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May 1987

Volume 81, Issue S1, pp. S1-S100

Page 1 of 18 Pages Return to All Sections Next Page
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back to top Session A. Speech Communication I: Speech Perception
Contributed Papers
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The problem of serial order in auditory word recognition (A)

Howard C. Nusbaum, Steven L. Greenspan, and Mathew Jensen

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S1-S1 (1987); (1 page)

Online Publication Date: 13 Aug 2005

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Recently, there has been a resurgence of interest in parallel distributed processing models of human perception. When speech perception is modeled in this type of spatially distributed network, a problem arises in coding the temporal order of perceptual units such as phonemes or words. In general, three solutions to this problem have been proposed: First, perceptual units may be context coded such as in context‐sensitive allophones. The order of units presented at different points in time can be determined by matching the context “edges” of each activated unit. Second, different portions of the network may represent different time frames. By this approach, the recognition of each successive perceptual unit activates representations in successive segments of the network. Finally, temporal order may be represented in the computational dynamics of the network. In this case, expectations about serial order are used to shift the focus of processing attention within the network. Thus, while the first two approaches recode temporal order into a spatial or spatial‐like representation, the third uses a temporal representation. Each of these approaches has positive and negative attributes, the implications of which will be discussed for a neuromorphic theory of speech perception. [Work supported, in part, by NIH.]
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The neighborhood activation model of auditory word recognition (A)

Paul A. Lute

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S1-S1 (1987); (1 page)

Online Publication Date: 13 Aug 2005

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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.]
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Auditory word recognition is not more sensitive to word‐initial than to word‐final stimulus information (A)

M. J. van der Vlugt and S. G. Nooteboom

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S2-S2 (1987); (1 page)

Online Publication Date: 13 Aug 2005

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Several accounts of the human recognition of spoken words assign special importance to stimulus‐word onsets. The experiment described here was designed to find out whether such a word‐beginning superiority effect is due to a special sensitivity of the word recognition process to word‐initial stimulus information, or rather to the special importance of word onsets for the proper alignment of stimuli with word candidates. Twenty‐eight polysyllabic monomorphematic test words were selected, all having the special characteristic that their left‐to‐right and right‐to‐left recognition points coincided in the same phoneme. These words were synthesized from diphones, and, of each word, four versions were prepared: (a) without noise; (b) with noise masking segment perception in the word‐initial fragment; (c) with noise masking segment perception in the word‐final fragment; and (d) with noise masking the whole word. These stimuli were, appropriately blocked, distributed over four stimulus tapes, and presented to four groups of 12 subjects for word recognition. Percentages correctly recognized real words were, for the four conditions: (a) 89%, (b) 54%, (c) 59%, and (d) 13%. The difference between (b) and (c) was not significant. This is interpreted as evidence that (1) auditory word recognition is not more sensitive to word‐initial than to word‐final stimulus information, and (2) stimulus information from all parts of a spoken word can be used efficiently, as long as its proper time alignment with word candidates in the mind of the listener is ensured.
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Effects of talker uncertainty I: Auditory word recognition (A)

John W. Mullennix, David B. Pisoni, and Christopher S. Martin

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S2-S2 (1987); (1 page)

Online Publication Date: 13 Aug 2005

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The production and resulting acoustic composition of spoken words vary as functions of individual talker characteristics. However, the effects of talker differences on auditory word recognition processes have been largely ignored by researchers working in speech perception. In the present study, the effects of talker differences on perception of spoken words were examined by manipulating two factors: talker uncertainty (i.e., words produced from a single talker or from 15 talkers) and lexical structure (i.e., high‐ or low‐density lexical items). In the first experiment, identification performance for words presented in noise was worse when the items were produced by different talkers, than by a single talker. In the second experiment, latencies and accuracy in a naming task were also worse under multiple‐talker condition. In both experiments, lexical density alone did not have a significant effect on performance. The relationship of these results to the underlying processing operations involved in auditory word recognition will be discussed. [Work supported by NIH.]
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Effects of talker uncertainty II: Encoding speech into memory (A)

Christopher S. Martin and John W. Mullennix

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S2-S2 (1987); (1 page)

Online Publication Date: 13 Aug 2005

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Individual talkers vary in a large number of articulatory and acoustic characteristics. Little research has been conducted concerning the effects of talker uncertainty on encoding speech into memory. In order to examine this problem, a serial‐ordered recall experiment was conducted. The stimuli were CVC monosyllabic English words produced by different male and female talkers. Listeners were presented with lists of ten items produced by a singler talker or lists of ten items produced by multiple talkers, and were required to recall the items in the order presented. Percent correct recall in the primary region of the serial position curve was lower as the amount of talker variability within the lists increased. The result suggest that the encoding of speech into memory is affected by uncertainty from trial to trial due to talker variability. The hypothesis that perceptual processes involved in talker normalization are located at an auditory‐to‐phonetic level will be discussed. [Work supported by NIH.]
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The lexical status effect on place of articulation and voice onset time contrasts (A)

Marjorie A. Reed

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S2-S2 (1987); (1 page)

Online Publication Date: 13 Aug 2005

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Ganong [J. Exp. Psychol.: Hum. Percept. Perform. 6, 110–125 (1980)] first reported that the presence of a word at one end of a voice onset time series influenced the classification of stimuli near the boundary. Fox [Percept. Psychophys. 34, 526–540 (1983)] reported a similar effect using place of articulation stimuli. In the present experiment, the lexical status effect on two voice onset time continuua (/bot/ to /pot/ and /bok/ to /pok/) was compared to that on two place of articulation continuua (/bon/ to /don/ and /bop/ to /dop/). Results showed effects of lexical status for both types of stimuli. Ambiguous tokens near the category boundary were perceived in favor of the word, while the classification of endpoint stimuli was not influenced. The lexical status effect was significantly larger for voice onset time stimuli than for place of articulation stimuli. This difference may result from the time required for the lexical status effect to develop, suggesting alternate interpretation of Fox's data on the time course of the effect. Implications for interactive and separate stage models are discussed.
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Context effects in spoken language (A)

Robert Pedlow

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S2-S2 (1987); (1 page)

Online Publication Date: 13 Aug 2005

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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.
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Perceptual differentiation of spontaneous and read utterances after resynthesis with monotone fundamental frequency (A)

R. E. Remez, R. S. Bressel, P. E. Rubin, and N. Ren

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S2-S3 (1987); (2 pages)

Online Publication Date: 13 Aug 2005

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Our prior research revealed that naive listeners can differentiate spontaneous speech and read speech even when lexical, syntactic, and semantic components are equated in the two modes of production. On a typical trial in our tests, a listener hears a pair of excerpts identical in these three levels of description, taken from a spontaneous and a read monologue produced by the same talker. The perceptual task is to identify the spontaneously produced member of the pair. In the present case, LPC resynthesis was employed to create constant F0 versions of highly differentiable pairs of sentences, to test our working hypothesis that the variation of F0 serves as the most reliable index of perceptual performance. Three conditions were tested: whole sentence comparisons, initial‐half‐sentence comparisons, and final‐half‐sentence comparisons. Subjects performed above chance when listening to whole sentences only, indicating the existence of residual information for production mode in the absence of F0 variation. Implications and extensions of this finding will be discussed, [Work supported by NINCDS and NICHHD.]
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Forward recognition masking: Another look at the “Echo” (A)

Gail R. Tomiak

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S3-S3 (1987); (1 page)

Online Publication Date: 13 Aug 2005

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Auditory backward recognition masking effects have been interpreted as reflecting the existence of an echoic memory: an unencoded sensory store whose contents decay rapidly and are easily overwritten by succeeding auditory stimulation. However, it is equally likely that masking effects reflect the time course of an early stage of auditory processing. To distinguish these alternative conceptualizations, vowel stimuli were used in a forward recognition masking procedure. The interstimulus interval (ISI) remained constant, while the mask duration (and hence the stimulus‐onset asynchrony, SOA) was varied. The simple storage model predicts that the efficacy of a mask is a function of the time between mask offset and target onset (ISI). Since this interval was constant, equal masking effects would be expected at all SOA intervals. The perceptual processing view predicts that target recognition performance would improve with increasing mask duration (increasing SOA). As mask duration/SOA increases, it is likely that processing of the mask would be completed before target onset. The results, and the implications of these findings, will be discussed. [Work supported by NINCDS.]
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Release burst masking effects for temporal order identification (A)

Richard E. Pastore, Jody K. Layer, Robert J. Logan, and Crystle B. Morris

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S3-S3 (1987); (1 page)

Online Publication Date: 13 Aug 2005

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Nearly three decades ago, Hirsh [J. Acoust. Soc. Am. 31, 759–761 (1959)] found that the threshold for identification of temporal order of onset is significantly longer than the threshold for detection of onset asynchrony, and proposed that the order identification threshold might serve as a basis for the contrast between voiced and unvoiced aspirated stop consonants in initial position. In the last decade, a number of researchers have argued that temporal order identification threshold does not play a significant role in voicing contrast. One basis for this argument against a phonetic perception role is that the 15‐ to 20‐ms range of typical order identification thresholds for simple stimuli are significantly shorter than VOT boundaries typical for synthetic stop consonants which include an initial release burst. The current research investigated the possible contribution of an initial noise burst analog as a masking stimulus. The initial noise burst shifts temporal order identification thresholds to significantly longer onset asynchronies which are equivalent in magnitude to VOT voicing contrast boundaries.
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Perception of onset bursts in /ba da ga/ syllables by good and poor readers (A)

Judith A. Parker

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S3-S3 (1987); (1 page)

Online Publication Date: 13 Aug 2005

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In identification and discrimination tasks, good and poor readers listened to tapes of synthesized stimuli consisting of 350‐ms full (burst + formant transition) and partial (formant transition only) acoustic signals for voiced stop CV syllables. A free identification procedure was used to elicit percepts and an oral response method was used to avoid possible reading/writing confounds. The ANOVA, probit analysis, and signal detection analysis were used to evaluate findings. As a group, poor readers demonstrated significantly weaker categorical perception for the /da ga/ boundary in stimuli lacking bursts. Burstless signals produced severe problems for some poor readers; others performed similarly to the higher averaged performances of the good readers. Individual differences were noted: impaired perception regarding place, manner, or boundaries occurred in the full‐stimulus condition, and more often for the partial condition. The data are relevant to theories that propose a hierarchy of acoustic cues for the perception of linguistic contrasts and also suggest a possible perceptual deficit that may be involved in some forms of dyslexia.
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Effects of preceding context on perception of voice onset time (A)

Bruno H. Repp

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S3-S3 (1987); (1 page)

Online Publication Date: 13 Aug 2005

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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.]
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Evaluation of the constant ratio rule for consonant confusions (A)

Theodore S. Bell, Donald D. Dirks, and Gail E. Kincaid

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S3-S3 (1987); (1 page)

Online Publication Date: 13 Aug 2005

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The constant‐ratio rule for consonant confusions asserts that the ratio of errors of any consonant to any others remains constant regardless of the size of the matrix from which the cells were chosen. In this study, log‐linear models were applied to test the constant‐ratio rule. Normal‐hearing young adults were presented various closed‐set arrangements of syllable tokens, spoken by a male and female speaker, and selected from a set of 14 VCs each paired with the vowel /ɑ/. Stop consonants and fricatives, both voiced and voiceless, were presented at three presentation levels as isolated sets (by feature) and in combination. The relationships among voiceless stop consonants remained constant irrespective of the size and nature of the response foil. Similarly, voiceless fricatives were unaffected by the nature of the closed set. In contrast, patterns of errors among voiced stops were dependent on the set of alternatives, as were voiced fricatives. Speaker differences, individual differences among listeners, and implications relating to the generalizability of confusion data collected in small closed‐set arrangements are also discussed. [Work supported by a grant from NINCDS.]
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Effects of message redundancy on the calculations of speech intelligibility (A)

Chaslav V. Pavlovic

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S4-S4 (1987); (1 page)

Online Publication Date: 13 Aug 2005

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The articulation index methods used today assume that the distribution over frequency of the usable information content of speech does not depend on various sequential or contextual constraints existing in the message. This assumption has repeatedly been shown to be inaccurate, but the suggested alternative approaches reduce the generality of the theory. They require a separate frequency importance function for each degree of redundancy. In this study, the frequency importance function for the material of average everyday redundancy is derived. The function is flat on the Bark scale. This suggests that the speech code is optimally matched to the receiver (auditory system). The optimization refers to maximizing the reception rate of information.
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Response time to a sentence verification task as a function of LPC narrow‐band processing and bit error rate (A)

A. chmidt‐Nielsen and Howard J. Kallman

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S4-S4 (1987); (1 page)

Online Publication Date: 13 Aug 2005

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The comprehension of narrow‐band digital speech with bit errors was tested using a sentence verification task. The difficulty of the verification task was varied by using predicates that were either strongly or weakly related to the subjects. (A toad has warts./A toad has eyes.) In addition, half of the sentences were about category relationships, and half were about property relationships. (A salmon is a bird./A camel has horns.) The test conditions included unprocessed speech and speech processed using a 2400 bit/s linear predictive coding (LPC) voice processing algorithm with random bit error rates of 0%, 2%, and 5%. In general, response accuracy decreased and reaction time increased with LPC processing and with increasing bit error rates. False sentences took longer to verify than did true sentences, but there were fewer errors for the false sentences. Weakly related true sentences and strongly related false sentences were more difficult than their counterparts. Interactions between sentence type and processing conditions will be discussed.
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Perception of natural and vocoded sentences among English monolinguals and German‐English bilinguals (A)

Molly Mack

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S4-S4 (1987); (1 page)

Online Publication Date: 13 Aug 2005

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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. I 77, 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.]
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Listener‐talker interaction: Is there an “autophonetic” effect? (A)

John W. Hawks and James D. Miller

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S4-S4 (1987); (1 page)

Online Publication Date: 13 Aug 2005

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Based on recent physiological evidence for neural selectivity to self‐produced song in the auditory system of the White‐Crowned Sparrow, a hypothesis stating that the human perceptual mechanism for speech may be most acute for self‐produced speech sounds was tested. A test of the ability to identify monosyllabic words was presented in a noise background. The same subjects served as both talkers and listeners. A small, but statistically nonsignificant, advantage is found when listener and talker are the same person. Additionally, while variation between talkers was nearly twice the variation between listeners, the performance of a particular talker‐listener pair could be predicted by a simple equation. This equation gives equal weight to the talker's and listener's average performance, and thus the talkers, by virtue of their greater variance, tend to have a greater influence. [Work supported by NIH.]
back to top Session B. Noise I and Psychological and Physiological Acoustics I: History and Development of Hearing Protection Devices
Invited Papers
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History and development of hearing protection devices (A)

W. Ian Acton

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S4-S5 (1987); (2 pages)

Online Publication Date: 13 Aug 2005

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Military need has spurred the invention of hearing protector since the times of Greek mythology. Earplugs were patented in 1864 and canal caps attached to an adjustable headband in 1884 as protection for soldiers and sailors. Attempts to limit gunfire noise by mechanical devices commenced in 1905, leading to Mallock‐Armstrong plugs for use in the First World War. Disposable earplugs were patented in 1914 also. Systematic development of earplugs for forces during the Second World War culminated in the V‐51R. Leather flaps over the ears were supposed to protect the crews of military aircraft. The increased noise of jet engines led to the production of recognizable earmuffs, although the stiffness of the cushions required a strong headband to ensure a seal against the head. This caused a vicelike grip. The problem was overcome with the development of fluid‐filled cushions by Shaw in 1954. Progress has continued towards comfort and acceptability, with glass‐down appearing in the late 1950's, conformable foam plugs in the 1970's, and nonlinear electronic systems incorporated into muffs in the 1980's.
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Analytical concepts and models for calculating hearing protector attenuation (A)

Edgar A. G. Shaw

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S5-S5 (1987); (1 page)

Online Publication Date: 13 Aug 2005

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In principle, the ideal hearing protector is a rigid airtight cover or plug that encloses a volume of air in contact with the eardrum and is sealed to an immovable object (the head or the external ear) by a resilient airtight cushion or interface. According to this simple view, the sound attenuation curve is solely dependent on a few lumped elements: the mass and area of the cover or plug, the acoustic impedance presented by the enclosed space, and the stiffness and mechanical resistance of the cushion or interface. In practice, the attenuation is also dependent on air leakage, body‐conducted sound, the lack of rigid support, wave effects, and mechanical imperfections. These factors and others have been measured, estimated, and modeled with considerable success though perfect agreement between theory and experiment remains elusive. So, perhaps there is still room for further work of a fundamental nature. In the meantime, despite their limitations, the classical analytical models continue to provide an invaluable foundation for hearing protector design.
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Development of a unique passive level‐dependent hearing protector (A)

C. H. Allen and E. H. Berger

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S5-S5 (1987); (1 page)

Online Publication Date: 13 Aug 2005

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The need for protection of hearing against intermittent high‐level sounds and the opposite need for retaining hearing sensitivity during low‐level intervals, have led to the development of level‐dependent, commonly called “nonlinear,” hearing protectors. This paper deals with the design and refinement of passive means for automatically and instantaneously altering the amount of attenuation, provided at the ear, in response to the incident sound level. The early successful development of a nonlinear earplug for protection against gunfire is followed through laboratory and field tests, and the advantages and limitations of such an earplug are discussed. The more recent application of a nonlinear orifice to earmuffs, for various applications, introduces several new difficulties. Their identification and the means that have been found suitable for use in practical level‐dependent earmuffs are discussed. Test data are presented showing acoustic characteristics over a range of incident sound levels from 100 dB, or lower, to 160 dB, or higher. Results obtained with steady state, broadband, and narrow‐band noise are compared and are shown to be similar to results obtained with impulse noise, such as experienced, for example, from gunshots or forging hammers.
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History and development of active noise reduction hearing protection (A)

Richard L. McKinley

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S5-S5 (1987); (1 page)

Online Publication Date: 13 Aug 2005

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Ever since Lueg's 1936 patent, the application of active noise reduction technology to hearing protection has been a goal of numerous research groups. This paper will describe the various efforts to apply active noise reduction technology to earcups over the time span from 1936 through the present. Each of the various efforts will be described in terms of basic cancellation technique, hardware realization, and both laboratory and field performance when available. In addition, a working model of the current active noise reduction headset developed jointly by the Air Force and Bose Corporation, similar to the unit used on the around the world flight of the Voyager, will be presented.
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Noise attenuating earphones for audiometric testing (A)

Mead C. Killion and Elliott H. Berger

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S5-S5 (1987); (1 page)

Online Publication Date: 13 Aug 2005

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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.
Contributed Papers
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Hearing protector attenuation for impulse noise (A)

S. E. Forshaw

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S6-S6 (1987); (1 page)

Online Publication Date: 13 Aug 2005

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The study of the effectiveness of hearing protection for impulse noise pose several problems. Due to the transient nature of the noise, real‐ear‐at‐threshold (REAT) data are not readily applicable since current impulse‐noise criteria are based on either (1) peak pressure, some measure of impulse duration, and the number of impulses, or (2) total A‐weighted energy. It is possible to measure the effect of an earmuff on these parameters by positioning a miniature transducer under the muff at the wearer's ear canal. An alternative arrangement which permits the study of both ear muffs and plugs involves the use of an acoustic test fixture. The test fixture must simulate those characteristics of the head and outer and middle ears that affect the attenuation of hearing protectors on real ears. These include the viscoelastic characteristics of the circumaural and intra‐aural skin, the inertial properties of the head, the frequency response of the auditory canal, and the mechanisms of bone conduction and physiological masking. DCIEM has sponsored by contract the development of such a test fixture [C. Giguere et al., J. Acoust. Soc. Am. Suppl. 1 78, S5 (1985)]. Attenuation results with the test fixture compare reasonably well with REAT‐derived data. Agreement between the two methods could be improved for earplugs if the thickness of the artificial intra‐aural skin were reduced. On‐going research is directed towards studying human intra‐aural skin, and measuring the peak attenuation, waveform‐duration increase, and linear and A‐weighted energy reduction of protectors for short‐ and long‐duration impulses.
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The development of hearing protective systems for use in the high‐noise environments of army combat vehicles (A)

Mitchell S. Mayer and Tat Y. Fung

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S6-S6 (1987); (1 page)

Online Publication Date: 13 Aug 2005

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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.
back to top Session C. Psychological and Physiological Acoustics II: Cochlea, VIII Nerve, and Evoked Responces
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Tectorial membrane: Static mechanical properties in vivo (A)

Jozef J. Zwislocki, Steven C. Chamberlain, and Norma B. Slepecky

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S6-S6 (1987); (1 page)

Online Publication Date: 13 Aug 2005

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In a mammalian cochlea, stimulation of the hair cells must be associated with shear motion between the organ of Corti and the tectorial membrane. Knowledge of the mechanical properties of the tectorial membrane in its natural environment is essential for our understanding of this process. Recently, the present authors have been able to visualize the tectorial membrane in live Mongolian gerbils by fenestrating the scala media of the second cochlear turn without disturbing Reissner's membrane. The anatomical configuration of the cochlea in these animals allowed us to observe the tectorial membrane over its entire width. A micropipette was inserted into the membrane and moved radially and longitudinally approximately parallel to the membrane surface. When vitally stained with Janus green, the membrane showed astonishing toughness and resilience in both directions. Its deformation patterns resembled those of a rubber band. When vitally stained with Alcian blue, its tensile strength was decreased, and it tore rather easily. Subsequent microscopic investigation of the membrane in vitro showed that the two stains bind to different structures.
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