摘要:

An adaptive tracking procedure was used to evaluate thresholds at 0.25, 0.715, 2.0, 4.0, and 8.0 kHz in a group of operantly conditioned chinchillas. Signals were synthesized with 10‐ms rise‐fall times and varied in ten duration steps from 15 ms to 1.5 ms. Chinchillas reported the signal by releasing a response key within 2.0 s of its onset. Latency was defined as the interval between the onset of the signal and the key release. Threshold measures showed that the chinchilla integrates energy in the same manner as human listeners, but with a longer time constant. Time constants for chinchillas varied from 400 ms at low frequencies to 100 ms at high frequencies. Measures of response latency as a function of signal duration overlapped for all durations at a given frequency. While long‐duration signals produced a doubling of latency for a 50‐dB reduction of stimulus intensity, short duration signals, as long as they were detected, produced similar latencies as long signals at equivalent SPL's. The implication of this finding will be discussed. [Supported by Grant NS 03856 to the Central Institute for the Deaf.]

ISSN:0001-4966    

DOI:10.1121/1.2017311

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Typically, the threshold of audibility curve is based on threshold determinations at octave intervals and the presumption is generally made that the threshold curve is fairly smooth at frequencies between those at which threshold is measured. In 1975, Thomas [J. Acoust. Soc. Am.57, 526 (1975)] reported findings which indicated that in fact there exist fluctuations in detection threshold of as much as 10 dB which occur with relatively small changes in frequency. The experiments reported here consist of determinations of the detection threshold of sinusoids with no added noise using the 2IFC procedure. The stimulus tone ranged in frequency from 1000 to 2000 Hz. The results indicate that in fact changing the frequency by as little as 30 Hz can cause an increase in the 75% detection level by as much as 12 dB. and further that if the frequency is shifted in the same direction, the detection threshold will decrease. This periodic threshold fluctuation, or the microstructure of the detection threshold curve, will be shown in detail.

ISSN:0001-4966    

DOI:10.1121/1.2017315

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

A lateralization procedure [T. Houtgast, Acustica30, 214‐221 (1974); W. Jesteadt and E. Javel, J. Acoust. Soc. Am.63, S44(A) (1978)] was used to measure the suppression of a monaural 500‐msec, bandpass noise on a 15‐ms tone as a function of the temporal relationship between the suppressor and the tone. Suppression was estimated by presenting the brief tone binaurally and adjusting its level in the contralateral ear in order to produce a centered image. Inferences from pulsation‐threshold and unmasking experiments have led to the belief that suppression must have very short (even instantaneous) rise and decay times, but this simultaneous procedure indicates that the rise and decay have markedly different time courses—at the onset of the suppressor, suppression increases rapidly, but it decays relatively slowly at suppressor offset. Using the same stimuli and subjects, the time course of masking was also measured and the data will be compared with the suppression data. [Work supported by NINCDS.]

ISSN:0001-4966    

DOI:10.1121/1.2017318

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

The only qualitative explanation describing the interaction of combined forward and backward masking involves the temporal positioning of an integrator [C. Robinson and I. Pollack, J. Acoust. Soc. Am.53, 1313–1316 (1973)]. We ran two experiments to test this model. In both experiments, noise masker levels were adjusted so that the maskers were equivalent (i.e., singly, each masker produced the same amount of masking of a click). First suppose, as the model states, that two long maskers, one forward and one backward, position the integrator. If so, then the addition of two more maskers should not affect the signal level by more than 3 dB. In fact, all four maskers result in 12 dB more masking than is produced by the two long maskers only. Second, we compare the masking effect of two forward maskers with that produced by one forward and one backward masker and find the same signal threshold in the presence of either set of equivalent maskers. Since integrator movement seems unlikely in the combined forward masker conditions, the model does not capture the major factor causing the interaction. We introduce an alternative quantitative explanation relating the interaction to the nonlinear coding of intensity. This hypothesis is tested in a third experiment in which we predict the click threshold in the temporal center of a silent interval separating a forward and backward masker. [Work supported by NSF.]

ISSN:0001-4966    

DOI:10.1121/1.2017328

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Thresholds for ten‐tone complexes masked by continuous wide‐band noise were determined for simultaneous and for sequential presentation of the components. Five component durations (10, 20, 50, 100, 200 ms) and four component frequency spacings (3, 6, 50, 200 Hz) centered at 2.5 kHz were used. Thresholds generally increased with increasing frequency spacing. For total durations of 200 ms or less and for a fixed component spacing, signalenergyat threshold was approximately constant regardless of whether the components were presented simultaneously or successively. For durations longer than 200 ms and for small component spacings, signalpowerat threshold was approximately constant, in agreement with the data on temporal integration of pure tones. However, for large component spacings, threshold signalpowercontinued to decrease up to at least 2000 ms. The results suggest that temporal integration precedes combination of information over disparate frequency regions. [Research supported by NINCDS and the Graduate School of the University of Minnesota.]

ISSN:0001-4966    

DOI:10.1121/1.2017331

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Redwing blackbirds, brown‐headed cowbirds, and pigeons were trained using operant conditioning techniques to respond to small increases in the intensity of pulsed tone trains at three frequencies: 0.5, 1.0, and 2.0 kHz. All three species produced similar intensity difference limens (DLs) at the frequencies tested. Intensity DLs decreased as sensation level increased at all three frequencies, with the slopes of these sensation level functions being greatest at 2 kHz. The minimal intensity DLs at 50 dB sensation level were 3.3, 2.7, and 2.8 dB at 0.5, 1.0. and 2.0 kHz, respectively, averaged over the three species. Some subjects who were required to detectdecreasesin intensity produced intensity DLs two to three times larger than the DLs obtained when these subjects were required to detect increases in intensity. Comparative aspects of intensity discrimination will be discussed, and the relations between intensity discrimination and other aspects of hearing will also be considered.

ISSN:0001-4966    

DOI:10.1121/1.2017341

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Under conditions of quiet, the subjective loudness of a pure tone increases with the cube root of the sound pressure for levels less than approximately 70 dB SPL. At this point there is a discontinuity of slope and a second linear process appears. Under conditions of noise, the threshold for the low level process is increased but the function remains linear and the slope is invariant with the level of noise. For the high level process, subjective loudness (S) can be represented by the equation:S = k(Ps0.33 − P00.33) 10−cPu/Ps, wherePa,Pn, andP0are the pressures of the signal, noise, and threshold;kandcare empirical constants. The results which will be reported are consistent with Stevens' power law of sensation; the exponent is invariant under conditions of masking.

ISSN:0001-4966    

DOI:10.1121/1.2017348

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

A U‐shaped array can be made using two surface floats, an underwater anchor, the line of sensors, and a horizontal fish line to maintain array configuration. Conventional beam forming of this array will result in side‐lobe problems. It will be shown how cross‐sensor beamforming can be used to detect weak acoustic targets that have lower levels than the side lobes of stronger targets.

ISSN:0001-4966    

DOI:10.1121/1.2017352

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

It is well known that sonar system performance varies considerably when fixed amount of source energy is divided amongNdiversity signals when the fading is Rayleigh. This paper reviews the Rayleigh results and establishes similar results for chi‐square, Rice, and log‐normal fading. Performance curves are included for both search and communication systems.

ISSN:0001-4966    

DOI:10.1121/1.2017359

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

A state‐wide study was conducted pursuant to development of a Kentucky environmental noise regulation, including assessments of noise and attitudes in 20 cities and impacts of regulation on three mineral processing industries. UrbanLeq(daytime mean = 59.1 dBA, sigma = 7.4 dBA; nighttime 5.5 dBAlower) was sufficient for significant noise annoyance and a small potential for permanent hearing loss, judged by EPA “Levels Document” Criteria. Surface transportation was responsible for 80% of the intrusive events and 67% of the high annoyance ratings. Citizens considered urban noise sufficiently harmful to outdoor activity, sleep, and communication to warrant regulation but preferred local over state or federal control and fines for revenues over taxes. An estimated 39% of the coal, rock, and asphalt plants in the state (responsible for most of the complaints to state officials) would violate a 63 dBAtest limit; engineering control would cost $10.9 million, rising or falling exponentially with the enforcement limit selected. A proposed regulation is now being finalized. [Work supported by the State of Kentucky.]

ISSN:0001-4966    

DOI:10.1121/1.2017364

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP