摘要:

This paper deals with the problem of estimating the parameters of the Rice distribution. The distribution has applications in sonar and radar signal processing and a proper estimation procedure with associated confidence intervals is important. Using the sample second moment as an estimate of the second moment of the distribution, two techniques, viz., methods of moments and maximum likelihood are applied to synthetic envelope data of known signal-to-noise ratios, in order to estimate the parameter from different sample sizes. It is concluded that the sample second moment is an unbiased estimate of the theoretical second moment and for the signal-to-noise ratio parameter both methods work without any significant bias and satisfy the criterion of maximum efficiency. However, the method of moments is simpler, easier to apply and therefore recommended as the method of choice.

ISSN:0001-4966    

DOI:10.1121/1.400532

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

The modeling of signal propagation or communication channels when the source-receiver or scatterer are moving at relativistic speeds is often complicated by time base distortion. In order to synthesize the received waveform, it is usually necessary to map time of signal reception to time of transmission recursively for each received time series sample. This laborious procedure which can severely limit the ability to carry out real time modeling may be considerably foreshortened if a piece-wise linear approximation is made to the motion in 3-space. Then, the recursive computation reduces to a 2-step closed-form algorithm.

ISSN:0001-4966    

DOI:10.1121/1.400533

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Many of the aspects of the interaction of spontaneous otoacoustic emissions with external tones (suppression and synchronization) can be qualitatively simulated by the behavior of a single driven Van der Pol oscillator. Analytical and numerical investigations of a model of spontaneous otoacoustic emissions based on such an oscillator (with appropriate parametric changes in the nonlinear and negative damping components) lead to predictions of the nature of the changes in suppression and synchronization (frequency-locking) tuning curves when the levels of spontaneous otoacoustic emissions are modified. Observations of the suppression and synchronization of spontaneous otoacoustic emissions by external tones of different frequencies and levels were obtained while the levels of spontaneous emissions were altered by aspirin administration. Modeling an emission as a single Van der Pol oscillator qualitatively accounts for: (1) the reduction of the level of an external tone required to suppress the emission by a decibel amount equivalent to the level reduction induced by aspirin administration; (2) the broadening of the frequency-locking tuning curve of an emission whose level is reduced; and (3) the pulling of the emission frequency by an external tone. It does not account for: (1) the observed asymmetry in the slopes of the external-tone suppression curves (more gradual for frequencies of the suppressor tone higher, rather than lower, than that of the emission); and (2) the frequency pushing of the emission by an external tone.

ISSN:0001-4966    

DOI:10.1121/1.400651

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

The first comprehensive computational modelof the precortical mammalian auditory system to include afferent neural processing up to the level of the dorsal acoustic stria (DAS) is described. The model consists of two scissile stages simulating (1) the cochlea and the auditory nerve (AN) and (2) the dorsal cochlear nucleus (DCN). The model derives its input from a 128-channel cochlear filterbank. Cochlear transduction, rectification, logarithmic compression, and two-tone suppression functions are performed at the first stage of the simulation. The 512 artificial neurons employed model the cell at the level of transmembrane potential and have interconnections that follow closely those reported in recent anatomical and physiological studies of the cat AN and DCN. The responses of the model to pure-tone stimuli (at various sound-pressure levels) and noise stimuli (at various levels and bandwidths) are reported in detail and compare well with published results. The model is being used to investigate the representation of initial English stop consonants (differing in voice-onset time) in the DAS; this work is briefly described.

ISSN:0001-4966    

DOI:10.1121/1.400652

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Measurements of the nonlinear response of the basilar membrane to a pure tone are shown to have a simple form for moderate membrane velocities:   V(x,f;Vu)/Vu≈[Ṽ(x,f)/Vu]ν(x,f), f⩽fc(x),where the responseVis the velocity of the membrane at measurement positionx,Vuis the umbo velocity,fis the frequency of the stimulus, andfc(x)is the local characteristic frequency. The frequency dependence of the functionsν(x,f)andṼ(x,f)is determined from the data, andν(x,f)andln Ṽ(x,f)are shown to be analytic functions in the lower half of the complex frequency plane, withRe{ν(x,f)}a monotonically increasing function offat fixedx. The linear limit of basilar membrane motion is characterized by a transfer functionT(x,f)=(Ṽ/V1)ν/(1−ν),estimated by extrapolatingV(x,f;Vu)/Vuto a small membrane velocityV1.T(x,f)andln T(x,f)are shown to be analytic functions in the lower half of the complex frequency plane. The inverse of the amplitude of the transfer function, which has both a deep dip atf≈fc(x)and a broad shoulder at lower frequencies, bears a striking resemblance to the neural threshold tuning curve. The functional form ofT(x,f)is used todeducethe equation governing the motion of a section of the organ of Corti. Each section acts like anegativelydamped harmonic oscillator stabilized at timetby a feedback force proportional to the velocity at the previous timet−τ.The time delay τ is proportional to the oscillator period[τ=1.75/fc(x)].Like a laser, the organ of Corti pumps energy into harmonic traveling waves. Unlike the laser, the direction of energy flow abruptly reverses as the traveling wave approaches the point of maximum membrane velocity[fc(x)≈f].All accumulated wave energy is then pumped back into a small section of the organ of Corti where transduction presumably occurs. Outer hair cells are conjectured to be active elements contributing to the negative damping and feedback of the cochlear amplifier.

ISSN:0001-4966    

DOI:10.1121/1.400653

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Threshold and suprathreshold temporal integration (TI) effects were studied in the crossed and uncrossed human acoustic stapedius reflex. Changes in reflex threshold were compared at four stimulus durations and for six threshold response criteria; suprathreshold effects were similarly compared at four stimulus durations and at five stimulus sound-pressure levels. Our results showed that reflex thresholds were significantly lower for the uncrossed condition and for longer duration stimuli. Both effects were dependent on threshold response criteria. Threshold Ti measurements in both crossed and uncrossed conditions were equivalent at low criterion levels (0%–4%,p>0.05) but were significantly larger in the crossed condition at higher criterion levels (5%–6%,p<0.05). Prominent suprathreshold effects also occurred. The main effect was characterized by significantly larger reflex magnitudes in the uncrossed condition. Duration dependent slope differences in magnitude intensity functions (MIFs) were also observed and were characterized by steeper slopes for longer duration stimuli. Saturation effects and/or intensity-dependent slope decelerations in MIFs were predominant in the uncrossed condition and for stimulus durations exceeding 20 ms. These data provide further quantitative evidence for asymmetric threshold and suprathreshold response properties of the crossed and uncrossed human acoustic stapedius reflex and demonstrate the dependence of these effects on stimuli of different durations.

ISSN:0001-4966    

DOI:10.1121/1.400534

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Basilar membrane stiffness measurements were made in the base of the gerbil cochlea. Basilar membrane stiffness was determined by contacting the basilar membrane with a stainless steel needle (tip diameter 25 μm) attached to a force transducer, putting the needle/transducer structure through a low-frequency sinusoidal excursion with amplitude 5 or 25 nm, and measuring the restoring force exerted on the needle by the basilar membrane at the applied frequency. Stiffness was calculated as the amplitude of the restoring force divided by the amplitude of the excursion. Stiffness was measured over a 24-μm range of static displacements of the basilar membrane and is presented as stiffness versus static displacement. In cochleas that were not damaged during surgery the stiffness versus displacement characteristic usually had the following features: (1) an initial stiffness plateau with average stiffness 0.6 N/m; (2) a second plateau or level off with average stiffness 9.1 N/m; and (3) an increase in stiffness beyond the second plateau that was consistent with the theoretical stiffness-vs-displacement function of a beam. These features were present both pre- and post-mortem.

ISSN:0001-4966    

DOI:10.1121/1.400535

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

When the independent spatial variable is defined appropriately, the empirical finding that the phase of the cochlear input impedance is small [Lynch et al., J. Acoust. Soc. Am.72, 108–130 (1982)] is shown to imply that the wavelength of the pressure wave in the cochlea changes slowly with position near the stapes. As a result, waves traveling in either direction through the basal turn undergo little reflection, and the transfer of energy between the middle and inner ears remains efficient at low frequencies. The slow variation of the wavelength implies that the series impedance Z̄ and shunt admittanceYof the cochlear transmission line are approximately proportional at low frequencies and thus requires that the width of the basilar membrane and the cross-sectional areas of the cochlear scalae taper in opposite directions. Maintenance of the symmetry between Z̄ andYis both necessary and sufficient to ensure that the spatial derivative of the wavelength, and hence the phase of the cochlear input impedance, remains small. Although introduced in another context, the model of Zweig [“Finding the impedance of the organ of Corti,” J. Acoust. Soc. Am.89, 1229–1254 (1991)] manifests the symmetry between Z̄ andY. In other transmission-line models of cochlear mechanics, however, that symmetry is absent, and the spatial derivative of the wavelength diverges at low frequencies—the “cochlear catastrophe.” Those models therefore contradict the impedance measurements and predict little transfer of energy between the middle and inner ears.

ISSN:0001-4966    

DOI:10.1121/1.400650

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

A number of authors [de Boer and Viergever, Hear. Res.13, 101–112 (1984); de Boer et al., inPeripheral Auditory Mechanisms(Springer-Verlag, Berlin, 1986); Hear. Res.23, 1–7 (1986); Viergever, inAuditory Frequency Selectivity(Plenum, New York, 1986), pp. 31–38; Kaernbach et al., J. Acoust. Soc. Am.81, 408–411 (1987)] have argued that backward-traveling waves, in striking contrast to waves traveling forward towards the helicotrema, suffer appreciable reflection as they move through the basal turns of the cochlea. Such reflection, if present, would have important consequences for understanding the nature and strength of otoacoustic emissions. The apparent asymmetry in reflection of cochlear waves is shown, however, to be an artifact of the boundary condition those authors impose at the stapes: conventional cochlear models are found not to generate reflections of waves traveling ineitherdirection even when the wavelength changes rapidly and the WKB approximation breaks down. Although backward-traveling waves are not reflected by the secular variation of the geometrical and mechanical characteristics of the cochlea, they are reflected when they reach the stapes. The magnitude of that boundary reflection is computed for the cat and shown to be a large, rapidly varying function of frequency.

ISSN:0001-4966    

DOI:10.1121/1.400654

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Several investigations suggest that sensitivity to changes in interaural disparities within select spectral regions may be degraded by the presence of energy at other, even remote, spectral regions. This study assessed whether similar degradations would be observed in an MLD paradigm. Detection thresholds were measured for NoSo and NoSπ. The signal, an 800-Hz tone (100-ms), was presented in continuous, broadband noise. Thresholds were also measured in the presence of a 400-Hz tone (the interferer) presented with an interaural phase disparity of 180° and gated simultaneously with the signal or presented continuously. NoSπ thresholds increased by about 7 dB with the gated interferer at 80 dB SPL. Smaller increases were observed with lower levels of the interferer. Presenting the interferer continuously reduced substantially its effect. NoSo thresholds were affected only slightly by the interferer. Reversing the roles of the signal and interferer (400-Hz signal, 800-Hz interferer) led to smaller, but reliable degradations in performance.Dioticinterferers had, in general, smaller effects on performance. The possible relation between the mechanisms that produce interference and those that foster an ability to segregate sources of sound is discussed.

ISSN:0001-4966    

DOI:10.1121/1.400655

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP