摘要:

The anatomic consequences of acoustic overstimulation are explored in this presentation, and attention is directed toward issues where improvements in technology and empirical observation are needed before further advances in our understanding can be achieved. Gains have been made in the last decade in appreciating sound‐induced cochlear injury, but there is now a need to evaluate not only cochlear pathology but also the functional state of the surviving structures. There is a wealth of information about the susceptibility of inner or outer hair cells to acoustic injury; however, the etiology of this injury is not yet fully understood. In addition, current ideas concerning the effects of noise on hair‐cell stereocilia, hair‐cell synapses, the cochlear vascular supply, and the central auditory pathways are in a state of flux and are either undergoing revision or emerging. Other issues, such as the basis of temporary or permanent threshold shift at the cellular level, and the individual differences in susceptibility to injury are in need of a fresh approach. It would seem that the time is now ripe to review our knowledge, recognize its gaps, and develop testable hypotheses concerning the mechanisms of acoustic injury to the ear.

ISSN:0001-4966    

DOI:10.1121/1.392915

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

In underwater acoustical low‐frequency applications a hydrophone with intrinsic directivity is often needed. Poled polyvinylidene fluoride (PVF2) bimorphs are suitable for design of velocity hydrophones. Because of its softness and mechanical flexibility, a PVF2 bimorph associated with an inertial structure follows water particle movement, and so the output current from the hydrophone is proportional to the particle velocity of the incident wave. Moreover, the PVF2 bimorphs manufactured in our laboratories (whose thickness may be greater than 1 mm), make possible a compromise between the opposite requirements that a high sensitivity demands a thick polymer and for a high mechanical flexibility of the membrane (to obtain the lowest possible resonance frequency) a thin bimorph is needed. The study of a low‐frequency particle velocity calibration system made possible the achievement of small lightweight PVF2 velocity hydrophones showing an intrinsic directivity below 100 Hz. The same hydrophone can be connected so as to be also pressure sensitive: Intensity measurements might become possible with only one sensor.

ISSN:0001-4966    

DOI:10.1121/1.392916

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

An acoustic levitation technique has been used to measure acoustical properties of single drops of a number of pure oils, some of which are found in the porpoise dome. Some of the data may be useful in elucidating the relation between lipid composition and sound transmission in porpoise head.

ISSN:0001-4966    

DOI:10.1121/1.392917

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

UltrasonicB‐mode images are formed from echoes backscattered from tissue structures in the body. Quantitative analysis of this signal from tissues may provide additional information about the tissues which may be valuable for clinical diagnosis. Results on measurements of backscatter properties of tissues such as heart, liver, and blood have been reported by a number of investigators. Data on other tissues such as spleen, kidney, and pancreas, however, are still very scanty. In this paper, results on ultrasonic backscattering properties of bovine heart, liver, kidney, spleen, pancreas, and rat myocardium, recently obtained in our laboratory utilizing a computerized system over the frequency range of 2–7 MHz, are presented. The results show that for all the tissues investigated, backscatter from liver is the highest, while that from spleen is the lowest. Liver and pancreas exhibit frequency dependence distinctively different from other tissues. Moreover, backscatter from bovine myocardium is found to be higher than that from rat myocardium. The significance of these findings in relation to the histological composition of these tissues is discussed.

ISSN:0001-4966    

DOI:10.1121/1.393115

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

Three experiments were conducted to study the effect of segmental and suprasegmental corrections on the intelligibility and judged quality of deaf speech. By means of digital signal processing techniques, including LPC analysis, transformations of separate speech sounds, temporal structure, and intonation were carried out on 30 Dutch sentences spoken by ten deaf children. The transformed sentences were tested for intelligibility and acceptability by presenting them to inexperienced listeners. In experiment 1, LPC based reflection coefficients describing segmental characteristics of deaf speakers were replaced by those of hearing speakers. A complete segmental correction caused a dramatic increase in intelligibility from 24% to 72%, which, for a major part, was due to correction of vowels. Experiment 2 revealed that correction of temporal structure and intonation caused only a small improvement from 24% to about 34%. Combination of segmental and suprasegmental corrections yielded almost perfectly understandable sentences, due to a more than additive effect of the two corrections. Quality judgments, collected in experiment 3, were in close agreement with the intelligibility measures. The results show that, in order for these speakers to become more intelligible, improving their articulation is more important than improving their production of temporal structure and intonation.

ISSN:0001-4966    

DOI:10.1121/1.392918

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

The study was designed to test the validity of the American Academy of Ophthalmology and Otolaryngology’s (AAOO) 26‐dB average hearing threshold level at 500, 1000, and 2000 Hz as a predictor of hearing handicap. To investigate this criterion the performance of a normal‐hearing group was compared with that of two groups, categorized according to the AAOO [Trans. Am. Acad. Ophthal. Otolaryng.63, 236–238 (1959)] guidelines as having no handicap. The latter groups, however, had significant hearing losses in the frequencies above 2000 Hz. Mean hearing threshold levels for 3000, 4000, and 6000 Hz were 54 dB for group II and 63 dB for group III. Two kinds of speech stimuli were presented at an A‐weighted sound level of 60 dB in quiet and in three different levels of noise. The resulting speech recognition scores were significantly lower for the hearing‐impaired groups than for the normal‐hearing group on both kinds of speech materials and in all three noise conditions. Mean scores for group III were significantly lower than those of the normal‐hearing group, even in the quiet condition. Speech recognition scores showed significantly better correlation with hearing levels for frequency combinations including frequencies above 2000 Hz than for the 500‐, 1000‐, and 2000‐Hz combination. On the basis of these results the author recommends that the 26‐dB fence should be somewhat lower, and that frequencies above 2000 Hz should be included in any scheme for evaluating hearing handicap.

ISSN:0001-4966    

DOI:10.1121/1.392919

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

Signal detection in diotic (NoSo) and dichotic (NoSπ) conditions was measured as a function of the stimulus parameters of the noise that preceded the signal‐plus‐masker. When the signal and masker were both pulsed, dichotic signal detection was worse than when the masker was continuous or when the onset of the masker preceded the signal‐plus‐masker by at least 500 ms. The dichotic detection thresholds decreased as the duration of the pulsed signal plus pulsed masker was increased. The level, spectrum, interaural configuration, duration, and temporal proximity of the prior noise (forward fringe) relative to the masker and/or signal and masker were all investigated. Almost any difference between the parameters of the fringe and the masker resulted in poorer signal detection in the dichotic conditions. These same stimulus conditions produced small (less than 2.2 dB) changes in the diotic detection thresholds. The various models of the Masking‐Level Difference (MLD) may be modified to qualitatively describe some of these results.

ISSN:0001-4966    

DOI:10.1121/1.392920

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

A series of experiments was performed to examine the extent to which precision of interaural time discrimination depends on the sound‐pressure level (SPL) and/or sensation level (SL) of the signal. All experiments used a tone burst signal and a continuous white noise masker, which was either diotic or interaurally phase reversed. Results of the first experiment indicate that (1) at equal signal SLs, interaural time and intensity discrimination is more precise when measured with the added diotic noise, and (2) addition of the phase reversed noise, previously shown to cause less precise interaural time discrimination, has a similar effect on interaural intensity discrimination. In the second experiment, interaural time JNDs for a signal of constant SPL were measured as a function of noise level. Results show that a low‐level diotic noise can benefit interaural time discrimination, particularly at 500 Hz. The third and fourth experiments were performed to measure interaural time discrimination as a function of increasing signal SPL but constant signal‐to‐noise ratio. The data show the JND decreasing with increasing signal SPL at nearly the same rate with or without the added noise, indicating that an increase in signal‐to‐noise ratio is not necessary for improved discrimination.

ISSN:0001-4966    

DOI:10.1121/1.392921

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

The motion of the amphibian eardrum under free‐field acoustic stimulation was investigated using time‐averaged holography. We show that the amplitude is linearly related to sound pressure up to ±1000 nm. The frequency response of the eardrum shows broad resonance characteristics with a main peak between 1200–2200 Hz. The velocity of the tympanic membrane’s motion at its resonance frequency matches the acoustic velocity of air particles. The resonance characteristics of the eardrum are also revealed by white noise stimulation. The power spectrum obtained by Fourier transformation of the autocorrelation of the response to noise resembles closely that obtained by holography.

ISSN:0001-4966    

DOI:10.1121/1.392922

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

Behavioral and acoustic reflex thresholds were determined for five normal‐hearing subjects in response to carrier signals of 500 and 2000 Hz which were unmodulated or modulated sinusoidally at rates of 2, 20, and 200 times per second with frequency deviations (Δ f) of 30, 100, and 300 Hz. Behavioral (absolute and masked) thresholds were determined using an adaptive two‐alternative forced‐choice procedure. Acoustic reflex thresholds were determined by visual inspection of stored reflex waveforms. Frequency modulation was not found to exert a systematic effect at absolute threshold. Frequency modulation did affect threshold estimates systematically, but differentially, at masked threshold and acoustic reflex threshold. Increasing the frequency deviation of the modulation was associated with an increase in masked threshold and with a decrease in acoustic reflex threshold at both test frequencies. The findings are discussed in terms of critical band phenomena.

ISSN:0001-4966    

DOI:10.1121/1.392923

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP