摘要:

Measurements of group delay were made extracellularly from spiral ganglion cells in the 3.7 to 5.0‐mm region of the guinea pig cochlea, using sinusoidally amplitude modulated tones with constant modulating frequency (100 Hz) and depth of modulation (0.19). Threshold cochlear tuning was accompanied by frequency‐dependent group delays. The group delay on the low‐frequency tail was independent of carrier frequency; the interunit variation was 0.28–1.28 ms. The difference in group delay between CF and the low‐frequency tail decreased as the CF threshold increased (−0.09±0.02 ms per 10 dB, beginning at 0.62±0.07 ms at 0 dB SPL). The group delay decreased above CF; at the units’ maximum frequency it was less than the low‐frequency tail value, and was sometimes negative. Following arterial injections of furosemide the CF threshold increased and the group delay peak decreased; the low‐frequency tail was unaffected. The group delay decreased with increasing intensity; the reduction near and above CF was not only larger than that on the low‐frequency tail, but also the change at 5–10 dB above threshold was far greater than expected from theQ10 dBof the suprathreshold iso‐rate tuning curves. A minimum‐phase analysis suggested that the group delay response above CF, together with its nonlinear behavior, can be accounted for by a high‐frequency, level‐independent, amplitude plateau, in combination with the single unit, amplitude nonlinearity which is known to exist above CF.

ISSN:0001-4966    

DOI:10.1121/1.391456

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Recent psychoacoustic experiments have shown that interaural time differences provide adequate cues for lateralizing high‐frequency sounds, provided the stimuli are complex and not pure tones. We present here physiological evidence in support of these findings. Neurons of high best frequency in the cat inferior colliculus respond to interaural phase differences of amplitude modulated waveforms, and this response depends upon preservation of phase information of the modulating signal. Interaural phase differences were introduced in two ways: by interaural delays of the entire waveform and by binaural beats in which there was an interaural frequency difference in the modulating waveform. Results obtained with these two methods are similar. Our results show that high‐frequency cells can respond to interaural time differences of amplitude modulated signals and that they do so by a sensitivity to interaural phase differences of the modulating waveform.

ISSN:0001-4966    

DOI:10.1121/1.391457

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Short‐latency auditory responses were derived by cross correlation of pseudorandom white noise with averaged scalp potentials in guinea pigs. The cross‐correlation functions were characterized by distinct cochlear microphonic and neural components, as distinguished by susceptibility to hypothermia and masking noise. This technique detects only linear, frequency‐following responses of the auditory system, and demonstrated neural frequency following up to 3–4 kHz; thresholds were about 30–40 dB spectrum level. While conventional auditory brain stem responses reflect onset neural activity and are most responsive to high‐frequency stimuli, cross‐correlation responses reflect frequency‐following activity, primarily to low frequencies, and thus may represent a complementary method of electrophysiologic assessment of the auditory system. Data are very rapidly acquired, and estimation of responses of limited areas of the cochlea may be possible by off‐line digital filtering of cross‐correlation functions obtained with broadband noise stimuli.

ISSN:0001-4966    

DOI:10.1121/1.391458

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

A stochastic (random) process may be nonstationary if its stochastic features vary with a shift of time. For the most practical processes, although more or less nonstationary, the generalized harmonics representation still makes sense; so does the spectral density function which is now defined as being ‘‘evolutionary’’ in view of the time dependency. The present paper briefly reviews this spectral description for a nonstationary process and further models it as the output from a white‐noise excited time‐variant shaping filter. With this model the nonstationary processesX(t) andY(t) are denoted as ∫∞−∞Ax,t(ω)ejωt dW(ω) and ∫∞−∞Ay,t(ω)ejωt dW(ω), respectively, whereAx,t(ω) andAy,t(ω) are the so‐called modulation functions (MFs) anddW(ω) is a random variable which retains the orthogonality. Previous papers have investigated and shown some advantage of using such a modulation function (MF) description in solving many practical nonstationary problems which hinged on the concept of the evolutionary auto/cross‐spectral density (EASD/ECSD). In this paper an attempt is made to apply further this MF model to describe the time‐varying auto/cross‐covariance functions (ACVF/CCVF) for the nonstationary processes and it is found that they are closely related to the relevant MFs butnotto the EASD/ECSD in the Fourier transform sense, as has been summarized in the well‐known Wiener–Khintchine (W–K) relationship for the stationary processes. The new relationship has effectively generalized the W–K theorem in a special way, which has been proven efficient and accurate to both the synthetic signals such as the uniformly amplitude‐modulated process, the uniformly frequency‐modulated process and random‐phase process, and to the practical signals such as the nonstationary acoustic processes.

ISSN:0001-4966    

DOI:10.1121/1.391625

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

A tomographic method flow distribution estimation from the data of time of flight of pulsed sound waves among fixed stations is examined for the case of plane flow detection in a water tank. The errors due to the limited number of stations and the effects of the use of a pseudoinverse method are examined under practical conditions. Experimental results showed the usefulness of the method in these cases.

ISSN:0001-4966    

DOI:10.1121/1.391459

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The phase trend in multi‐degree‐of‐freedom systems can be determined by an algorithm that tracks the relative signs of adjacent resonances in a modal expansion of transfer functions. This algorithm is expressed in analytical form for two‐dimensional systems. The analytical expression shows the transition from input function phase to the reverberant phase limit. The phase trend for two‐dimensional systems greatly exceeds that of the average response of such systems and the reason for this difference is analyzed.

ISSN:0001-4966    

DOI:10.1121/1.391426

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The analysis of Rayleigh wave propagation in crystals is carried out in the cases for which, on the one hand, Christoffel equations split into two parts providing a Rayleigh wave polarized in the sagittal plane, and on the other hand, boundary conditions simplify under the conditions that some elastic constants vanish. It is shown that these requirements are satisfied by 16 configurations in crystals belonging to the orthorhombic, tetragonal, cubic, and hexagonal symmetry systems. The three particular cases solved by Stoneley [R. Stoneley, Proc. R. Soc. London, Ser. A232, 447–458 (1955)] are included. The equations giving the velocity and the mechanical displacement are established. The influence of the anisotropy factor on the decay constant is emphasized for crystals belonging to the cubic or tetragonal systems. Curves showing the decrease of the longitudinal and transverse components of the mechanical displacement are given for YAG, Si, GaAs, TiO2, and TeO2. Oscillations and a very slow decrease versus depth of the mechanical displacement components were observed for TeO2. These are ascribed to the strong anisotropy of this crystal.

ISSN:0001-4966    

DOI:10.1121/1.391427

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Effects of random bottom structure on acoustic intensity in isospeed shallow water are studied. The randomness is due to stochastic variations in the bottom density and sound speed in the horizontal direction beneath a plane water–bottom interface. Ray geometry, spreading loss, and bottom loss and phase shift are examined in order to derive formulas for mean intensity and the variance of intensity. The expressions obtained are sufficiently general to permit their use with different bottom‐acoustic models of sound reflection. In this paper, for illustrative and comparative purposes, two such models, one developed by Mackenzie and the other by Rayleigh, are considered. The distinctive acoustic consequences of bottoms of different density mean, variance, and horizontal correlation are discussed, as are comparisons of results for the two bottom‐reflection models. Intensity moments are obtained also for differing source–receiver range and water depth.

ISSN:0001-4966    

DOI:10.1121/1.391428

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

A Green’s function extension of image theory allows the sound field in an absorbing fluid substrate underlying a fluid wedge of slower sound speed to be evaluated on a desktop computer. (1) Solutions based on an end‐point approximation, valid at great distances from the apex of the wedge and for absorptions representative of sedimentarylike materials, show a beam peaking at a depth close to that predicted by more complicated models. An additional random‐phase assumption provides a functional dependence for this angle identical with that obtained by a more elaborate procedure. (2) Solutions based on a saddle‐point approximation are valid below the apex and for arbitrary absorption. At moderate absorption, these solutions are consistent with those observed in the farfield. For small absorption, the sound field displays a heretofore unnoticed structure that is consistent with the mutual interference of sound beams entering the substrate at various distances from the apex. Some previously unreported measurements of the sound field in the substrate support the predictions of the saddle‐point approximation.

ISSN:0001-4966    

DOI:10.1121/1.391429

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Probability distributions of intensity fluctuations from the MATE, AFAR, and S. W. Bermuda underwater acoustics experiments are compared with recently derived theoretical expressions. The limitations and strengths of these expressions are discussed. In particular, it is found that the work of Furutsu [J. Math. Phys.17, 1252–1263 (1976)] gives a good description of the probability distribution function of intensity or log intensity, requiring only a knowledge of the second‐ and third‐order intensity moments. Furutsu’s description is not asymptotically correct at large range, so a modified form is proposed for the moments of intensity that reduce analytically to the log‐normal distribution at short range and to the exponential distribution at large range. This new form also predicts the higher moments well but cannot be inverted analytically. A numerical inversion is used, and the ensuing distribution agrees well with the analytical result of Furutsu. It is expected that the new expression will be applicable at all ranges.

ISSN:0001-4966    

DOI:10.1121/1.391430

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP