Index of content:
Volume 41, Issue 6, January 1967
- PROGRAM OF THE SEVENTY‐THIRD MEETING OF THE ACOUSTICAL SOCIETY OF AMERICA
- Session PPw. Physiological Acoustics I
- Invited Paper
41(1967); http://dx.doi.org/10.1121/1.1910538View Description Hide Description
Fishes have two sound‐sensitive organ‐systems—the lateral line, which is sensitive to the near‐field water motions of a sound source, and the swimbladder‐ear system, which is sensitive to pressure waves. Since the lateral line is spread out over the fish's body, spatially sampling the strong intensity gradient of the near‐field motions, it should be possible for a fish to localize a source of motion with this system. The swimbladder, however, is a solitary organ that samples only one point in the far field. The fish, therefore, should not be able to localize a source of pressure waves with the swimbladder‐ear system. Experimental evidence, though spotty, confirms these notions.
- Contributed Papers
Changes of Middle‐Ear Acoustic Impedance Resulting from Contralateral Noise, Female and Male Subjects41(1967); http://dx.doi.org/10.1121/1.2143548View Description Hide Description
One might hypothesize that various subjects differ in the magnitude of changes in middle‐ear acoustic impedance resulting from noise stimulation. If these impedance changes are apparently different, this may indicate differential middle‐ear musculature strength among various subjects. Twenty young adults (10 females and 10 males) with normal hearing sensitivity served as subjects for the following experiment. Measures of acoustic impedance were obtained with the Zwislocki Acoustic Bridge (Grason‐Stadler, model 3) at 500 Hz under two conditions—no noise and 105 dB SPL of white noise in the contralateral ear. As might be expected, the noise resulted in easily detectable impedance changes, however, these changes were not significantly different between the subject groups. Acoustic reactance increased for both groups (females 330 Ω and males 350 Ω), while acoustic resistance decreased for both groups (females 88 Ω and males 90 Ω). Several subjects with the smallest and greatest impedance changes were later exposed to intense noise stimulation and auditory threshold shift was measured. The results of the findings regarding impedance change and temporary threshold shift will be discussed in the paper.
Loss of Differential Pressure (SPL of Tympanic Cavity re SPL External Auditory Meatus) as a Factor in Eardrum Perforations41(1967); http://dx.doi.org/10.1121/1.2143549View Description Hide Description
This study attempts to treat the problem of sound transmission by a perforated eardrum in the general context of middle‐ear mechanics. Work with a “model” of the eardrum and bulla cavity suggested that a sizeable percentage of response loss was due to partial cancellation of directly incident pressure, as sound pressure gained access to the back of the tympanic membrane through a perforation. Wever and Lawrence (1954) and Kobrak (1959) had suggested a similar factor. The present experiments attempted to determine its magnitude. Cochlear‐microphonic (CM) responses to air‐conducted pure tones were recorded from the round window of acute cats. Sound‐pressure levels corresponding to the 10‐μV CM were measured both in the external canal and in the tympanic cavity. The following experimental conditions were systematically varied: driving system, open/closed; bulla, open/closed; eardrum, intact/perforated. From comparisons among these conditions, data were derived to represent the loss of differential pressure due to a perforation of given dimensions. [Work supported by grants from the National Institute of Neurological Diseases and Blindness, National Institutes of Health, U. S. Department of Health, Education and Welfare.]
41(1967); http://dx.doi.org/10.1121/1.2143550View Description Hide Description
Earlier experiments in animals, cadaver heads, and cochlear models gave evidence for a number of factors contributing to bone‐conduction responses [Acta Otolaryngol., Supplement No. 213 (1966)]. Based upon that evidence, a schematic impedance network of the bone‐conduction mechanism has been constructed. It indicates that there are three signal pathways: soft tissues, bone, and skull contents; and three responding components that act as independent inputs: the walls of the external canal, the ossicles, and the perilymphatic spaces. The latter are interconnected by a response line and affected by a number of modifying factors—(a) the air column in the external canal with its external opening, (b) the air bubble in the middle ear, (c) the tympanic membrane, (d) the oval and round windows, and (e) the so‐called 3rd cochlear window, the sum total of all communications between the cochlear spaces and the skull interior. [Work supported by grants from the National Institute of Neurological Diseases and Blindness, National Institutes of Health, U. S. Department of Health, Education, and Welfare.]
41(1967); http://dx.doi.org/10.1121/1.2143551View Description Hide Description
The vibrations of the human basilar membrane have been thoroughly studied by von Békésy. He used visual observation of moving silver particles on the membrane. In our preliminary experiments, we used fresh human temporal bones. The basilar membrane was exposed in the apical turn using microsurgical instruments with illumination provided by fiber optics. The cochlear fluid was moved through the round window, similar to the Békésy experiments. The movement of the basilar membrane was recorded electro‐optically, using special cochlear probes described in a paper by Jako, Hickman, and Adkins at the 72nd Meeting of the Acoustical Society. Recent developments in photosensor technology, and accurate alignment of the fiber optics with the photosensors, have permitted continuing improvements in probe resolution. This technique allows instrument recording of time, phase, and frequency relations of motions at various places along the membrane while it is stimulated by sine waves, pulses, and speech. [Supported by a grant from the American Otological Society and the volunteer efforts of the participants.]
41(1967); http://dx.doi.org/10.1121/1.2143552View Description Hide Description
The basilar papilla is one of two auditory organs found within the inner ear of most species of amphibians. It is thought to be homologous to the cochlea of higher vertebrates. We have used the techniques of light and electron microscopy to study this organ. The papilla is a short, cartilaginous, tubular extension of the saccule, terminated at the end by a thin, flat, contact membrane that separates the endolymphatic and perilymphatic spaces. Hair cells and supporting cells are arranged semicircumferentially in parallel rows along a portion of the tube. The tectorial membrane hangs from a cord that spans a diameter of the tube. From the surface of each hair cell there projects a bundle of sensory hairs, consisting of a number of stereocilia and a single kinocilium located at one side of the bundle. All hair cells are oriented in the same direction: the kinocilium is located at that side of the hair cell nearest to the contact membrane. About 350 myelinated nerve fibers innervate approximately 60 hair cells. Only one type of synapse has been found, an afferent connection between hair cells and nerve terminals. Notably absent are synapses of the sort commonly associated with efferent innervation.
41(1967); http://dx.doi.org/10.1121/1.2143553View Description Hide Description
Whitfield and Ross have proposed a nonlinear model that seems to explain summating potential that is observed in the cochlear voltage. One would not expect their model to explain the interference effect reported by Wever. However, we find that, by choosing an appropriate nonlinearity, in addition to summating potential almost all of the cochlear microphonic phenomena can be explained in terms of one nonlinear mechanism. These phenomena include distorted waveshapes observed in the cochlea; harmonic frequencies produced by distortion; combination tones, which are produced when two signals are present; and the linearization of the operating characteristic of one signal when a second signal is introduced (interference effect). A simple nonlinear analog model is discussed and the striking similarities between the behavior of the model and biological data is shown. [Work supported by National Institutes of Health, Public Health Service, U. S. Department of Health, Education and Welfare.]
41(1967); http://dx.doi.org/10.1121/1.2143554View Description Hide Description
Cochlear microphonics were recorded from round‐window electrodes in ten cats. The ears were stimulated alternately with broad‐band noise and with pure tones in the frequency range 200 to 8000 Hz. The sound‐pressure level (SPL) of the pure tone was matched in intensity to the SPL of the same frequency component within the noise, after correcting to a one‐cycle bandwidth. Results showed that the cochlear input‐output curve with noise was generally similar in shape to that produced by pure tones. However, noise was seen to suppress microphonic output at all frequencies tested. The tone‐noise response ratio was both frequency‐ and intensity‐related. Suppression of the noise response was greater with increasing stimulus intensity. Suppression was greater at frequencies above 800 Hz and was broadly related to cochlear sensitivity. Overload occurred at lower SPL's with noise stimulation than with pure‐tone stimulation. [Research supported by grants from the National Institutes of Neurological Diseases and Blindness and an anonymous donation to the Division of Otolaryngology.]
41(1967); http://dx.doi.org/10.1121/1.2143555View Description Hide Description
The scala vestibuli and/or scala tympani in guinea pigs were perfused with free Locke's solution, in which NaCl was replaced with either choline chloride or sucrose. Cochlear microphonics (CM), summating potential (SP), action potential (AP), and endocochlear potential (EP) were recorded from the basal turn before, during, and subsequent to, the perfusion. Complete replacement of the perilymph with ‐free solution did not alter EP and CM immediately, although AP was abolished rapidly. Lack of Na in the perilymph of scala tympani depressed AP more markedly than did a comparable deficiency in scala vestibuli. In most cases, the depression of AP was reversible and EP and CM showed a gradual decline after the perfusion. These data were further confirmed by the fact that tetrodotoxin at a concentration of 50λ/l did not modify EP and CM, although AP was abolished promptly. The mechanism underlying the generation of the receptor potential is discussed. [Work supported by National Institutes of Health, Public Health Service, U. S. Department of Health, Education and Welfare.]
The Longitudinal Distribution of the Cochlear Microphonic (CM) Potentials Inside the Scala Media of the Guinea Pig's Cochlea41(1967); http://dx.doi.org/10.1121/1.2143556View Description Hide Description
The cochlear microphonic (CM) potentials were recorded in each turn of the cochlea for sound stimuli between 3000 to 300 Hz, and the longitudinal distribution of the potentials were determined. For every frequency, the envelope of the CM was steeper on the side toward the base than that on the side toward the apex of the cochlea. The envelope of the CM for high frequencies had larger slopes than did the envelope for the low frequencies. This was true both on the proximal and distal sides of the maximum of the envelope. The magnitude of the slope is a linear function of the logarithm of the sound's frequency. The receptive fields of the cochlea for the sound stimuli used showed that at the level of the maximum sensitive points a given magnitude of CM (i.e., 1 mV) was obtained for all the frequencies with approximately the same sound‐pressure level (i.e., 70 dB).
41(1967); http://dx.doi.org/10.1121/1.2143557View Description Hide Description
The Mongolian gerbil is native to the region of the Gobi Desert. The gerbil cochlear and vestibular elements are unusually well exposed for study and experimental investigation. This report depicts several features of the gross and microscopic anatomy of the gerbil and describes its auditory sensitivity by the cochlear‐potential method. Criterion cochlear potentials (0.5 μV) range from 50 dB at 200 Hz to 60 dB at 30 000 Hz. In the regions of 1000 and 4000 Hz cochlear sensitivity is seen at 15 and 0 dB SPL, respectively. Comparisons are made between gerbil cochlear responses and responses from other small rodents. [Research supported by the National Institutes of Neurological Diseases and Blindness, U. S. Department of Health, Education and Welfare.]
41(1967); http://dx.doi.org/10.1121/1.2143558View Description Hide Description
Records of the summating potential (SP) obtained with high resolution from the scala tympani of the pigeon consistently show the presence of transients corresponding to both the onset and termination of a tone pulse. The ON transient is of the same polarity as the SP (negative with respect to scala media), while the OFF transient is of opposite sign and is usually greater in magnitude and duration. When the rate of onset or decay of the tone is reduced by utilizing ramp stimuli, the transients are decreased, but may not be completely abolished with rise and fall times as long as 1 sec. Stimulation of the olivocochlear bundle in the floor of the 4th ventricle sufficient to abolish the gross neural response enhances the transients as well as the sustained SP.
- Session Pw. Wave Propagation
41(1967); http://dx.doi.org/10.1121/1.2143559View Description Hide Description
The Sommerfeld‐Watson transformation is applied on the normal‐mode solution of a plane wave being scattered by an infinite, elastic, cylindrical shell immersed in a fluid and containing another fluid. The resulting residue series is generated by poles that are the complex zeroes of a six‐by‐six determinant. These zeroes are found numerically by an extension of the Newton‐Raphson method for complex functions. It is found that besides the infinity of the well‐known Franz's zeroes there exists a finite number of additional zeroes, which generate generalized Rayleigh and Stonely waves. These latter zeroes owe their existence solely to the elastic properties of the scatterer; they disappear in the limits of zero or infinite rigidity. Scattering cross sections are presented for various elastic and geometric parameters of the shell.
41(1967); http://dx.doi.org/10.1121/1.2143560View Description Hide Description
This paper extends previous work on the subject of scattering of a plane wave incident on infinite hemicylindrical bosses of a given radius with periodic spacing to those with random radii; the surface described above may be considered as one possible representation of certain surfaces encountered in practice. The probability‐density function of the radius is assumed to be uniform, and the spacing between the centers of adjacent bosses is maintained constant. The spacing is assumed to be so selected that the shadow effects are negligible for the angles of incidence considered in this study. The scalar form of Helmholtz integral formulation was used to solve this problem. Obviously, some of the inherent assumptions in this technique are invalid at the intersection of the hemicylinders and the plane background surface. This work shows that the presence of such discontinuities in the surface does not reduce the usefulness of this simple theoretical approach in calculating the scattered field in a closed form. Some numerical calculations were made using the IBM 1401 computer, and a comparison between the theoretical and experimental results for the scattered acoustic fields from various models of such surfaces supports the above results. [This work is sponsored by the Office of Naval Research.]
41(1967); http://dx.doi.org/10.1121/1.2143561View Description Hide Description
Most previous theoretical analyses were carried out with the assumption that the scattering object was either an elastic sphere, an elastic cylinder, or a rigid spheroid. Because of the importance of the penetrable spheroid problem with regard to the scattering by nonspherical bodies, as well as its relevance to the scattering by various physical objects (such as submarines, whales, etc.), the task of solving this problem is carried out. Two specific problems are considered: (a) the scattering of acoustic waves by penetrable liquid prolate spheroids; (b) the scattering of acoustic waves by penetrable elastic prolate spheroids. Numerical results using the newly compiled tables of radial prolate spheroidal functions for Problem (a) will be presented. Analytical results will be given for Problem (b). The resonance region will be emphasized. [Supported by the Office of Naval Research.]
41(1967); http://dx.doi.org/10.1121/1.2143562View Description Hide Description
The diffraction of an arbitrary acoustic pulse by an arbitrary scattering obstacle with an impedance‐boundary condition is treated by the same technique used by the author in previous diffraction studies [“Diffraction of Acoustic Pulses by Obstacles of Arbitrary Shape with a Robin Boundary Condition,” J. Acoust. Soc. Am. 41 (to be published)]. The problem is formulated as an integrodifferential equation on surface values of pressure or velocity; this equation is then solved numerically for the specific geometry of a long cylinder of square cross section struck laterally by a step pulse in pressure. A useful economy is that the coefficients used in the approximation are independent of the boundary condition and are identical to those used for previous studies involving the same geometry. Results indicate that the surface pressure decreases from the rigid‐body solution for infinite impedance to an almost constant level for the boundary impedance equal to the fluid impedance. [This work has been sponsored by the Office of Naval Research.]
Effect of Transducer Size, Shape, and Surface Sensitivity in the Measurement of Boundary‐Layer Pressures41(1967); http://dx.doi.org/10.1121/1.2143563View Description Hide Description
The measurement of a random‐pressure field by a transducer of finite size is subject to error because the transducer senses the spatial average pressure over its face rather than a point value. Methods of correction for this effect under certain conditions have been developed earlier; however, many important parameters of the system have been neglected. The present study shows the effect of various boundary‐layer parameters, as well as the shape of the transducer upon the measurement error. It is concluded that no general “true”‐size correction factor exists, but that an estimate must be made for each particular situation. The effect of nonuniform surface sensitivity of the transducer is also considered. This factor brings about an effectively smaller transducer size, but also can lead to serious errors in cross‐correlation analysis.
41(1967); http://dx.doi.org/10.1121/1.2143564View Description Hide Description
Travelling surface waves on natural bodies of water can radiate sound power into the atmosphere, although the phase velocity for surface waves is subsonic relative to the sound velocity in the atmosphere. The mathematical analysis for radiation by such waves is summarized. The analysis leads to relationships between point, line, and plane sources having travelling subsonic waves. The results for radiation from various configurations of travelling waves—e.g. circular patches, standing waves, etc.—will be presented. Those atmospheric waves whose velocity is subsonic have a “nonradiative” sound power associated with them. The results show the relationship between this latter power and the total radiated power. The corresponding analysis for surface waves having a supersonic phase velocity leads to parallel results. For surface waves travelling at exactly sonic velocity in the atmosphere, only finite wave trains are amenable to analysis.
41(1967); http://dx.doi.org/10.1121/1.2143565View Description Hide Description
On 1 April 1965, at 05:48 U.T., a meteor struck the earth in the Banff‐Penticton area of British Columbia, Canada. The meteor was sighted and recorded by seismic and infrasonic equipment. The U. S. Coast and Geodetic Survey analyzed Canadian and United States seismograms from the immediate vicinity. Sufficient acoustic, surface, and body‐wave seismic signals were recorded to outline an epicentral area of impact. This assisted the Canadian Government in carrying out an aerial photographic survey and on‐site inspection tour. This represents the most geophysical data available on this unique event, and perhaps the best documented within recent historical times.
Observations of Bond Failure Using Low‐Frequency Ultrasonic‐Pulse Attenuation and Transmission Spectra41(1967); http://dx.doi.org/10.1121/1.2143566View Description Hide Description
Burst‐continuous low‐frequency ultrasound of 66 kHz frequency was used to examine the solid‐propellant‐to‐liner bond as it undergoes failure due to constant‐load application. Specimens with failure times as long as one week were studied. Piezoelectric‐disk transducers of original design were used in a straight‐through‐transmission method. They were bolted to the sides of a circular‐sandwich specimen; the solid propellant was bonded with flexible liner to the rubber insulation on one side and to an aluminum plate on the other. Failures in each case occurred in the flexible bond. Burst‐continuous waves were sent through the specimen and the initial amplitude of the transmitted pulse was measured. The Fourier components of the transmitted pulse were obtained with an ultrasonic‐spectrum analyzer and recorded on Polaroid film. In all cases tested, as the bond was failing, there was an increase in attenuation of the transmitted pulse and a shift in the characteristic “sonic” spectrum display. The results point the way for application of “sonic” spectroscopy to materials research.