Morten Løve Jepsen

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.

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.

Simulating psychophysical tuning curves in listeners with dead regions

Abstract 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.

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.

Estimating the basilar‐membrane input/output‐function in normal‐hearing and hearing‐impaired listeners using forward masking

To partly characterize the function of cochlear processing in humans, the basilar membrane (BM) input‐output (I/O) function can be estimated. In recent studies, forward masking has been used to estimate BM compression. If an on‐frequency masker is processed compressively, while an off‐frequency masker is transformed more linearly, the ratio between the slopes of growth of masking (GOM) functions provides an estimate of BM compression at the signal frequency. In this study, this paradigm is extended to also estimate the knee‐point of the I/O‐function between linear processing at low levels and compressive processing at medium levels. If a signal can be masked by a low‐level on‐frequency masker such that signal and masker fall in the linear region of the I/O‐function, then a steeper GOM function is expected. The knee‐point can then be estimated in the input level region where the GOM changes significantly. Data were collected from eight normal‐hearing (NH) and five hearing‐impaired (HI) listeners with mild to moderate sensorineural hearing loss. Both groups showed large inter‐subject but low intra‐subject variability. When the knee‐point could be estimated for the HI listeners it was shifted towards higher input levels and compression was similar to that of NH listeners.

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.

Efficient estimates of cochlear hearing loss parameters in individual listeners

It has been suggested that the level corresponding to the knee-point of the basilar membrane (BM) input/output (I/O) function can be used to estimate the amount of inner- and outer hair-cell loss (IHL, OHL) in listeners with a moderate cochlear hearing impairment Plack et al. (2004). According to Jepsen and Dau (2011) IHL + OHL = HLT [dB], where HLT stands for total hearing loss. Hence having estimates of the total hearing loss and OHC loss, one can estimate the IHL. In the present study, results from forward masking experiments based on temporal masking curves (TMC; Nelson et al., 2001) are presented and used to estimate the knee-point level and the compression ratio of the I/O function. A time-efficient paradigm based on the single-interval-up-down method (SIUD; Lecluyse and Meddis (2009)) was used. In contrast with previous studies, the present study used only on-frequency TMCs to derive estimates of the knee-point level. Further, it is explored whether it is possible to estimate the compression ratio ...

A physiologically inspired model of auditory stream segregation based on a temporal coherence analysis

The ability to perceptually separate acoustic sources and focus ones attention on a single source at a time is essential for our ability to use acoustic information. In this study, a physiologically inspired model of human auditory processing [M. L. Jepsen and T. Dau, J. Acoust. Soc. Am. 124, 422-438, (2008)] was used as a front end of a model for auditory stream segregation. A temporal coherence analysis [M. Elhilali, C. Ling, C. Micheyl, A. J. Oxenham and S. Shamma, Neuron. 61, 317-329, (2009)] was applied at the output of the preprocessing, using the coherence across tonotopic channels to group activity across frequency. Using this approach, the described model is able to quantitatively account for classical streaming phenomena relying on frequency separation and tone presentation rate, such as the temporal coherence boundary and the fission boundary [L. P. A. S. van Noorden, doctoral dissertation, Institute for Perception Research, Eindhoven, NL, (1975)]. The same model also accounts for the perceptu...