摘要:

Acute guinea pig preparations have been exposed to noise produced by a mechanical impact noise generator. Impacts were at a rate of 1/s and produced a peak sound pressure level of 130 dB at the preparation. Exposure periods of 20 min were used. Cochlear potentials in response to 6‐kHz tone bursts were recorded from differential electrodes in the basal cochlear turn. The extent of suppression and the time courses of decline and recovery associated with exposure to impact noise were measured. These results were compared with those occurring after exposure to continuous broad band white noise at an intensity such that thesame total energywas delivered to the preparation over a similar 20 min period. Tone induced responses were found to be suppressed to a greater extent by impact noise although the recovery from this exposure was more rapid. The dependence of response suppression on the rate of impacts or peak intensity has also been investigated.

ISSN:0001-4966    

DOI:10.1121/1.2003806

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

In an earlier paper [Allen, J. Acoust. Soc. Am.61, 110–119 (1977)], a linear integral equation for a two dimensional cochlear model was formulated and solved using frequency domain methods. Sondhi [J. Acoust. Soc. Am.63, 1468–1477 (1978)] then showed that the integral equation could be expressed in a symmetric form. In this talk, we show how this equation may be expressed as a circular convolution. As a result, it may be solved in the time domain, using fast Fourier transform methods, in less than 50 msec/time step. Since the solution is found in the time domain, nonlinear damping [Hall, J. Acoust. Soc. Am.61, 802–810 (1977)] may be included as a trivial extension. As a further extension, we have included logitudinal BM stiffness in the apical turn in an attempt to account for the decrease in the high‐frequency slope of neural tuning curves at lower frequencies.

ISSN:0001-4966    

DOI:10.1121/1.2003813

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Responses of auditory‐nerve fibers with high characteristic frequency (greater than 5 kHz) to characteristic frequency (CF) tones can be suppressed by tones of much lower frequency. In such cases, the fiber responses are phase‐locked to the low‐frequency suppression tone, but not to the characteristic frequency tone. Such situations are ideal for studying the temporal properties of two‐tone suppression. In this series of experiments, period histograms synchronized to the low‐frequency suppressor are computed. As the sound pressure level of a low‐frequency suppressor is increased (in the presence of a CF tone of constant level), phase‐locking to the suppressor appears at levels below those which cause a decrease in average rate. The phase of the histograms is estimated by the phase of the fundamental component of the Fourier series for the histogram. Over the range of levels where two‐tone suppression occurs, the histogram phase shifts until at high levels the phase is the same as the phase in response to the suppressor tone presented alone. That is, parts of the cycle of the suppressor tone which are excitatory at high stimulus levels can cause suppression at lower levels. [Supported by Grant No. NS12112 from NIH.]

ISSN:0001-4966    

DOI:10.1121/1.2003822

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Jayelet al.[J. Acoust. Soc. Am.63, 1093–1104 (1978)] analyzed two‐tone suppression effects when the excitatory tone (f1is higher in frequency than the suppressor tone (f2). They concluded that suppression is observable when bothf1andf2are excitatory and that its magnitude is related in part to the cochlear distance between the traveling wave maxima for the two tones. We extend these observations here to include cases wheref2f1withf2excitatory. Temporal analyses of phase‐locked discharge patterns of low‐CF neurons indicate that suppression not only exists whenf2is excitatory for bothf2f1) but also that (a) suppression magnitude may exceed 60 dB under appropriate conditions and (b) suppression magnitude declines in an orderly manner asf2is removed in frequency fromf1. For a given suppressor‐tone intensity, however, the decline of suppression magnitude with increasing frequency separation is quantitatively different forf2f1. [Work supported by a Biomedical Research Development Grant from NIH.]

ISSN:0001-4966    

DOI:10.1121/1.2003823

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

The compound Auditory‐Nerve Action Potential may be described as the convolution between the number of the eighth‐nerve fibers activated by the incoming stimulation and the single unit action potentials as seen at the gross electrode. The technique of the deconvolution may be adopted to process the measured Action Potential as a basis to retrieve information about the cochlear activity, in terms of excitation distribution along the cochlea. Since the final results are influenced by the waveshape of the unit potential adopted, this aspect will be discussed in detail. Data from human and guinea pig cochleas, in normals and in pathological ears are presented and compared. In many pathological conditions the time course of the excitation distribution were significantly altered with respect to the normative data, while the alterations seen in the Action Potential waveshapes were not easily recognized. The intrinsic limitations of this technique, i.e., the uncertainties in the determination of the unit potential, are discussed with respect to the possibility of retrieving reliable information about the activity of regions with characteristic frequencies lower than 2 kHz in the guinea pig and in man, at least for high and intermediate intensity levels.

ISSN:0001-4966    

DOI:10.1121/1.2003832

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

The make‐up of the cochlear after‐potential (PAP) and the influence of the temporal characteristics of the sound stimulus on this response were reported previously [J. Acoust. Soc. Am.63, S53 (A) (1978)]. To further illuminate the nature of this little known response input‐output and frequency response characteristics of the PAP were examined in the first and third turns of guinea pig cochleas. The cochlear microphonics, summating potentials, and (in some instances) whole‐nerve action potentials also were recorded for purposes of comparison. The peak magnitude of the PAP, specifically the positive component, tends to occur at or above the characteristic frequency of the site of recording, although the magnitude of the PAP is not sharply frequency dependent. The growth of the PAP with increasing intensity is typically much slower than the other cochlear responses. Besides contributing further to an impression of autonomy of the after‐potentials from the other cochlear responses, the results of this study demonstrate that the PAP can be elicited by a wide range of stimuli and are widely distributed in the cochlea. [Work supported by DRF.]

ISSN:0001-4966    

DOI:10.1121/1.2003838

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Topics on ADPCM and ADM technique developments in Japan are described. First, an ADPCM code sequence optimization method by K. Fushikida is discussed for an ADPCM with an adaptive quantization and fixed predictor. The method uses a technique reminiscent of dynamic programming and optimizes code sequence. It is shown that about 2‐dB SNR improvement is obtainable for speech at 32 kbps (4 bits/sample). Second, another ADPCM technique by T. Araseki and K. Ochiai is described. This technique is suitable for use at the bit rate less than 32 kbps. Two adaptive predictors connected in a cascaded form are used. One of the predictors has an ordinary small number of prediction taps. However, the other predictor possesses a considerably large number of predictor taps which are used to predict speech waveform in one pitch period apart. A backward adaptive prediction technique with a gradient method is used for each of the two adaptive predictors. Finally, performance improvement techniques and LSI implementation by A. Tomozawa and K. Niwa are described for a discretely variable slope 32 kbps ADM (DVSD).

ISSN:0001-4966    

DOI:10.1121/1.2003841

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

This paper will discuss practical implementations of speech waveform digitizers for the pre‐1980 and post‐1985 time periods. Based on requirements of expected mathematical complexity, accuracy, and redundancy of these coders, the basic hardware speeds and amount of logic to implement them will be given for today's implementations. Issues important to the commercial and military users will also be examined to ascertain how they can radically alter the architectures and hardware chosen for implementation. Then assuming that the speech digitization algorithms remain at least as complex as today's techniques, well‐known procedures for forecasting LSI improvements and cost reductions will be used in estimating the hardware needed to implement these systems in the mid‐1980's.

ISSN:0001-4966    

DOI:10.1121/1.2003845

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Speech transmission at 32 kbps by ADPCM coding offers a potential saving of a factor of 2 in bits transmitted per conversation. To evaluate the extent to which such codecs introduce perceptible degradation in the speech signal, two systems, one employing a third‐order fixed predictor, the second a third order adaptive predictor were simulated. Evaluation through relative preference tests shows a slight degradation in quality compared to Mu‐255 8 bit log PCM companding under high loading conditions (>20 dBm0) and a slight improvement in quality under low loading conditions. Comparison of our subjective preference results with a modified segmental measure of signal‐to‐noise ratio agrees with the findings of McDermottet al.[Bell Syst. Tech. J.57, 1597–1618 (1978)] for simpler codecs, namely that the segmental SNR is a significantly better predictor of the subjective quality of coded speech than the SNR measured over an entire utterance.

ISSN:0001-4966    

DOI:10.1121/1.2003854

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

The boundary value problem to be solved in computing the reflectivity of a solid, viscoelastic, ocean bottom can be formulated as a matrix differential equation with variable coefficients. In the Thomson‐Haskell techniques a solution is found by assuming the coefficients (elastic parameters) are constant over a certain depth range (a layer). If high‐velocity gradients are present a very large number of layers may be required for convergence, leading to prohibitive computer costs. A Runge‐Kutta modification of the technique yields considerable savings in computer time. The improved technique is illustrated by computation of the full reflectivity function, in frequency‐wavenumber space, of a turbidite sequence overlying basement. Synthetic pressure records obtained by two‐dimensional transformation of the reflectivity function, were analyzed as if they were field‐recorded data to attempt to recover the reflectivity. This exercise emphasizes that plane‐wave reflectivity is defined only in frequency‐wavenumber space, that any reflectivities estimated by treating energy return from the bottom as a specular reflection in the time domain must be erroneous. [Work supported by ONR.]

ISSN:0001-4966    

DOI:10.1121/1.2003857

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP