Volume 119, Issue 1, January 2006
Index of content:
- PHYSIOLOGICAL ACOUSTICS 
119(2006); http://dx.doi.org/10.1121/1.2141296View Description Hide Description
The construction, measurement, and modeling of an artificial cochlea (ACochlea) are presented in this paper. An artificial basilar membrane (ABM) was made by depositing discrete Cubeams on a piezomembrane substrate. Rather than two fluid channels, as in the mammalian cochlea, a single fluid channel was implemented on one side of the ABM, facilitating the use of a laser to detect the ABM vibration on the other side. Measurements were performed on both the ABM and the ACochlea. The measurement results on the ABM show that the longitudinal coupling on the ABM is very strong. Reduced longitudinal coupling was achieved by cutting the membrane between adjacent beams using a laser. The measured results from the ACochlea with a laser-cut ABM demonstrate cochlear-like features, including traveling waves, sharp high-frequency rolloffs, and place-specific frequency selectivity. Companion computational models of the mechanical devices were formulated and implemented using a circuit simulator. Experimental data were compared with simulation results. The simulation results from the computational models of the ABM and the ACochlea are similar to their experimental counterparts.
119(2006); http://dx.doi.org/10.1121/1.2139628View Description Hide Description
A computer model of the auditory periphery was used to address the question of what constitutes the physiological substrate of absolute auditory threshold. The model was first evaluated to show that it is consistent with experimental findings that auditory-nerve fiber spikes can be predicted to occur when the running integral of stimulus pressure reaches some critical value [P. Heil and H. Neubauer, J. Neurosci.15, 7404–7415 (2001)]. It was then modified to examine two ways in which the accumulation and clearance of receptor presynaptic calcium might explain this effect. Both methods gave results that matched the animal data. It was also shown how the rate of clearance of presynaptic calcium could be used to explain the origin of differences between low and high spontaneous-rate fiber types. When spiking activity is aggregated across a number of similar high spontaneous-rate fibers and used as the input to a model of a cochlear nucleus coincidence neuron, its response can be used to judge whether or not a stimulus is present. A simulated psychophysical experiment then demonstrated that this simple decision procedure can reproduce measurements of absolute auditory threshold for tones in quiet where the threshold is a joint function of both time and level.
Influence of primary-level and primary-frequency ratios on human distortion product otoacoustic emissionsa)119(2006); http://dx.doi.org/10.1121/1.2133714View Description Hide Description
The combined influence of primary-level differences and primary-frequency ratio on distortion product otoacoustic emission (DPOAE) level was investigated in 20 normal-hearing subjects. DPOAEs were recorded with continuously varying stimulus levels [Neely et al.J. Acoust. Soc. Am.117, 1248–1259 (2005)] for the following stimulus conditions: , 2, 4, and and to 1.4; various , including one individually optimized to produce the largest DPOAE. For broadly spaced primary frequencies at low levels, the largest DPOAEs were recorded when was much higher than , with remaining relatively constant as increased. As decreased, the largest DPOAEs were observed when was closer to and increased as increased. Optimal values for and were derived from these data. In general, average DPOAE levels for the new and were equivalent to or larger than those observed for other stimulus combinations, including the described by Kummer et al. [J. Acoust. Soc. Am.103, 3431–3444 (1998)] and those defined by Neely et al. in which was evaluated, but was fixed at 1.2.
Signal-to-noise ratio and frequency analysis of continuous loop averaging deconvolution (CLAD) of overlapping evoked potentials119(2006); http://dx.doi.org/10.1121/1.2133682View Description Hide Description
In this study, a frequency domain formulation of continuous loop averaging deconvolution (CLAD) of overlapping evoked potentials is developed and applied for the extraction of transient responses from recordings obtained at high stimulation rates. This formulation allows for a faster execution of CLAD by using fast Fourier transform algorithms. The frequency characteristics of the deconvolution filter depends exclusively on the stimulus sequence and determines whether the noncoherent noise is amplified or attenuated in different frequencies. A formula for calculating the signal-to-noise ratio (SNR) achieved by the deconvolution process is developed. The newly developed theory and the methodology is applied to the extraction of the auditory brainstem and middle latency responses using various sequences. The effects of the sequence used and the number of sweeps averaged in ongoing acquisition on SNR are examined by using single sweep recordings. The results verify the deconvolution theory and the methodology and show its limitations. Depending on the frequency characteristics of the sequence, the deconvolution process can amplify or attenuate the EEG noise. Proper selection of the stimulus sequence can increase the SNR enhancement obtained with conventional averaging.
119(2006); http://dx.doi.org/10.1121/1.2139068View Description Hide Description
We investigated how morphological differences in the auditory periphery of teleost fishes may relate to hearing capabilities. Two species of western Atlantic sciaenids were examined: weakfish (Cynoscion regalis, Block and Schneider) and spot (Leiostomus xanthurus, Lacepede). These species differ in the anatomical relationship between the swim bladder and the inner ear. In weakfish, the swim bladder has a pair of anterior horns that terminate close to the ear, while there are no extensions of the swim bladder in spot. Thus, the swim bladder in spot terminates at a greater distance from the ear when compared to weakfish. With the use of the auditory brainstem response technique, Cynoscion regalis were found to detect frequencies up to , while Leiostomus xanthurusdetected up to . There were, however, no significant interspecific differences in auditory sensitivity for stimuli between 200 and . These data support the hypothesis that the swim bladder can potentially expand the frequency range of detection.