摘要:

Two simple situations are considered ofNmutually coupled oscillators excited at resonance by external random sources. Formulas are derived for oscillator energies that display explicitly the transition from weak to strong coupling between the oscillators. Average oscillator energyE, the average uncoupled oscillator energyEu, and the coupled energyEcare defined. In one situation,E,Eu, andEcare equal; in the second situation,Eis bounded byEuandEc.

ISSN:0001-4966    

DOI:10.1121/1.381815

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Brainstem electrical responses (BSER) to 60‐dB‐SL click in noise high passed at various cutoff frequencies separated by 1/2‐octave steps were recorded in normal‐hearing adult subjects. By applying a derived response technique, narrow‐band contributions to the BSER from specific portions of the basilar membrane were revealed. Latencies and amplitudes of the various waves in the derived BSER were recorded. Results indicate that nearly the whole cochlear partition can contribute to the brainstem response. The shifts in latency of waves I, III, and V and amplitude changes of waves I and III as a function of CF appear to be fully comparable to those of the AP. In contrast, the amplitude behavior of wave V as a function of CF is different from waves I and III depending upon the frequency range. The discrepency in the behavior of wave V with respect to the earlier waves suggests some sort of neural reorganization at the level where wave V is generated. The fact that there are contributions to the brainstem response from apical portions of the cochlea opens the possibility for extending the brainstem technique in assessing the higher cochlear turn function.

ISSN:0001-4966    

DOI:10.1121/1.381816

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Responses to two‐tone stimuli were recorded from auditory‐nerve fibers in anesthetized cats. One tone, the suppressor, was set at a frequency above characteristic frequency and was fixed in intensity. A second tone was set at an excitatory frequency and was varied in intensity. The suppressor tone, when set at a sufficient level, always reduced the response to the excitatory tone by an amount equivalent to a fixed number of decibels, regardless of the excitatory tone’s intensity. Estimates of suppression magnitude were derived from shifts in rate‐intensity function obtained when the suppressor tone was present relative to the functions obtained for the excitatory tone alone. When suppressor‐tone intensity was increased, suppression magnitude likewise increased. When the two tones were increasingly separated in frequency, either by varying the excitor or by varying the suppressor, suppression magnitude decreased monotonically. Suppression behaved in the same manner regardless of whether the suppressor tone was excitatory or nonexcitatory. When frequency separation was small enough and when both tones were above the neuron’s characteristic frequency, responses synchronized to low‐order combination tones could be elicited. These responses usually possessed different rate‐intensity characteristics and resulted in estimates of suppression magnitude which were spuriously low. When frequency separation is normalized with regard to position of traveling wave maxima within the cochlear duct, the magnitude of two‐tone suppression for a given suppressor‐tone intensity is seen to be frequency independent.

ISSN:0001-4966    

DOI:10.1121/1.381817

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Psychophysical experiments show that the pitch of a short sine wave tone depends upon the amplitude envelope of the tone. Subjects find that the pitch of an exponentially decaying tone (1dB/ms) is higher than the pitch of a (20‐ms) rectangularly gated tone of equal frequency. The percentage difference in frequency required to produce equal pitches with the two envelopes depends upon frequencyf0: 2.6% atf0=412 Hz, 1.4% atf0=825 Hz, 1% atf0=1650 Hz, and 0.7% atf0=3300 Hz. The pitch change is insensitive to the relative intensities of the two tones. The spectra of tones with the two different envelopes suggest no obvious explanation for the pitch change. However, the weighted time‐varying spectra for tones with two different envelopes evolve differently with time. Alternatively the pitch change can be derived from a modified version of the auditory phase theory of Huggins.

ISSN:0001-4966    

DOI:10.1121/1.381818

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Over a range of 50 dB, the loudness of a 100‐Hz tone was measured in the presence of a broadband noise with a low‐frequency cutoff at 200 Hz. The noise was varied in intensity along with the tone so that the signal‐to‐noise ratio remained constant at either 0 or −10 dB. Listeners judged the loudness of the tone by loudness matching, magnitude estimation, and magnitude production. The noise markedly decreased the tone’srateof loudness growth but not therangeover which loudness grows. The overall decrease in steepness of the 100‐Hz loudness function was greater than that previously reported at higher frequencies. It is hypothesized that the decrease was greater because the spread of excitation at 100 Hz was more effectively contained than at higher frequencies. Support for this hypothesis is given by measures of intensity discrimination at 100 Hz.

ISSN:0001-4966    

DOI:10.1121/1.381819

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Recent research has demonstrated that the binaural system can utilize ongoing interaural time differences for lateralization at high frequencies as well as at low frequencies. The requirement is that the signal be complex so that the time difference appears as a delay in the envelope of the waveform at one ear. Reported here are several masking experiments that examine detection performance with time‐delayed signals or maskers. In the first experiment, the signal was a 50‐Hz band of noise centered at 4000 Hz that was time delayed by different amounts on different blocks of trials; the masker was a similar band of noise, presented diotically. Large masking‐level differences (MLDs) were obtained for some values of time delay, but the MLDs did not increase monotonically with time delay as they should were envelope time delay the basis for detection performance. Subsequent experiments, in which the masker was time delayed and the signal was a diotic, high‐frequency tone, revealed that detectability follows the autocorrelation function, and that MLDs as large as 24 dB can be obtained at 4000 Hz at time delays corresponding to negative values in the autocorrelation function. Examination of the signal‐plus‐masker waveforms in these conditions reveals that ongoing interaural differences in level and cycle‐by‐cycle time exist in those conditions that yield MLDs. Since the time differences are small by usual standards, the basis for detection performance in these conditions appears to be the ongoing interaural level differences. In a final experiment, lateralization performance was measured for a time‐delayed, complex waveform in the presence of maskers of various intensities. The results show that subjects are able to extract information about the time delay in the envelope even when the signal is added to a masker of equal intensity or greater. Thus, at the small signal‐to‐noise ratios used in our detection experiments, extraction of envelope time information was impossible, but also unnecessary, for detection was accomplished on the basis of another cue—most likely the ongoing interaural level differences.

ISSN:0001-4966    

DOI:10.1121/1.381820

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Random auditory patterns were repliated according to defined rules, converted toauditory pulse trains, and presented to listeners. Three ined: the threshold fraction of repeated elements necessary for a fixed level of discrimination from a nonrepeated pattern; the accuracy of periodicity matching; and periodicity magnitude ratings. A short‐term periodicity analysis over successive replications appears to be more representative of the behavioral measures than a long‐term periodicity analysis. Of the signal measures of periodicity examined, the maximum autocorrelation, irrespective of delay, most closely reflects behavioral measures of periodicity strength.

ISSN:0001-4966    

DOI:10.1121/1.381821

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Groups of six mongolian gerbils were exposed to two‐octave (1414–5656 Hz) band noise for 1 h at 100, 110, and 120 dB SPL. Threshold shift at several frequencies was measured 0.5, 3, 6, and 12 h, and 1–28 days after exposure. Final thresholds were determined at least two months postexposure. Extensive threshold shift was observed in all groups 0.5 h after exposure (TS0.5h). Where threshold shift increased in the initial hours after exposure, such increases were correlated with eventual permanent threshold shift (PTS). Recovery of thresholds from 1–28 days after exposure was approximately exponential, and slowest at the edges of the exposure band. PTS was seen in the 110 and 120 dB SPL groups. With TS0.5hof 50 dB or less, no PTS resulted. With TS0.5habove 50–60 dB, eventual PTS increased linearly with a slope of about 1.25 PTS/TS0.5h. Cochlear damage was evaluated by light microscopy. The relationship between hair cell loss and PTS was consistent with an inner hair cell threshold about 40 dB higher that that of outer hair cells. It is suggested that recovery from noise‐induced threshold shift may involve different mechanisms in the two types of hair cells.

ISSN:0001-4966    

DOI:10.1121/1.381822

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

A new method of studying vertical localization is described whereby the high‐frequency response of the external ear is synthesized by a computer program incorporating two variable latency delay and add processes. The resulting sounds were evaluated by presentation to subjects via headphones which bypass the external ear. Vertical movement of the sound source was perceived when the latency of one echo was changed dynamically between 100 and 300 μs and this effect required the presence of high‐frequency signal components (above around 4 kHz). In further experiments, the variation of perceived elevation with echo delay was measured, and it is shown that the vertical locale of the apparent source is a monotonic function of echo latency in the 160–260 μs region. It is proposed that locale is decoded by a form of spectral pattern recognition, whereby the locale of the source is represented as a peak on an autocorrelation function. The time‐axis values (between 160 and 260 μs) corresponding to these peaks are considered to correspond to vertical locale for elevations between, roughly, 60° above horizontal and 40° below.

ISSN:0001-4966    

DOI:10.1121/1.381823

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

A random‐interval pulse train or wide‐band noise when delayed (τ) and added back to itself (cos+) produces a stimulus with a cosinusoidally varying (or rippled) power spectrum. The spacing between the peaks in the spectrum is equal to the reciprocal of the delay (1/τ). If the stimulus is delayed and added back at 180° phase reversal (cos−), then a cosinusoidally varying power spectrum is generated whose spectral peaks are separated by 1/τ, but whose peaks are displaced by 1/2τ relative to the power spectrum of the cos+ stimulus generated with the same delay, τ. These stimuli yield a pitch, such that the pitch of the cos+ stimulus is equal to approximately 1/τ and the pitches of the cos− stimuli are equal to approximately 0.9/τ and 1.1/τ. These pitch matching results were studied using a variety of matching stimuli and conditions. Following the identification of the pitches, a method of limits and a same–different procedure were used to study the pitch discriminability of both the cos+ and cos− stimuli. Delays (τ) ranging from 1 to 10 ms were studied covering a pitch range of 90–1100 Hz. The pitch discriminations associated with the cos+ and cos− stimuli were essentially the same for both the random‐interval pulse train and the wide‐band stimuli. These pitch‐discrimination results are compared to those associated with a periodic pulse train. The research is also discussed in terms of discriminations of delayed sounds in reverberant environments. These results are consistent with assumptions concerning the autocorrelation of the rippled stimuli within the dominant frequency region for pitch perception.

ISSN:0001-4966    

DOI:10.1121/1.381824

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP