Volume 120, Issue 3, September 2006
Index of content:
- PHYSIOLOGICAL ACOUSTICS 
120(2006); http://dx.doi.org/10.1121/1.2225858View Description Hide Description
To better understand how the auditory system extracts speech signals in the presence of noise,discrimination thresholds for the second formant frequency were predicted with simulations of auditory-nerve responses. These predictions employed either average-rate information or combined rate and timing information, and either populations of model fibers tuned across a wide range of frequencies or a subset of fibers tuned to a restricted frequency range. In general, combined temporal and rate information for a small population of model fibers tuned near the formant frequency was most successful in replicating the trends reported in behavioral data for formant-frequency discrimination. To explore the nature of the temporal information that contributed to these results, predictions based on model auditory-nerve responses were compared to predictions based on the average rates of a population of cross-frequency coincidence detectors. These comparisons suggested that average response rate (count) of cross-frequency coincidence detectors did not effectively extract important temporal information from the auditory-nerve population response. Thus, the relative timing of action potentials across auditory-nerve fibers tuned to different frequencies was not the aspect of the temporal information that produced the trends in formant-frequency discrimination thresholds.
Modeling auditory-nerve responses for high sound pressure levels in the normal and impaired auditory periphery120(2006); http://dx.doi.org/10.1121/1.2225512View Description Hide Description
This paper presents a computational model to simulate normal and impaired auditory-nerve (AN) fiber responses in cats. The model responses match physiological data over a wider dynamic range than previous auditory models. This is achieved by providing two modes of basilar membrane excitation to the inner hair cell (IHC) rather than one. The two modes are generated by two parallel filters, component 1 (C1) and component 2 (C2), and the outputs are subsequently transduced by two separate functions. The responses are then added and passed through the IHC low-pass filter followed by the IHC-AN synapsemodel and discharge generator. The C1 filter is a narrow-band, chirp filter with the gain and bandwidth controlled by a nonlinear feed-forward control path. This filter is responsible for low and moderate level responses. A linear, static, and broadly tuned C2 filter followed by a nonlinear, inverted and nonrectifying C2 transduction function is critical for producing transition region and high-level effects. Consistent with Kiang’s two-factor cancellation hypothesis, the interaction between the two paths produces effects such as the C1/C2 transition and peak splitting in the period histogram. The model responses are consistent with a wide range of physiological data from both normal and impaired ears for stimuli presented at levels spanning the dynamic range of hearing.
120(2006); http://dx.doi.org/10.1121/1.2221415View Description Hide Description
Although numerous studies have investigated temporal integration of the acoustic-reflex threshold (ART), research is lacking on the effect of age on temporal integration of the ART. Therefore the effect of age on temporal integration of the ART was investigated for a broad-band noise (BBN) activator. Subjects consisted of two groups of adults with normal-hearing sensitivity: one group of 20 young adults (ten males and ten females, ages , with a mean age of ) and one group of 20 older adults (ten males and ten females, ages , with a mean age of ). Activating stimulus durations were 12, 25, 50, 100, 200, 300, 500, and . Significant main effects for duration and age were obtained. That is, as the duration increased, the acoustic reflex threshold for BBN decreased. The interactions of group and level were not significant. The result of pair-wise analysis indicated statistically significant differences between the two age groups at durations of and longer. The observed age effect on temporal integration of the ART for the BBN activator is interpreted in relation to senescent changes in the auditory system.