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Journal of the Acoustical Society of America

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Jul 1987

Volume 82, Issue 1, pp. 1-409

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Stimulus intensity and loudness recruitment: Neural correlates

D. P. Phillips

J. Acoust. Soc. Am. Volume 82, Issue 1, pp. 1-12 (1987); (12 pages) | Cited 5 times

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An abnormally rapid rate of loudness growth for given increments in stimulus intensity is seen both in patients with cochlear pathology and in normal listeners under conditions of wide‐spectrum noise masking. The phenomenological similarity between these psychophysical observations raises the question of whether a single mechanism, or set of mechanisms, underlies them. Recent neurophysiological studies in animals have addressed the effects of cochlear pathology and noise masking on the neural correlates of stimulus intensity in the central auditory nervous system. A comparison of the data presented in those studies reveals that there are sequelae of cochlear pathology seen in the discharges of auditory‐nerve fibers that might reasonably be expected to contribute to a steepened loudness function. These sequelae are not seen at the same locus in normal animals studied with noise masking paradigms. Noise masking, however, may have effects on the tonal sensitivity of more central neurons that mimic some of the sequelae of cochlear pathology seen in the auditory nerve. These data suggest that the mechanisms underlying the two manifestations of recruitment may be quite different, one having a uniquely cochlear site, while the other reflects purely central processes.
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43.10.Ln Surveys and tutorial papers relating to acoustics research; tutorial papers on applied acoustics
43.64.Nf Cochlear electrophysiology
43.66.Cb Loudness, absolute threshold
43.64.Qh Electrophysiology of the auditory central nervous system

Analytical and experimental investigation on vibrating circular plates with stepped thickness over a concentric circular region

D. Avalos, Patricio A. A. Laura, and A. M. Bianchi

J. Acoust. Soc. Am. Volume 82, Issue 1, pp. 13-16 (1987); (4 pages)

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Transverse vibrations of the structural elements described in the title are studied for the case where the edges are elastically restrained against translation and rotation. Since finding an exact solution is a difficult task, it was considered convenient to approximate the response of the plate in the case of free, axisymmetric vibrations by means of a summation of simple polynomial coordinate functions that satisfy the governing boundary conditions. The Ritz method is used in order to generate the frequency equation. The natural frequency coefficients are optimized by minimizing each eigenvalue with respect to an undetermined exponential parameter included in each coordinate function.
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43.38.Fx Piezoelectric and ferroelectric transducers
43.40.Dx Vibrations of membranes and plates
43.20.Bi Mathematical theory of wave propagation

Instantaneous and time‐averaged energy transfer in acoustic fields

J. Adin Mann, III, Jiri Tichy, and Anthony J. Romano

J. Acoust. Soc. Am. Volume 82, Issue 1, pp. 17-30 (1987); (14 pages) | Cited 11 times

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The fundamentals of energy transfer in an acoustic field are addressed and it is shown that describing the flux of energy in an acoustic field with the active intensity alone is inaccurate. A single active intensity vector describes only the time‐average energy flux at a point in space, but not where the energy came from nor where it is going. Consequently, the instantaneous intensity must be used to properly describe energy flux as a time‐dependent process. The phenomenon of the acoustic vortex is examined and, from the perspective of active intensity, it is seen to represent a resultant wave rotating around a zero pressure line or point at which the pressure phase is discontinuous. It is shown that this resultant wave travels with a phase speed cp, which is generally different than the plane‐wave phase speed c. The instantaneous intensity, however, shows that energy is flowing through the vortex and not with the resultant waves. Although the complex intensity vector is normally separated into the active and reactive components (i.e., rotational and solenoidal parts), the active intensity can be further represented by two parts, one with zero and another with nonzero curl, which permits the representation of the coupling between sources or parts of a source. In general, this article emphasizes the physical meaning and interpretation of energy related quantities.
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43.58.Fm Sound level meters, level recorders, sound pressure, particle velocity, and sound intensity measurements, meters, and controllers
43.20.Ye Measurement methods and instrumentation
43.20.Bi Mathematical theory of wave propagation

Discrimination in neonates of very short CVs

Josiane Bertoncini, Ranka Bijeljac‐Babic, Sheila E. Blumstein, and Jacques Mehler

J. Acoust. Soc. Am. Volume 82, Issue 1, pp. 31-37 (1987); (7 pages)

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The experiment reported here explores the ability of 4‐ to 5‐day‐old neonates to discriminate consonantal place of articulation and vowel quality using shortened CV syllables similar to those used by Blumstein and Stevens [J. Acoust. Soc. Am. 67, 648–662 (1980)], without vowel steady‐state information. The results show that the initial 34–44 ms of CV stimuli provide infants with sufficient information to discriminate place of articulation differences in stop consonants ([ba] vs [da], [ba] vs [ga], [bi] vs [di], and [bi] vs [gi]) and following vowel quality ([ba] vs [bi], [da] vs [di], and [ga] vs [gi]). These results suggest that infants can discriminate syllables on the basis of the onset properties of CV signals. Furthermore, this experiment indicates that neonates require little or no exposure to speech to succeed in such a discrimination task.
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43.71.An Models and theories of speech perception
43.71.Es Vowel and consonant perception; perception of words, sentences, and fluent speech

Acoustic parameters measured by a formant‐estimating speech processor for a multiple‐channel cochlear implant

P. J. Blamey, R. C. Dowell, G. M. Clark, and P. M. Seligman

J. Acoust. Soc. Am. Volume 82, Issue 1, pp. 38-47 (1987); (10 pages) | Cited 1 time

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In order to assess the limitations imposed on a cochlear implant system by a wearable speech processor, the parameters extracted from a set of 11 vowels and 24 consonants were examined. An estimate of the fundamental frequency EF0 was derived from the zero crossings of the low‐pass filtered envelope of the waveform. Estimates of the first and second formant frequencies EF1 and EF2 were derived from the zero crossings of the waveform, which was filtered in the ranges 300–1000 and 800–4000 Hz. Estimates of the formant amplitudes EA1 and EA2 were derived by peak detectors operating on the outputs of the same filters. For vowels, these parameters corresponded well to the first and second formants and gave sufficient information to identify each vowel. For consonants, the relative levels and onset times of EA1 and EA2 and the EF0 values gave cues to voicing. The variation in time of EA1, EA2, EF1, and EF2 gave cues to the manner of articulation. Cues to the place of articulation were given by EF1 and EF2. When pink noise was added, the parameters were gradually degraded as the signal‐to‐noise ratio decreased. Consonants were affected more than vowels, and EF2 was affected more than EF1. Results for three good patients using a speech processor that coded EF0 as an electric pulse rate, EF1 and EF2 as electrode positions, and EA1 and EA2 as electric current levels confirmed that the parameters were useful for recognition of vowels and consonants. Average scores were 76% for recognition of 11 vowels and 71% for 12 consonants in the hearing‐alone condition. The error rates were 4% for voicing, 12% for manner, and 25% for place.
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43.71.Ky Speech perception by the hearing impaired
43.72.Ar Speech analysis and analysis techniques; parametric representation of speech
43.66.Ts Auditory prostheses, hearing aids
43.70.Jt Instrumentation and methodology for speech production research

Vowel and consonant recognition of cochlear implant patients using formant‐estimating speech processors

P. J. Blamey, R. C. Dowell, A. M. Brown, G. M. Clark, and P. M. Seligman

J. Acoust. Soc. Am. Volume 82, Issue 1, pp. 48-57 (1987); (10 pages) | Cited 7 times

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Vowel and consonant confusion matrices were collected in the hearing alone (H), lipreading alone (L), and hearing plus lipreading (HL) conditions for 28 patients participating in the clinical trial of the multiple‐channel cochlear implant. All patients were profound‐to‐totally deaf and ‘‘hearing’’ refers to the presentation of auditory information via the implant. The average scores were 49% for vowels and 37% for consonants in the H condition and the HL scores were significantly higher than the L scores. Information transmission and multidimensional scaling analyses showed that different speech features were conveyed at different levels in the H and L conditions. In the HL condition, the visual and auditory signals provided independent information sources for each feature. For vowels, the auditory signal was the major source of duration information, while the visual signal was the major source of first and second formant frequency information. The implant provided information about the amplitude envelope of the speech and the estimated frequency of the main spectral peak between 800 and 4000 Hz, which was useful for consonant recognition. A speech processor that coded the estimated frequency and amplitude of an additional peak between 300 and 1000 Hz was shown to increase the vowel and consonant recognition in the H condition by improving the transmission of first formant and voicing information.
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43.71.Ky Speech perception by the hearing impaired
43.72.Ar Speech analysis and analysis techniques; parametric representation of speech
43.66.Ts Auditory prostheses, hearing aids
43.71.Es Vowel and consonant perception; perception of words, sentences, and fluent speech

An acoustic analysis of fluctuations in the voices of normal adult speakers across three times of day

Kathryn L. Garrett and E. Charles Healey

J. Acoust. Soc. Am. Volume 82, Issue 1, pp. 58-62 (1987); (5 pages) | Cited 1 time

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The purpose of this study was to determine the amount of variation for several vocal parameters across three times of the day (morning, noon, and afternoon). Connected speech samples from normal adult males (N=10) and females (N=10) were recorded during morning, early afternoon, and late afternoon. Results showed that males produced a statistically significant increase in speaking fundamental frequency (SFF) from morning to afternoon. Females did not demonstrate a statistically significant change in SFF across the three time periods. Vocal amplitude did not change significantly for either group. The SFF variability was higher for the females than for the males. Analysis of individual data revealed that the patterns of vocal change across the three times of day were not consistent among the subjects.
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43.70.Aj Anatomy and physiology of the vocal tract, speech aerodynamics, auditory kinetics
43.70.Fq Acoustical correlates of phonetic segments and suprasegmental properties: stress, timing, and intonation

Effects of changes in absolute signal level on psychophysical tuning curves in quiet and noise in patas monkeys

D. W. Smith, D. B. Moody, and W. C. Stebbins

J. Acoust. Soc. Am. Volume 82, Issue 1, pp. 63-68 (1987); (6 pages)

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Forward masking psychophysical tuning curves (PTCs) were measured in patas monkeys (Erythrocebus patas) at 2, 4, and 8 kHz at signal levels of 10, 30, and 60 dB SL in quiet, and at 10 dB above masked threshold in two levels of wideband noise. Absolute signal levels with masking approximated those at 30 and 60 dB SL in quiet. Results in quiet agree with those reported in the literature, demonstrating broadening of the PTC as signal level is increased. The PTCs measured in noise also demonstrated a similar broadening, or loss of selectivity, at higher SPLs. These later findings differ from those of a previous study [D. M. Green, B. R. Shelton, M. C. Picardi, and E. R. Hafter, J. Acoust. Soc. Am. 69, 1758–1762 (1981)] which used maskers to control the broadened excitation pattern in humans at levels of up to 34 dB above threshold. Differences in findings might be attributed to higher SPLs used in the present study. The data taken in noise backgrounds are not consistent with explanations for broadening based on an increase in the width of excitation patterns, but instead support the suggestion that the filter itself is nonlinear. Moreover, comparisons of PTCs in quiet and noise suggest that ‘‘off‐frequency’’ listening acts at any given measurement level to artificially sharpen PTCs.
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43.66.Ba Models and theories of auditory processes
43.66.Dc Masking
43.66.Fe Discrimination: intensity and frequency
43.66.Gf Detection and discrimination of sound by animals

Factors affecting thresholds for sinusoidal signals in narrow‐band maskers with fluctuating envelopes

Brian C. J. Moore and Brian R. Glasberg

J. Acoust. Soc. Am. Volume 82, Issue 1, pp. 69-79 (1987); (11 pages) | Cited 18 times

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When a signal is higher in frequency than a narrow‐band masker, thresholds are lower when the masker envelope fluctuates than when it is constant. This article investigates the cues used to achieve the lower thresholds, and the factors that influence the amount of threshold reduction. In experiment I the masker was either a sinusoid (constant envelope) or a pair of equal‐amplitude sinusoids (fluctuating envelope) centered at the same frequency as the single sinusoid (250, 1000, 3000, or 5275 Hz). The signal frequency was 1.8 times the masker frequency. At all center frequencies, thresholds were lower for the two‐tone masker than for the sinusoidal masker, but the effect was smaller at the highest and lowest frequencies. The reduced effect at high frequencies is attributed to the loss of a cue related to phase locking in the auditory nerve. The reduced effect at low frequencies can be partly explained by reduced slopes of the growth‐of‐masking functions. In experiment II the masker was a sinusoid amplitude modulated at an 8‐Hz rate. Masker and signal frequencies were the same as for the first experiment. Randomizing the modulation depth between the two halves of a forced‐choice trial had no effect on thresholds, indicating that changes in modulation depth are not used as a cue for signal detection. Thresholds in the modulated masker were higher than would be predicted if they were determined only by the masker level at minima in the envelope, and the threshold reduction produced by modulating the masker envelope was less at 250 Hz than at higher frequencies. Experiments III and IV reveal two factors that contribute to the reduced release from masking at low frequencies: (1) The rate of increase of masked threshold with decreasing duration is greater at 250 Hz than at 1000 Hz; (2) the amount of forward masking, relative to simultaneous masking, is greater at 250 Hz than at 1000 Hz. The results are discussed in terms of the relative importance of across‐channel cues and within‐channel cues.
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43.66.Dc Masking
43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music
43.66.Ba Models and theories of auditory processes

Effects of auditory fatigue on psychophysical estimates of cochlear nonlinearities

Susan J. Norton and John B. Mott

J. Acoust. Soc. Am. Volume 82, Issue 1, pp. 80-87 (1987); (8 pages)

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Two‐tone‐suppression (2TS) effects and cubic‐difference‐tone (CDT) levels were measured using a forward‐masking procedure, before and after exposure to an intense tonal stimulus. Changes in 2TS effects were consistent with a change in the nonlinearity, such that the system became more linear, in addition to changes due to attenuation of the primary stimuli F1 and F2. Changes in CDT levels could be accounted for on the basis of a temporary threshold shift at F1 and F2. These results indicate at least a partial dissociation of the mechanisms underlying 2TS and CDT generation.
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43.66.Dc Masking
43.66.Ed Auditory fatigue, temporary threshold shift
43.66.Ki Subjective tones

The perceptual attack time of musical tones

John W. Gordon

J. Acoust. Soc. Am. Volume 82, Issue 1, pp. 88-105 (1987); (18 pages) | Cited 3 times

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Perceptual attack time (PAT) is defined as the time a tone’s moment of attack or most salient metrical feature is perceived relative to its physical onset. Experiments are described that measured the PATs of recorded orchestral instrument tones by means of an interactive procedure with a computer and digital music synthesizer. Some PAT prediction models were then developed and tested against the empirical data. The most successful model had a correlation of 0.995 between measured and predicted PATs. The PAT is dependent on both rise time and listening level, indicating that the slope of the rise function is a key factor. Duration and spectrum can also act as cues to PAT, but are much less influential than amplitude or intensity cues. Possible relations to findings in physiology, particularly to the phenomenon of short‐term adaptation in the firing of auditory fibers, are discussed.
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43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music
43.66.Jh Timbre, timbre in musical acoustics
43.75.Cd Music perception and cognition

Pitch perception by cochlear implant subjects

Brent Townshend, Neil Cotter, Dirk Van Compernolle, and R. L. White

J. Acoust. Soc. Am. Volume 82, Issue 1, pp. 106-115 (1987); (10 pages) | Cited 46 times

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Direct electrical stimulation of the auditory nerve can be used to restore some degree of hearing to the profoundly deaf. Percepts due to electrical stimulation have characteristics corresponding approximately to the acoustic percepts of loudness, pitch, and timbre. To encode speech as a pattern of electrical stimulation, it is necessary to determine the effects of the stimulus parameters on these percepts. The effects of the three basic stimulus parameters of level, repetition rate, and stimulation location on subjects’ percepts were examined. Pitch difference limens arising from changes in rate of stimulation increase as the stimulating rate increases, up to a saturation point of between 200 and 1000 pulses per second. Changes in pitch due to electrode selection depend upon the subject, but generally agree with a tonotopic organization of the human cochlea. Further, the discriminability of such place‐pitch percepts seems to be dependent on the degree of current spread in the cochlea. The effect of stimulus level on perceived pitch is significant but is highly dependent on the individual tested. The results of these experiments are discussed in terms of their impact on speech‐processing strategies and their relevance to acoustic pitch perception.
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43.66.Ts Auditory prostheses, hearing aids
43.66.Fe Discrimination: intensity and frequency
43.66.Hg Pitch

Psychophysical studies relevant to the design of a digital electrotactile speech processor

P. J. Blamey and G. M. Clark

J. Acoust. Soc. Am. Volume 82, Issue 1, pp. 116-125 (1987); (10 pages) | Cited 3 times

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Psychophysical tests were carried out to investigate the perception of electrocutaneous stimuli delivered to the digital nerve bundles. The tests provided data for defining the operating range of a tactile aid for patients with profound‐to‐total hearing loss, as well as the individual differences between subjects and the information that could be transmitted. Monopolar biphasic constant current pulses with variable pulse widths were used. Threshold pulse widths varied widely between subjects and between fingers for the same subject. Thresholds were reasonably stable, but maximum comfortable levels increased with time. Perceived intensity was weakly dependent on pulse rate. Absolute identification of stimuli differing in pulse width gave information transmissions from 1.3–2.1 bits, limited by the dynamic ranges of the stimuli (3–17 dB). Stimuli from electrodes placed on either side of each finger were identified easily by all subjects. Absolute identification of stimuli differing in pulse rate gave information transmissions from 0.5–2.0 bits. Difference limens for pulse rate varied between subjects and were generally poor above 100 pps. On the basis of the results, an electrotactile speech processor is proposed, which codes the speech amplitude as pulse width, the fundamental frequency as pulse rate, and the second formant frequency as electrode position. Variable performances on tasks relying on amplitude and fundamental frequency cues are expected to arise from the intersubject differences in dynamic range and pulse rate discrimination. The psychophysical results for electrotactile stimulation are compared with previously published results for electroauditory stimulation with a multiple‐channel cochlear implant.
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43.66.Wv Vibration and tactile senses
43.71.Rt Sensory mechanisms in speech perception

The application of a capacitive probe technique for direct observation of electromechanical processes in the guinea pig cochlea

Eric L. LePage

J. Acoust. Soc. Am. Volume 82, Issue 1, pp. 126-138 (1987); (13 pages)

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The demonstration of evoked mechanical responses of the outer hair cells in the mammalian cochlea by indirect measurements introduces a new range of problems into direct mechanical measurements. Direct and indirect measurements indicate that the frequency spectra of evoked electromechanical responses may extend well into the range of audio frequencies, revealing a need to develop terminology and protocols for distinguishing evoked mechanical responses from the traditional traveling wave when both are apparently superimposed on the motion of the basilar membrane in the normally functioning cochlea. Details are presented of a frequency‐modulation capacitive probe technique for measurement of vibrating structures of the guinea pig ear. Considerations include the design of the transducer, calibration, sensitivity, linearity, and sources of noise, as well as the influence of the technique upon the animal preparation, and in particular the issues associated with draining scala tympani for the measurement. Relative advantages and disadvantages of the technique are compared with salient features of other techniques currently available. In view of the apparent complexity of cochlear mechanics some preliminary experiments are required to elucidate some of the key questions about reverse‐transduction processes in general. A ‘‘simple’’ first experiment is to test existence of any rectifying or motile response.
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43.64.Kc Cochlear mechanics
43.64.Yp Instruments and methods

Frequency‐dependent self‐induced bias of the basilar membrane and its potential for controlling sensitivity and tuning in the mammalian cochlea

Eric L. LePage

J. Acoust. Soc. Am. Volume 82, Issue 1, pp. 139-154 (1987); (16 pages) | Cited 5 times

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A displacement‐sensitive capacitive probe technique was used in the first turn of guinea pig cochleas to examine whether the motion of the basilar membrane includes a displacement component analogous to the dc receptor potentials of the hair cells. Such a ‘‘dc’’ component apparently exists. At a given location on the basilar membrane, its direction toward scala vestibuli (SV) or scala tympani (ST) varies systematically with frequency of the acoustic stimulus. Furthermore, it appears to consist of two parts: a small asymmetric offset response to each gated tone burst plus a progressive shift of the basilar membrane from its previous position. The mean position shift is cumulative, increasing with successive tone bursts. The amplitude of the immediate offset response, when plotted as a function of frequency, appears to exhibit a trimodal pattern. This displacement offset is toward SV at the characteristic frequency (CF) of the location of the probe, while at frequencies either above or below the CF the offset is relatively larger, and toward ST. The mechanical motion of the basilar membrane therefore appears to contain the basis for lateral suppression. The cumulative mean position shift, however, appears to peak toward ST at the apical end of the traveling wave envelope and appears to be associated with a resonance, not of the basilar membrane motion directly, but coupled to it. The summating potential, measured concurrently at the round window, shows a more broadly tuned peak just above the CF of the position of the probe. This seems to correspond to the peak at the CF of the mechanical bias. As the preparation deteriorates, the best frequency of the vibratory displacement response decreases to about a half‐octave below the original CF. There is a corresponding decrease in the frequency of the peaks of the trimodal pattern of the asymmetric responses to tone bursts. The trimodal pattern also broadens.
In previous experiments the basilar membrane has been forced to move in response to a low‐frequency biasing tone. The sensitivity to high‐frequency stimuli varies in phase with the biasing tone. The amplitudes of slow movement in these earlier experiments and in the present experiments are of the same order of magnitude. This suggests strongly that the cumulative shift toward ST to a high‐frequency acoustic stimulus constitutes a substantial controlling bias on the sensitivity of the cochlea in that same high‐frequency region. Its effect will be to reduce the slope of neural rate‐level functions on the high‐frequency side of CF.
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43.64.Kc Cochlear mechanics
43.64.Yp Instruments and methods
43.64.Bt Models and theories of the auditory system

A spatial template for the shape of tuning curves in the mammalian cochlea

Eric L. LePage

J. Acoust. Soc. Am. Volume 82, Issue 1, pp. 155-164 (1987); (10 pages) | Cited 1 time

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The shape of the tuning curve of primary auditory neurons of four mammals is characterized using a simple exponential model. The regression analysis formalizes a distinction between the characteristic frequency of a neuron and its ‘‘nominal’’ characteristic frequency in cases of temporary threshold loss in high‐frequency neurons. Second, the model offers a stronger quality test for sharpness of tuning than the Q10 dB since it takes into account the threshold of the neuron at its characteristic frequency and its ‘‘characteristic place’’ of origin along the cochlear partition. Third, the model reveals that the low‐frequency side of the tip segment of the tuning curve is bounded by a constraint or template which is most simply expressed in spatial terms. The template describes the basal‐side boundary of an ‘‘excitatory region’’ whose length along the cochlear partition is proportional to the square root of the sound pressure. Tuning curve variability arises because biological dependencies influence the basic template. A ‘‘spatial‐filter’’ hypothesis is developed and its generality is discussed, particularly in regard to the case of the acoustic ‘‘fovea’’ of the horseshoe bat. Finally, the possibility is discussed that the template possesses a simple physiological correlate in the form of a spatially localized region marked by a ‘‘dc’’ shift of the mean position of the basilar membrane which sets the sensitivity of the tuning mechanism [E. L. LePage, J. Acoust. Soc. Am. 82, 139–154 (1987)].
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43.64.Kc Cochlear mechanics

Potentials evoked by the sinusoidal modulation of the amplitude or frequency of a tone

Terence W. Picton, Christopher R. Skinner, Sandra C. Champagne, Adrian J. C. Kellett, and Anita C. Maiste

J. Acoust. Soc. Am. Volume 82, Issue 1, pp. 165-178 (1987); (14 pages) | Cited 8 times

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Steady state responses to the sinusoidal modulation of the amplitude or frequency of a tone were recorded from the human scalp. For both amplitude modulation (AM) and frequency modulation (FM), the responses were most consistent at modulation frequencies between 30 and 50 Hz. However, reliable responses could also be recorded at lower frequencies, particularly at 2–5 Hz for AM and at 3–7 Hz for FM. With increasing modulation depth at 40 Hz, both the AM and FM response increased in amplitude, but the AM response tended to saturate at large modulation depths. Neither response showed any significant change in phase with changes in modulation depth. Both responses increased in amplitude and decreased in phase delay with increasing intensity of the carrier tone, the FM reponse showing some saturation of amplitude at high intensities. Both responses could be recorded at modulation depths close to the subjective threshold for detecting the modulation and at intensities close to the subjective threshold for hearing the stimulus. The responses were variable but did not consistently adapt over periods of 10 min. The 40‐Hz AM and FM responses appear to originate in the same generator, this generator being activated by separate auditory systems that detect changes in either amplitude or frequency.
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43.64.Ri Evoked responses to sounds
43.64.Qh Electrophysiology of the auditory central nervous system
43.64.Bt Models and theories of the auditory system

Maximum directivity proof for three‐dimensional arrays

Alan T. Parsons

J. Acoust. Soc. Am. Volume 82, Issue 1, pp. 179-182 (1987); (4 pages)

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A proof is presented for the following theorem: Given all possible three‐dimensional (3‐D) configurations of n omnidirectional acoustic sensors with vanishingly small separations, and given all possible weighting schemes and steer directions, the directivity index achieves an overall maximum value of n2 when the sensors are configured as a linear array steered to end‐fire, it being immaterial whether or not the sensor spacings are equal.
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43.60.Gk Space-time signal processing, other than matched field processing
43.38.Hz Transducer arrays, acoustic interaction effects in arrays

Transient pressure fields of PVDF transducers

D. A. Hutchins, H. D. Mair, and R. G. Taylor

J. Acoust. Soc. Am. Volume 82, Issue 1, pp. 183-192 (1987); (10 pages) | Cited 2 times

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The radiated pressure fields of pulsed polyvinylindene difluoride (PVDF) transducers have been determined experimentally, and compared to theory in three dimensions. The tranducers were in the form of disks, cones, or bowls, excited with a range of known transients in the form of gated sinusoidal voltages. It is demonstrated that good agreement is possible between theory and experiment, and it is shown that more marked interference effects occur as the duration of excitation tone burst is increased. It is also shown that PVDF transducers may be manufactured so as to behave as plane piston radiators.
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43.35.Yb Ultrasonic instrumentation and measurement techniques
43.58.Jq Wave and tone synthesizers
43.38.Fx Piezoelectric and ferroelectric transducers

Surface roughness induced attenuation of reflected and transmitted ultrasonic waves

Peter B. Nagy and Laszlo Adler

J. Acoust. Soc. Am. Volume 82, Issue 1, pp. 193-197 (1987); (5 pages) | Cited 11 times

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The problem of ultrasonic transmission and reflection at a randomly rough interface is considered in connection with ultrasonic NDE of rough surface samples by immersion method. A simple first‐order phase perturbation technique is used to calculate both transmitted and reflected components for comparison with experimental results. The transmitted wave is shown to be attenuated in a similar way to the reflected one, and their attenuation ratio is found to be independent of frequency in the considered cases of slight surface roughness. For instance, the surface roughness induced attenuation of the wave reflected from a water–aluminum interface is about seven times higher than that of the transmitted component. Experimental results are presented to show good agreement with calculated predictions of the suggested simple technique.
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43.35.Zc Use of ultrasonics in nondestructive testing, industrial processes, and industrial products
43.35.Pt Surface waves in solids and liquids
43.30.Hw Rough interface scattering

Theory of three‐dimensional acoustic propagation in a wedgelike ocean with a penetrable bottom

Michael J. Buckingham

J. Acoust. Soc. Am. Volume 82, Issue 1, pp. 198-210 (1987); (13 pages) | Cited 8 times

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A new analytical solution is presented for the three‐dimensional acoustic field due to a monotonic point source in an ocean wedge with a penetrable bottom. The field consists of a sum of normal modes which depend weakly on range (out from the apex) and frequency. The mode coefficients depend strongly on range, on z (cross range parallel to the apex), and on frequency. A dispersion relation is derived which gives the range‐dependent mode shapes. Then a notional ‘‘effective’’ wedge is constructed with perfectly reflecting boundaries whose apex is displaced from that of the penetrable wedge. The offset is such that the range‐independent modes in the effective wedge match the range‐dependent modes in the penetrable wedge. A known solution for the perfect wedge is then modified, by excluding rays which intersect the bottom at greater than the critical grazing angle, to give the spatial and frequency dependence of the mode coefficients in the penetrable wedge. The new solution, which satisfies the Helmholtz equation and the boundary conditions, exhibits prominent 3‐D features uniquely associated with the penetrable bottom. These features conform with ray‐theoretic predictions. Toward the end of the article the transient field in the penetrable wedge due to an impulsive point source is derived by Fourier transforming the cw solution. The Green’s function for the velocity potential is a transient of extended duration which contains evidence of image smearing, a phenomenon due directly to the phase shift experienced by rays undergoing total internal reflection from the penetrable interface.
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43.30.Bp Normal mode propagation of sound in water
43.30.Cq Ray propagation of sound in water

Numerical modeling results for mode propagation in a wedge

F. B. Jensen and C. T. Tindle

J. Acoust. Soc. Am. Volume 82, Issue 1, pp. 211-216 (1987); (6 pages) | Cited 4 times

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A PE (parabolic equation) code is used to study propagation in a shallow water wedge with a penetrable bottom. Particular attention is given to ‘‘wedge modes’’ that have wave fronts that are arcs of circles centered on the wedge apex. For downslope propagation and for upslope propagation before cutoff, the wedge modes propagate independently without coupling. For upslope propagation through cutoff, there is a small amount of coupling to the next lower mode and a trace of coupling to the next higher mode. The wedge modes can be considered the natural modes of the wedge.
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43.30.Bp Normal mode propagation of sound in water

Mode coupling and the environmental sensitivity of shallow‐water propagation loss predictions

Suzanne T. McDaniel and Diana F. McCammon

J. Acoust. Soc. Am. Volume 82, Issue 1, pp. 217-223 (1987); (7 pages) | Cited 4 times

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Variations of seabed parameters, particularly the acoustic compressional velocity relative to that of the water column, have a very strong effect on the predicted magnitude of the propagated acoustic field. In many cases, the sensitivity of the predicted losses to the assumed seabed parameters is sufficiently severe to render the predictions meaningless. In this article, coupled‐mode theory is employed to study how the presence of lateral seabed inhomogeneities affects this sensitivity. The dependence of predicted propagation losses on sediment sound speed is first examined for horizontally stratified sediments; then a rough layered structure of clay–silt interbedded with sand is assumed. With the introduction of rough sub‐bottom layering, coupling occurs between modes, so that the conversion of energy into progressively higher‐order modes, which attenuate rapidly, becomes an important loss mechanism. The extent to which acoustic energy penetrates the seabed and interacts with the sub‐bottom inhomogeneities is governed by the sediment sound speed. Hence, the mode coupling that is induced is simply another loss mechanism dependent on sediment sound speed, leading to an increase in sensitivity to this parameter. Studies to determine the effect of inhomogeneous sediment layering on the transverse horizontal spatial coherence of the propagated field reveal that, even in the presence of mode coupling, the coherence remains high over many acoustic wavelengths, in agreement with measured data trends.
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43.30.Bp Normal mode propagation of sound in water
43.30.Ft Volume scattering
43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics

A postprocessing method for removing phase errors in the parabolic equation

David J. Thomson and David H. Wood

J. Acoust. Soc. Am. Volume 82, Issue 1, pp. 224-232 (1987); (9 pages) | Cited 1 time

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A method is presented for transforming numerical solutions of the standard parabolic equation of ocean acoustics into solutions of the Helmholtz equation. The method is based on an established integral transform [J. A. DeSanto, J. Acoust. Soc. Am. 62, 295–297 (1977)] that is exact for range‐independent media. The Fourier–Bessel transform (with respect to range) of the Helmholtz equation is shown to be related to the Fourier transform of the parabolic equation by means of a nonlinear mapping between horizontal wavenumbers. As a result, fast field program (FFP) techniques can be applied to the Fourier transform of the solution to the standard parabolic equation to obtain an approximate solution to the Helmholtz equation. Several numerical examples are presented to illustrate this postprocessing approach to correcting the phase errors inherent in standard parabolic equation predictions.
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43.30.Bp Normal mode propagation of sound in water
43.30.Cq Ray propagation of sound in water
43.20.Bi Mathematical theory of wave propagation

Bearing determination in a waveguide

Y. Y. Wang, C. S. Clay, and E. C. Shang

J. Acoust. Soc. Am. Volume 82, Issue 1, pp. 233-237 (1987); (5 pages) | Cited 2 times

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Laboratory studies of source bearing determinations were made in an air waveguide having rigid boundaries. The waveguide height was 0.12 m. The signal transmissions were 12‐kHz gated sine waves. Modes 0–8 were possible, however, most of the received signals were in the first four modes. Without mode filtering, theory shows that beamforming in the end fire direction should be poor and it is. This is the first kind of trouble. The analysis shows that beamforming of unfiltered signals also depends on range. As the source changed range at constant bearing (end fire), the apparent direction changed by as much as 25°. This is trouble 2. As expected, beam steering on mode‐filtered signals performed well.
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43.30.Bp Normal mode propagation of sound in water
43.60.Gk Space-time signal processing, other than matched field processing
43.20.Mv Waveguides, wave propagation in tubes and ducts
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