal processing and perception [Jepsen et al., J. Acoust. Soc. Am. 124, 422-438 (2008)] was used as a framework. The parameters of the cochlear processing stage of the model were adjusted to account for behaviorally estimated individual basilar-membrane input-output functions and the audiogram, from which the amounts of inner hair-cell and outer hair-cell losses were estimated as a function of frequency. All other model parameters were left unchanged. The predictions showed a reasonably good agreement with the measured individual data in the frequency selectivity and forward masking conditions while the variation of intensity discrimination thresholds across listeners was underestimated by the model. The model and the associated parameters for individual hearing-impaired listeners might be useful for investigating effects of individual hearing impairment in more complex conditions, such as speech intelligibility in noise.

Effects of pulsing of the target tone on the audibility of partials in inharmonic complex tones.

The audibility of partials was measured for complex tones with partials uniformly spaced on an ERB(N)-number scale. On each trial, subjects heard a sinusoidal "probe" followed by a complex tone. The probe was mistuned downwards or upwards (at random) by 3% or 4.5% from the frequency of one randomly selected partial in the complex (the "target"). The subject indicated whether the target was higher or lower in frequency than the probe. The probe and the target were pulsed on and off and the ramp times and inter-pulse intervals were systematically varied. Performance was better for longer ramp times and longer inter-pulse intervals. In a second experiment, the ability to detect which of two complex tones contained a pulsed partial was measured. The pattern of results was similar to that for experiment 1. A model of auditory processing including an adaptation stage was able to account for the general pattern of the results of experiment 2. The results suggest that the improvement in ability to hear out a partial in a complex tone produced by pulsing that partial is partly mediated by a release from adaptation produced by the pulsing, and does not result solely from reduction of perceptual confusion.

A computational model of human auditory signal processing and perception.

A model of computational auditory signal-processing and perception that accounts for various aspects of simultaneous and nonsimultaneous masking in human listeners is presented. The model is based on the modulation filterbank model described by Dau et al. [J. Acoust. Soc. Am. 102, 2892 (1997)] but includes major changes at the peripheral and more central stages of processing. The model contains outer- and middle-ear transformations, a nonlinear basilar-membrane processing stage, a hair-cell transduction stage, a squaring expansion, an adaptation stage, a 150-Hz lowpass modulation filter, a bandpass modulation filterbank, a constant-variance internal noise, and an optimal detector stage. The model was evaluated in experimental conditions that reflect, to a different degree, effects of compression as well as spectral and temporal resolution in auditory processing. The experiments include intensity discrimination with pure tones and broadband noise, tone-in-noise detection, spectral masking with narrow-band signals and maskers, forward masking with tone signals and tone or noise maskers, and amplitude-modulation detection with narrow- and wideband noise carriers. The model can account for most of the key properties of the data and is more powerful than the original model. The model might be useful as a front end in technical applications.