摘要:

The neighborhood activation model (NAM) of auditory word recognition describes the processes by which a stimulus word is identified in the context of phonetically similar words activated in memory. Stimulus input activates a set of acoustic‐phonetic patterns in memory that must be discriminated and chosen among. These acoustic‐phonetic patterns receive activation levels proportional to their similarities to the stimulus input. The activation levels may then be adjusted by biases arising from higher‐level information, such as word frequency. The interaction of the bottom‐up sensory input and top‐down biasing information is assumed to take place within individual processing units called word decision units. These units monitor the activation levels of their acoustic‐phonetic patterns, any higher‐level information that may optimize decisions among the competing patterns, and the activity of all other word decision units. The NAM states that increasing the number of acoustic‐phonetic patterns activated in memory by the stimulus input will slow processing and reduce identification accuracy. It also states that effects of word frequency are directly tied to the number and nature of similar words activated in memory and that word frequency is not intrinsic to the activation levels of the acoustic‐phonetic patterns. [Work supported by NIH Grant NS‐12179.]

ISSN:0001-4966    

DOI:10.1121/1.2024135

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

The effects of different types of linguistic context on the intelligibility of spoken language were examined. A set of words was produced by the same speakers in three different types of linguistic context: ordinary sentences, anomalous sentences, and a word list context. The anomalous sentences were constructed by changing one nonadjacent‐to‐target word to an anomalous alternative. The word list context was set up as short, sentencelike strings, seven words in length, including the target word. In the production phase of the experiment, speakers were instructed to speak with the same intonation over all the materials. To encourage this, the different context types were randomly interleaved in the materials which speakers read. No significant differences were found in the intelligibility of the words produced in the different context conditions. It is argued that these results demonstrate that, contrary to the findings of (Lieberman, 1963), it is the overall speech “mode,” rather than the immediate linguistic context, which acts to determine the intelligibility with which individual words are produced.

ISSN:0001-4966    

DOI:10.1121/1.2024182

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

When discriminating pairs of stimuli from an acoustic voice‐onset‐time (VOT) continuum, English‐speaking listeners typically show a performance peak in the region of the phonetic category boundary. An ongoing series of experiments demonstrates that the location and height of this peak are affected by preceding phonetic context. While any preceding context appears to lower discrimination performance, perhaps by interfering with auditory memory, a preceding [s] also shifts the peak towards the short‐VOT end of the continuum and, correspondingly, increases “voiceless” responses in a labeling task. This latter effect (trivial within a syllable because of English spelling conventions) occurs even when a word boundary intervenes and does not seem to be mediated by the duration of the silent closure interval following the [s]. A hypothesis currently being pursued is that phonological voicing decisions for word‐initial stop consonants are sensitive to the voicing status of preceding phonetic segments. [Work supported by NICHD.]

ISSN:0001-4966    

DOI:10.1121/1.2024226

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

In the present study, the perceptual performance of 24 English monolinguals and 24 German‐dominant German‐English bilinguals was subjected to detailed analysis. Stimuli consisted of 57 semantically anomalous natural and vocoded English sentences. Results revealed that the monolinguals made an average of 5.92 errors and the bilinguals 66.58 errors in the natural condition, while the monolinguals made an average of 30.58 errors and the bilinguals 83.17 errors in the vocoded condition. For both groups, phonemic errors predominated, although approximately 30%–40% of the errors were morphosyntactic and/or lexicosemantic. {These latter results were essentially in agreement with previous findings [M. Mack and B. Gold, MIT Lincoln Laboratory Tech. Rep. 703 (1985) and J. Acoust. Soc. Am. Suppl. I77, S10–S11 0985)].} Further, the bilinguals' responses to the vocoded stimuli suggested that they were employing a theory‐driven rather than a data‐driven response strategy, presumably due to the difficulty of the task. [Work sponsored by the Department of the Air Force.]

ISSN:0001-4966    

DOI:10.1121/1.2024270

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Tests of the noise excluding properties of the TDH,50P/MX‐41AR, the Audiocup, and the ER‐3A insert earphone were performed in a diffuse‐field facility complying with ANSI S12.6‐1984. Data on attenuation were obtained monaurally with the nontest ear plugged and muffed. Results generally agreed well with previously reported measurements. A broadband noise, shaped by a multifilter, allowed a direct test of the ANSI S3.1‐1977 permissible background noise levels for testing to audiometric zero under TDH‐39/MX‐41AR headphones. This “ANSI noise” raised the average thresholds of 15 normal‐hearing test subjects by 3 to 5 dB at the 500‐ to 4000‐Hz octave frequencies. With a noise shaped to the less stringent OSHA‐1983 regulation, average thresholds were raised 9 to 17 dB. Introduction of an “ENT office noise” with 55 dB(A) overall level raised average thresholds at those frequencies by 11, 5, 1, and 0 dB with the Audiocups and less than 2 dB with the recommended fully (“deeply”) inserted ER‐3A eartips. Measured threshold elevations agreed closely with predictions based on a critical ratio calculation utilizing actual sound field noise levels and measured attenuations. A conservative rule of thumb for testing to audiometric zero with the ER‐3A earphone appears to be an office noise level of 45 dB(A) or less.

ISSN:0001-4966    

DOI:10.1121/1.2024312

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Military vehicles are designed for maximum capabilities in areas of performance, armament, and endurance. Acoustic noise suppression at the source is not considered in the system design because of its degradation on performance, as well as its cost impact. Therefore, it is left to the crew helmet to provide for the hearing protection of the crew member. In order to protect the hearing and improve the job performance of the crew, there are two major noise paths to be considered: first is the noise pickup by the communication microphone, along with the speech communication; second is the environmental noise that penetrates the earcup. It is believed that additional improvements to such devices as noise canceling microphones and earcup/transducer assemblies have reached their practical limits. Therefore, research efforts are presently being conducted to incorporate active speech processing for rejecting noise picked up by the communication microphone, and active noise reduction to reduce the environmental noise penetrating the earcup. These efforts will be discussed, along with new types of test equipment and evaluation procedures that have been developed to more accurately evaluate existing communication components and future active speech processing/noise reduction systems.

ISSN:0001-4966    

DOI:10.1121/1.2024367

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

The final results of an experimental investigation to study the extent of frequency regionalization in the ear of goldfish are presented. Goldfish about 6 in. in body length were subjected to intense tones at 250 and 500 Hz, and four different sound‐pressure levels. They were placed in a waveguide and constrained as close as possible to a pressure antinode so that the primary response of the inner ear was due to the induced motion of the swimbladder and Weberian ossicles. Both saccular and lagenar maculae were examined under a scanning electron microscope to determine the location and extent of hair cell damage as a function of frequency and sound‐pressure level. The results are not inconsistent with the gross frequency regionalization in the saccular macula of codfish determined by P. S. Enger [Hearing and Sound Communication in Fishes(Springer, New York, 1981), pp. 243–255]. In addition, the results indicate a possible breakdown of the Weberian apparatus at extremely high sound‐pressure levels where the primary site of damage switches from the saccule to lagena. This is consistent with the behavior of the system based on its viscoelastic properties as postulated by R. McN. Alexander [J. Exp. Biol.38, 747–757 (1961)]. Work supported in part by ONR and NIH.]

ISSN:0001-4966    

DOI:10.1121/1.2024415

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Measurement of electrophysiological thresholds for specific frequencies in animals has been limited due to spectral problems when using brief broadband pulse stimuli necessary to elicit synchronous neural discharge. Frequency specific stimuli usually fail to yield responses any closer than 10–20 dB to actual behavioral thresholds. When a compound action potential obtained from a pulse or tone‐burst stimulus is subtracted from a potential obtained with the original stiumuls plus a low‐intensity continuous pure‐tone masker, estimates of thresholds are near behavioral thresholds than measurements obtained using short duration stimuli alone. The effects of presentation rate (27.7 to 77.7/s), number of sweeps (625 to 10 000), and level of the continuous tone stimulus (−10 to 50 dB SPL) in a series of guinea pigs have been examined. Optimal recording conditions yielded thresholds to sine waves that are within 5 dB of behavioral data presented by Heffneret al.[J. Acoust. Soc. Am.49, 1888–1895 (1971)], and somewhat less sensitive than data presented by Prosenet al.[J. Acoust. Soc. Am.63, 559–566 (1978)]. [Work supported by DRF.]

ISSN:0001-4966    

DOI:10.1121/1.2024463

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

The Gaussian beam method (GBM) has found wide application in seismology for charting high‐frequency wave propagation through heterogeneous environments. Unlike ray fields, Gaussian beams negotiate convergence zones without requiring caustic corrections. Because of these attributes, GBM may be useful also for sound field propagation in a realistically range‐ and depth‐dependent ocean. However, in its conventional and facile implementation via a discretized stack of paraxially approximated beams, GBM is not a discipline witha prioripredictive capability. By comparison with various canonical test problems, the accuracy of GBM has been found to depend strongly on the choice of arbitrarily assignable beam and stacking parameters. Here, the method is tested on previously not investigated multiply reflected fields in a range‐independent duct bounded by a rigid bottom. The fields on the boundary are computed by asymptotic ray theory (ART), GBM, and by a rigorous generalized ray integral whose numerical evaluation serves as a reference. It is found that a beam stack “tuned” for accuracy along a ray that has undergone a given number of reflections becomes successively less accurate as the observer moves to a ray segment with a lesser or greater number of reflections. Retuning removes this deficiency but requires again a reference result for comparison. This circumstance illustrates again the basic difficulty with GBM. Possible spectral remedies [Lu, Felsen, and Ruan, Geophys. J. R. Astron. Soc. (1987)] are discussed, but they are less readily computable. [Work supported by NJIT and ONR.]

ISSN:0001-4966    

DOI:10.1121/1.2024514

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Leaky Rayleigh waves propagating along the bottom side of floating sea‐ice plates experience cylindrical geometrical spreading and have their low‐frequency limit determined by the ice plate thickness that corresponds to about 560 Hz. A second type of leaky Rayleigh wave can exist along ice plate edges propagating with no geometrical spreading and has its low‐frequency limit determined by the large plate horizontal dimensions. Laboratory ultrasonic modeling results are presented demonstrating the detection of low‐frequency Rayleigh waves radiated from ice plate edges. In one experiment, the plate‐edge leaky Rayleigh wave wavelength was greater than 12 times the ice plate thickness. The results suggest that a 3‐m‐thick ice plate in the Arctic may easily radiate 10‐ to 100‐Hz components from its edges. The ice plate edge acting nearly as a finite length line source produces high directionality of the radiated leaky Rayleigh wave into the water. The low‐frequency plate‐edge leaky Rayleigh waves may be detected in the water at significant distances from the ice edge. Additional physical insights into the controversial leaky Rayleigh wave are provided by comparing water/ice and Freon‐113/ice interface conditions where a high‐density low‐velocity liquid is used. [Work supported by ONR.]

ISSN:0001-4966    

DOI:10.1121/1.2024089

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP