摘要:

Recent estimates of auditory‐filter shape are used to derive a simple formula relating the equivalent rectangular bandwidth (ERB) of the auditory filter to center frequency. The value of the auditory‐filter bandwidth continues to decrease as center frequency decreases below 500 Hz. A formula is also given relating ERB‐rate to frequency. Finally, a method is described for calculating excitation patterns from filter shapes.

ISSN:0001-4966    

DOI:10.1121/1.389861

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

Suppression, i.e., the decrease of masked threshold caused by the addition of a second masker M2 to a first masker M1, is measured for the case of simultaneous masking. The magnitude of suppression decreases with increasing test tone duration; pulsed maskers elicit somewhat more suppression than continuous maskers. In comparison to suppression effects obtained in nonsimultaneous masking (post‐masking, pulsation threshold) suppression in simultaneous masking is considerably smaller and was found only at the lower slopes of the two maskers. Suppression in simultaneous masking would not be predicted by those models of suppression which require nonsimultaneous presentation of maskers and test sound.

ISSN:0001-4966    

DOI:10.1121/1.389862

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

The threshold for detection of pure tones in broadband noise was determined for three cats using an auditory reaction time procedure. Critical ratio is defined as the ratio of the signal power at the masked threshold for detection to the spectrum level of the noise. Critical ratios were obtained for 250‐, 500‐Hz, and 1‐, 2‐, 4‐, 8‐, and 16‐kHz tones over a wide range of noise intensities. Results indicate that critical ratios increase with the frequency of the tone stimulus. At frequencies below 4 kHz, critical ratios remain constant at moderate and high noise intensities. For frequencies above 4 kHz, critical ratios increase as the level of the masking noise is raised from moderate to high levels. The difference between low‐ and high‐frequency behavior of the level dependence of critical ratios is considered in terms of two possible mechanisms: (1) different mechanisms may be involved in the encoding of low‐ and high‐frequency information by the nervous system or (2) the difference in level dependence may be due to attenuation by the action of the middle ear muscles at high sound levels.

ISSN:0001-4966    

DOI:10.1121/1.389863

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

In a series of experiments we investigated the time course of adaptation and recovery of channels in the human auditory system selectively sensitive to frequency and amplitude modulation (FM and AM). We determined the rate of loss of sensitivity to modulation using sinusoidal frequency or amplitude modulation (SFM or SAM) of a 50 dB SL, 500‐Hz pure tone carrier over a 30‐min period. Adaptation stimuli were modulated at ten times the preadaptation modulation detection threshold, as determined immediately before the 30‐min adaptation session. Modulation rates investigated were 2, 4, 8, 16, and 32 Hz. Long exposure to SFM always elevated thresholds for detection of SFM more than this exposure elevated thresholds for detection of SAM. Similarly, adapting to SAM always elevated SAM detection thresholds more than SFM thresholds. Loss of sensitivity during adaptation was relatively slow; asymptotic loss of modulation sensitivity took 20 to 30 min. The recovery of modulation sensitivity after cessation of the modulation component of the adapting stimulus was determined in a second experiment. Recovery was found to be rapid; most of the recovery occurred within the first 60 sec. Our evidence suggests that there exist two types of modulation‐sensitive channels in the human auditory system—one selectively sensitive to amplitude modulation and the other to frequency modulation. They appear to have similar time courses for adaptation and for recovery.

ISSN:0001-4966    

DOI:10.1121/1.389864

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

Speech perception by subjects with sensorineural hearing impairment was studied using various types of short‐term (syllabic) amplitude compression. Average speech level was approximately constant. In quiet, a single‐channel wideband compression (WBC) with compression ratio equal to 10, attack time 10 ms and release time 90 ms produced significantly higher scores than a three‐channel multiband compression (MBC) or no compression when a nonsense syllable test (City University of New York) was used. The scores under MBC, WBC, or no compression were not significantly different when the modified rhyme test (MRT) was used. But when overshoots caused by compression were clipped, the MRT scores improved significantly. The influence of MBC on reverberant speech and of WBC on noisy speech were tested with the MRT. Reverberation reduced the scores, and this reduction was the same with compression as without. Noise added to speech before compression also reduced the scores, but the reduction was larger with compression than without. When noise was added after compression, an improvement was observed when WBC had a compression ratio of about 5, attack time 1 ms, and release time 30 ms. Other compression modes (e.g., with high‐frequency pre‐emphasis) did not show an improvement. The results indicate that WBC with a compression ratio around 5, attack time shorter than 3 ms, and release time between 30 and 90 ms can be beneficial if signal‐to‐noise ratio is large, or, if in a noisy or reverberant environment, the effects of noise or reverberation are eliminated by using listening systems.

ISSN:0001-4966    

DOI:10.1121/1.389865

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

We have developed a method for measuring current density within the fluid spaces of the cochlea and report the existence of stimulus evoked radial currents in scala tympani of the guinea pig cochlea. The spatial distribution of electrical potentials in scala tympani was measured along a radial path parallel to the basilar membrane. Click evoked potentials were recorded at successive points separated by a fixed increment as the electrode was either advanced from the spiral ligament or withdrawn from a position near the modiolus. Potential differences were found to exist between recording points and gradients were calculated from the evoked potential measurements. Evoked potential gradients are observed at the same position along the path of the electrode both on advancing and on withdrawing the electrode. The largest potential gradients are located beneath the organ of Corti. Condensation and rarefaction clicks produce radial currents in opposite directions at a given location along the electrode’s path. The magnitude and spatial distribution of radial currents is a function of stimulus intensity. Potential gradients of small magnitude are observed at locations other than below the organ of Corti in some penetrations. Control experiments suggest the smaller gradients are artifactual and may result from displacement of the spiral ligament by the recording electrode. The locations, magnitude, and direction of intracochlear ionic flow relate directly to the mechano‐electrical transduction process in the organ of Corti.

ISSN:0001-4966    

DOI:10.1121/1.389866

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

Two‐tone ‘‘synchrony suppression’’ was studied in responses of single auditory nerve fibers recorded from anesthetized cats. Suppression thresholds for suppressor tones set to a fiber’s characteristic frequency (CF) were approximately equal to discharge rate thresholds for CF tones. Suppression thresholds above and below CF were usually lower than the corresponding discharge rate thresholds. However, at all frequencies studied (including CF), suppression thresholds were higher than the corresponding thresholds for discharge synchronization. Across fibers, rates of suppression growth for suppressors at CF were greatest in low‐CF fibers and least in high‐CF fibers, and there was a systematic decrease in suppression growth rate at CF as CF increased. Within fibers, rates of suppression growth above CF were typically less than at CF, and slopes were monotonically decreasing functions of frequency. Within‐fiber rates of suppression growth below CF were variable, but they usually were greater than rates of growth at CF. Iso‐suppression contours (frequencies and intensities producing criterion amounts of suppression) indicated that tones near CF are the most potent suppressors at near‐threshold intensities, and that the frequency producing the most suppression usually shifts downward as the amount of suppression increases. These data support the notion that synchrony suppression arises primarily as a passive consequence of hair cell activation.

ISSN:0001-4966    

DOI:10.1121/1.389867

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

This paper presents a detailed investigation of the properties of a general class of least‐mean‐square‐fit (LMSF) smoothers in the presence of a white or colored input sequence. The results of the investigation show that the LMSF can be described as a low‐pass filter whose frequency response characteristics can be calculated exactly. A particularly useful result derived from the frequency response characteristics is the LMSF equivalent bandwidth. It was shown that knowledge of LMSF bandwidth, plus knowledge of the input bandwidth, provides the second‐order statistical description of the LMSF output noise process. Results of the analysis are verified by extensive computer simulation.

ISSN:0001-4966    

DOI:10.1121/1.389868

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

Acoustic pressure fields measured by an observer when the source or observer or both are moving is a nonstationary random process even if the source generates a random process which is stationary in the reference frame of the source. The causes of nonstationarity are classified as being due to wave expansion, directivity, and Doppler shift. This paper is concerned with developing two‐dimensional (frequency–time) spectral descriptions for the processes by constraining the processes to fit within the framework of the ‘‘evolutionary spectral density.’’ Earlier literature has described how evolutionary spectra may be estimated from single sample realizations. Spectral representation forms for free‐field acoustic processes produced by moving monopole and dipole excitations are derived from the fundamental wave equations.

ISSN:0001-4966    

DOI:10.1121/1.389869

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

A new technique is described for image formation using a circular array of transducer elements in which each element acts as both a transmitter and receiver. By processing the amplitude and phase measurements acquired in such a system in a particular way, it is shown that it is possible to approach the performance of a transmit–receivefilledcircular aperture of the same dimension. The technique combines a synthetic aperture scheme with an earlier approach for array pattern synthesis ( J2synthesis). The proposed technique does not require spatial incoherence of reflections from the object plane, which was a severe limitation in earlier use ofJ2synthesis. The effect of array sampling with a finite number of transducer elements is also examined.

ISSN:0001-4966    

DOI:10.1121/1.389870

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP