摘要:

Impaired‐ and normal‐hearing subjects (Ss) identified the pitch of either a low‐, mid‐, or high‐frequency noise burst in a recognition‐masking task with a two‐formant vowel masker which preceded and/or followed the noise burst.F1 of the vowel was at 700 Hz andF2 at 1100 Hz. The three noise bursts were bands of flat‐spectrum noise: 500–1500 Hz, 1500–4000 Hz, or 4000–6000 Hz. Forward‐, backward‐, and combined‐forward‐and‐backward‐masking conditions were tested with a 10 ms Δt. The vowel was presented at most comfortable listening level (MCL) for the impaired and at 90 dB SPL for the normal‐hearing Ss: the noise bursts were presented at 10 dB SL. Pitch recognition of the noise bursts was affected least in the backward‐masking condition and was poorest in the combined‐forward‐and‐backward‐masking condition. In the combined masking condition nearly all Ss showed some masking of pitch recognition for one or more of the noise bursts. Masking occurred most often for the low‐frequency burst and least often for the high‐frequency burst. Generally, release from masking was seen when Δtwas lengthened to 100 ms.

ISSN:0001-4966    

DOI:10.1121/1.2017076

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Patients with clinically diagnosed hearing losses were given the verbal tests and threshold measurements used in the USPHS Health and Nutrition Examination Survey for 1971–75. A computer program for categorizing hearing losses from recognition data [J. Acoust. Soc. Am.61, S5(A) (1977)] was applied to the results of the tests. permitting comparison between results of the ordinary clinical tests and computer‐aided diagnoses. The program estimates mixtures of losses whereas clinical tests other than hearing by bone conduction primarily diagnose the major component. For minor hearing losses, the speech test does not resolve unequivocal differences between conductive and sensorineural losses, but for higher threshold elevations it appears to resolve conductive, sensorineural, and recruiting components.

ISSN:0001-4966    

DOI:10.1121/1.2017077

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Vowel intelligibility is important in communication through lipreading. We studied articulation as one source of vowel confusion. An adult female was filmed frontally at 18 fps as she spoke a random list of ten vowels (/i, ɪ, ɛ, æ, a, ɔ, ᴜ, ᴜ, ʌ, ɝ/) and six diphthongs (/aɪ, eɪ, ɔɪ, aᴜ, oᴜ, jᴜ/) in /b/‐V‐/b/ context (five tokens each). This silent film was shown to twenty normally hearing adults for visual vowel identification. Confusion matrices indicated distinction between rounded (back) vowels, spread (front) vowels, and most diphthongs. High intelligibilities for /i, a, ɔɪ, aᴜ, oᴜ, jᴜ/ and low intelligibilities for /ɪ, ɛ, æ, ɝ/ were obtained, as in several previous studies. Not all tokens of a given vowel were equally intelligible. To examine the relation between articulation and vowel intelligibility, the film images were studied frame‐by‐frame. Measurements were made of frontal articulatory parameters presumed to be important for visual identification of vowels (vertical and horizontal mouth opening, lip thicknesses, teeth visibility, and jaw displacement). Data suggest that highly intelligible tokens are characterized by extreme articulatory changes and quasi steady‐state segments. Tokens which evoke similar response distributions (regardless of intended vowel) exhibited similar patterns of articulatory change. The results suggest articulatory rules for optimizing communication of vowels through lipreading. [Work supported by NINCDS grant NS03856.]

ISSN:0001-4966    

DOI:10.1121/1.2017086

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Continuous discourse material with a background of interfering (“Cafeteria”) noise was processed by eight different hearing aids fitted to KEMAR. Tape recordings of the processed signals were then presented in pairs to individual listeners, whose judgements of relative intelligibility were used to eliminate competing aids and select an eventual winner. Discrimination scores were also obtained from each listener, using speech discrimination tests processed under identical conditions. In general, for each individual, there was a high correlation between the aid selected by paired comparisons and that selected by the highest discrimination score. Thus paired comparisons appeared to be a reliable means of identifying hearing aids yielding maximal speech discrimination scores. However, some aspects of the results raised questions about the nature of intelligibility judgments and whether different types of test material or different characteristics of the background noise might lead to different hearing aid selections. The problem of selecting valid testing procedures will be discussed. [Work supported by NIH.]

ISSN:0001-4966    

DOI:10.1121/1.2017092

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

The calibration of a standard audiometric headset is dependent upon headband tension. Similarly the attenuation provided by this standard, supra‐aural headset is dependent upon the headband tension, and headband tension may change observably during clinical use. This is especially pertinent when one considers that masking from background noise is a serious problem when hearing levels are measured at or near the low reference threshold levels specified in the American National Standards Specifications for Audiometers, ANSI S3.6‐1969. In the present study the degree of headband tension change during clinical threshold audiometry has been measured empirically. In addition the effect of these tension changes upon the obtained pure‐tone thresholds at several frequencies were determined. Significant differences in obtained thresholds contingent upon deterioration of headband tension were noted. Results of this experiment will be discussed by reference to modeling of the acoustic impedance characteristics of a simple, single‐cavity audiometric headset.

ISSN:0001-4966    

DOI:10.1121/1.2017098

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

A new method to enhance the low‐frequency sound attenuation characteristics of a lined duct is presented. A rigid, longitudinal splitter plate is used to separate the lined duct section into two parallel branch ducts. The phase speed of the fundamental sound mode in each parallel branch is a function of the liner configuration and can differ substantially from the free space phase speed. By lining the parallel branches dissimilarly, destructive interference of the fundamental mode of the transmitted wave occurs downstream of the parallel absorbers at a selected set of frequencies. Strong reflections also occur at the silencer inlet for a larger set of frequencies due to an acoustical impedance mismatch at the junction of the main duct and the parallel branches. These interference effects, which result from placing the rigid splitter plate into the lined duct can increase the low‐frequency transmission loss of the duct by more than two fold over a broad low‐frequency band and by as much as 5‐dB/unit duct width at selected frequencies.

ISSN:0001-4966    

DOI:10.1121/1.2017101

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

The justification for, or arguments against, noise control is often based on the economic costs of abatement, the dollar costs of incurred illnesses or compensation to workers, or the dollar degradation of property caused by industrial or community noise. But there are other costs that are difficult to quantify in any terms, much less in dollar amounts. This paper provides a brief discussion of the problems of trying to quantify concepts that essentially cannot be quantified.

ISSN:0001-4966    

DOI:10.1121/1.2017112

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Whole nerve compound action potentials (APs) are used to determine AP threshold curves of individual chinchillas. Initially, each animal is implanted with a chronic round window electrode that is connected to a small plug fastened to the skull. After recovery from surgery the animal is suspended in an anechoic chamber and presented with free‐field tone‐bursts. Computer‐averaged APs (N= 128), monitored on an oscilloscope, are used for visual detection ofN1, thresholds for several tone‐burst frequencies from 0.5 to 20 kHz. In this manner, a threshold curve is determined on the basis of data accumulated over at least four separate days. Animals considered to have normal thresholds are then placed on a kanamycin regimen. Kanamycin, an ototoxic antibiotic, produces a lesion that progresses through the cochlea from base to apex, preferentially destroying outer hair cells; hence, the first effects of the drug are manifest as a threshold shift at higher frequencies. Animals receiving kanamycin injections are monitored daily in the same manner that established their initial threshold curves. The extent of cochlear damage is reflected in postkanamycin threshold curves. [Work supported by NINCDS.]

ISSN:0001-4966    

DOI:10.1121/1.2017117

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

A new method of ultrasonic frequency analysis is introduced which employs frequency tracked gated rf drive pulses rather than shock‐excited broadband spikes for the ultrasonic waveform. The new technique, a variation of the sampled‐continuous wave technique, eliminates problems associated with finite pulse widths and transducer ring‐down of conventional methods. It is shown to yield correct ultrasonic wave velocity measurements of the sample irrespective of receiver gate width or position provided any portions of two successive echoes are gated simultaneous into the spectrum analyzer. The experimental observations are substantiated by a theoretical model based on the time‐frequency domain formulation of ultrasonic frequency analysis.

ISSN:0001-4966    

DOI:10.1121/1.2017120

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP