摘要:

The ultrasonic attenuation of skimmed milk, of the serum containing the soluble whey proteins and small casein aggregates and of ultrafiltered serum was measured in the frequency range 15–96 MHz. From these measurements the attenuation due to the colloidal casein micelles in serum was obtained. For the serum, α∝f1.86±0.02; for the soluble proteins, Δα∝f1.16±0.04; and for the casein micelles, Δα∝f1.06±0.05. The ultrasonic attenuation of the soluble proteins is similar to that of other protein solutions; however, ultrasonic attenuation of the casein micelles differed from that of the soluble proteins. Using the theory of Allegra and Hawley [J. Acoust. Soc. Am.36, 1545–1564 (1972)] for the ultrasonic attenuation of suspensions of elastic spheres, the expected attenuation for a model of the casein micelle suspension was computed. The frequency‐dependent attenuation, α’(f ), of the spheres is taken as an unknown for this model and, by varying α’(f ), a fit between the experimental data and the predictions of the theory was obtained. This fit requires the attenuation of the micelles to vary asf1.40±0.10and the micellar attenuation to be higher than for a typical protein solution of the same concentration. This suggests that relaxation processes of the casein polypeptide chains in the casein micelles differ from those of most soluble proteins studied so far by ultrasonic attenuation measurements. This conclusion is consistent with results from nuclear magnetic resonance spectroscopy.

ISSN:0001-4966    

DOI:10.1121/1.399047

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

The acoustic radiation time signature as radiated from an infinite elastic plate is obtained for transient forced excitation applied to a point on the plate. The forced excitations considered are those encountered in industrial and marine applications such as the sudden application of dead weight, an impact load, or a sinusoidal finite length pulse that could be generated by starting machinery. The solutions in these cases were idealized by use of a point force whose time history is a step function, a square pulse, or a cw pulse. The time signature for the radiated noise was obtained by convolving the approximate acoustic radiation impulse response solution for an impulsive force with the force time history.

ISSN:0001-4966    

DOI:10.1121/1.399048

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

This paper defines the frequency domain implementation of several doublet cross detectors for broadband signals. The analytic correlator and the analytic coherence transform processes on real signals are introduced that have certain advantages as detectors over their real forms. The detectability of these cross detectors is predicted in comparison to optimal detectors.

ISSN:0001-4966    

DOI:10.1121/1.399049

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Basic principles underlying the acoustic coupling of the eardrum are illustrated in the form of a hierarchy of examples ranging from a simple piston coupled to a semi‐infinite acoustic duct, to a flexible partition coupled to a variable cross‐section duct, and to a closed cavity. The hierarchy illuminates some of the limitations of various simplified elements commonly used to model the middle ear and demonstrates the necessity of treating the acoustics and the eardrum as an integrated subsystem. Results show that the tympanic cavity and the secondary middle‐ear air chambers contribute fundamental features to the acoustic coupling of the ear. The nature of the acoustic coupling limits the passive energy absorption and transmission properties of the eardrum. The magnitude and frequency dependence of the energy dissipation within the ultrastructure of the partition, due to bending and transverse deflection, is discussed in analogy to possible dissipation mechanisms within the eardrum itself. Examples are provided for several simple systems reproducing some of the gross anatomical characteristics of the cat eardrum.

ISSN:0001-4966    

DOI:10.1121/1.399050

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Level and phase of the (2f1−f2)‐difference tone were measured as a function of primary‐tone level using the psychoacoustical method of cancellation and the objective method of emission cancellation for four frequency separations off1=1620 Hz andf2in four subjects. Differences between hearing‐ and emission‐cancellation levels ranged from 60–33 dB as Δf=f2−f1increased from 180 to 432 Hz. For smaller separations of the primaries, phase changes for emission cancellation covered a wide range and had sharp ‘‘steps,’’ whereas for hearing cancellation, the phase varied only slightly. With wider separations of the primaries, the phase became more varied for hearing cancellation and more homogeneous for emission cancellation. Both emission‐ and hearing‐cancellation level functions were nonmonotonic as a function of constant SL1and varied SL2. Remarkable phase shifts always appeared near minima in level at all separations of the primaries for emission cancellation. Four sources may be contributing to the differences in results: (a) the frequency‐dependent attenuation of the middle‐ear transfer function, (b) the frequency‐dependent mismatch of the acoustical impedances at the eardrum, (c) the frequency dependence of the microphone’s sensitivity mounted within the probe, and (d) the different reaction of active nonlinear cochlear processes on the hearing‐ and emission‐cancellation tones.

ISSN:0001-4966    

DOI:10.1121/1.399051

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Accurate cochlear frequency‐position functions based on physiological data would facilitate the interpretation of physiological and psychoacoustic data within and across species. Such functions might aid in developing cochlear models, and cochlear coordinates could provide potentially useful spectral transforms of speech and other acoustic signals. In 1961, an almost‐exponential function was developed (Greenwood, 1961b, 1974) by integrating an exponential function fitted to a subset of frequency resolution‐integration estimates (critical bandwidths). The resulting frequency‐position function was found to fit cochlear observations on human cadaver ears quite well and, with changes of constants, those on elephant, cow, guinea pig, rat, mouse, and chicken (Békésy, 1960), as well asinvivo(behavioral–anatomical) data on cats (Schucknecht, 1953). Since 1961, new mechanical and other physiological data have appeared on the human, cat, guinea pig, chinchilla, monkey, and gerbil. It is shown here that the newer extended data on human cadaver ears and from living animal preparations are quite well fit by the same basic function. The function essentially requires only empirical adjustment of a single parameter to set an upper frequency limit, while a ‘‘slope’’ parameter can be left constant if cochlear partition length is normalized to 1 or scaled if distance is specified in physical units. Constancy of slope and form in dead and living ears and across species increases the probability that the function fitting human cadaver data may apply as well to the living human ear. This prospect increases the function’s value in plotting auditory data and in modeling concerned with speech and other bioacoustic signals, since it fits the available physiological data well and, consequently (if those data are correct), remains independent of, and an appropriate means to examine, psychoacoustic data and assumptions.

ISSN:0001-4966    

DOI:10.1121/1.399052

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Flows of endolymph within the inner spiral sulcus and the subtectorial space are studied analytically. These flows are driven by boundary displacements and scala media pressure, all prescribed in the form of traveling sine waves with uniform amplitude, wave speed, and wavelength. Prescribed boundary displacements have no axial components and are assumed ‘‘small.’’ In the subtectorial space, waves are further assumed ‘‘long,’’ and inner and outer hair cells’ stereocilia are represented by permeable barriers. Boundary motions of the subtectorial space are assumed to be associated with basilar membrane motion. The localized boundary motions that would presumably accompany independent outer hair cell motions are not admitted. The pressure drop across the barrier representing the inner hair cells’ stereocilia is evaluated for four specific input conditions. The results are used to assess its relative sensitivity to three types of boundary displacement and to examine the contribution of endolymph flow to the ‘‘second filter.’’ The model predicts the introduction of appreciable tuning (102.3 dB/octave) into the auditory signal between the stages of relative normal displacement of the boundaries of the subtectorial space and the generation of a pressure drop across the inner hair cells’ stereocilia. The outer barrier is removed from the model, and the pressure drop across the inner barrier is reevaluated for the same four cases to study its sensitivity to destruction of the outer hair cells’ stereocilia. These results are examined in light of data by Robertson and Johnstone [D. Robertson and B. M. Johnstone, J. Acoust. Soc. Am.66, 466–469 (1979)].

ISSN:0001-4966    

DOI:10.1121/1.399053

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Voltage recorded from an electrode on the round window (RW) of guinea pig has characteristics that reflect the activity of auditory‐nerve fibers in the absence of acoustic stimulation. Fast Fourier transformation (FFT) of the noise recorded from the RW electrode shows a broad spectral peak from 0.8–1.0 kHz. The magnitude of the biological noise is increased by high‐frequency, bandlimited acoustic noise stimulation. Pure tones can suppress or enhance the spectral components around 0.8–1.0 kHz depending on frequency and intensity. Kainic acid applied to the intact RW membrane eliminates the biological noise (and the evoked cochlear whole‐nerve responses) without alteration of the cochlear microphonic or the summating potential. The spectral characteristics of the biological noise seem to be related to the elemental waveform contributed by the individual auditory‐nerve fibers to the voltage recorded at the RW electrode [Kiangetal.,Electrocochleography, edited by R. J. Ruben, C. Elbering, and G. Solomon (University Park, Baltimore, 1976)].

ISSN:0001-4966    

DOI:10.1121/1.399054

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

This article presents the results of two experiments investigating performance on a monaural envelope correlation discrimination task. Subjects were asked to discriminate pairs of noise bands that had identical envelopes (referred to as correlated stimuli) from pairs of noise bands that had envelopes which were independent (uncorrelated stimuli). In the first experiment, a number of stimulus parameters were varied: the center frequency of the lower frequency noise band in a pair,f1; the frequency separation between component noise bands; the duration of the stimuli; and the bandwidth of the component noise bands. For a long stimulus duration (500 ms) and a relatively wide bandwidth (100 Hz), subjects could easily discriminate correlated from uncorrelated stimuli for a wide range of frequency separations between the component noise bands. This was true both whenf1was 350 Hz, and whenf1was 2500 Hz. In each case, narrowing the bandwidth to 25 Hz, or shortening the duration to 100 ms, or both, made the task more difficult, but not impossible. In the second experiment, the level of the higher frequency noise band in a pair was varied. Performance did not decrease monotonically as the level of this band was decreased below the level of the other band, and only showed marked impairment when the level of the higher frequency band was at least 60 dB below that of the lower frequency band. The pattern of results in these two experiments is different from that which is obtained when the same stimulus parameters are varied in experiments investigating comodulation masking release (CMR). This suggests that the mechanisms underlying CMR and those underlying the discrimination of envelope correlation are not identical.

ISSN:0001-4966    

DOI:10.1121/1.399055

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

The overshoot effect was measured before, during, and after the administration of a moderate dose of aspirin. Prior to the drug, detectability of the 6‐ms, 3550‐Hz signal was 5–11 dB worse when presented 2 ms after the onset of the 200‐ms wideband masking noise than when presented 190 ms after masker onset. Following 4 days of aspirin use, detectability in the long‐delay condition was unchanged from the predrug value, but (for four of the five subjects) detectability in the short‐delay condition wasimprovedby about 4–8 dB. Thus the overshoot effect was markedly reduced by aspirin because the drug partially counteracted the normally poor detectability for signals presented soon after masker onset. This paradoxical improvement in detectability was accompanied by an aspirin‐inducedlossin detectability of 5–16 dB for a 200‐ms sample of that same signal presented in the quiet. Similar paradoxical effects have previously been obtained by inducing a temporary hearing loss with exposure to intense sound. It is presumed that the same basic mechanisms underlie the parallel outcomes. The so‐called cochlear amplifier is discussed in this regard, and also the possibility that the known differences in those primary auditory fibers having high and low spontaneous rates may be involved. A supplementary experiment demonstrated that shifting audibility with either a wideband or a narrow‐band background noise doesnotaffect the overshoot effect in the same way as does aspirin or exposure to intense sound, further suggesting that the cochlear amplifier must be altered in order for overshoot to be diminished.

ISSN:0001-4966    

DOI:10.1121/1.399056

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP