摘要:

An experiment was conducted to measure observers’ ability to detect time‐varying interaural intensity differences (IIDs). In a two‐interval forced‐choice task, observers discriminated a binaural amplitude modulated (AM) noise in which the modulating sinusoid was interaurally in‐phase from the same AM noise in which the modulator was interaurally phase‐reversed. The latter stimulus produces a sinusoidally varying IID whose rate and peak IID depend on the frequency (fm) and depth (m) of modulation. The carrier was a narrow‐band noise, interaurally uncorrelated, centered at 500, 1000, or 4000 Hz. Presentation level was 75 dB SPL; duration was 1.0 s. For a givenfm,mwas varied in an adaptive procedure to estimate the depth required for 71% discriminability (mthr). Three of the four observers displayed ‘‘low‐pass’’ modulation functions: at 500 Hz, asfmincreased from 0–50 Hz,mthrincreased from 0.08 (IID=1.3 dB) to 0.50 (peak IID=9.5 dB). At 1000 and 4000 Hz observers were more sensitive to IID and the functions (mthrvsfm) were flatter than at 500 Hz. Comparison of these data to previously published data indicates that the binaural system can follow fluctuations in IID more efficiently than it can follow fluctuations in interaural time difference, although there are large individual differences in subjects’ capacity to process these two types of binaural cues.

ISSN:0001-4966    

DOI:10.1121/1.391009

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The onset‐time difference ΔTrequired to lateralize a 30‐ms bifrequency tone burst toward the leading ear was measured as a function of the frequency difference ΔFbetween the tone in the left ear and the tone in the right ear. At center frequencies of 0.5 and 4 kHz, four normal listeners tested at 80 and 100 dB SPL had ΔTs that were relatively constant at subcritical ΔFs, but increased at ΔFs wider than a critical band. At 1 kHz, ΔTincreased with ΔFeven at subcritical ΔFs. Ten listeners with cochlear impairments were tested at 100 dB SPL. Seven had normal ΔTs at 4 kHz, despite hearing losses between 50 and 70 dB. At 0.5 and 1 kHz, mildly impaired listeners had nearly normal lateralization functions, whereas more severely impaired listeners had very large ΔTs and no frequency selectivity. These and other findings indicate that listeners even with moderate to severe hearing losses can lateralize normally on the basis of interaural differences in onset envelope, but not on the basis of temporal differences in the fine structure.

ISSN:0001-4966    

DOI:10.1121/1.391010

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Using an adaptive strategy, the effects of mild sensorineural hearing loss and adult listeners’ chronological age on speech recognition in babble were evaluated. The signal‐to‐babble ratio required to achieve 50% recognition was measured for three speech materials presented at soft to loud conversational speech levels. Four groups of subjects were tested: (1) normal‐hearing listeners<44 years of age, (2) subjects65 years old with mild hearing loss and excellent performance in quiet. Groups 1 and 3, and groups 2 and 4 were matched on the basis of pure‐tone thresholds, and thresholds for each of the three speech materials presented in quiet. In addition, groups 1 and 2 were similar in terms of mean age and age range, as were groups 3 and 4. Differences in performance in noise as a function of age were observed for both normal‐hearing and hearing‐impaired listeners despite equivalent performance in quiet. Subjects with mild hearing loss performed significantly worse than their normal‐hearing counterparts. These results and their implications are discussed.

ISSN:0001-4966    

DOI:10.1121/1.391011

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

A set of bandpass filtered, pulsed noise stimuli presented to three normally hearing subjects was found to have psychophysical properties similar to those of a set of pulsed electrical stimuli presented to two cochlear implant patients. Identical procedures were used to compare the performances of the two groups of subjects in the following tasks: (a) pulse rate difference limen measurements, (b) pitch scaling for stimuli differing in pulse rate, (c) pitch scaling and categorization of stimuli differing in filter frequency or electrode position, and (d) similarity judgments of stimuli differing in pulse rate and filter frequency or electrode position. By choosing the parameters of the acoustic stimuli appropriately, a high level of agreement between the two sets of results was achieved. Electrical stimuli on electrodes at different sites in the cochlea were matched with pulsed noise passed through bandpass filters with different center frequencies. Matching was achieved for equal electrical and acoustic pulse rates.

ISSN:0001-4966    

DOI:10.1121/1.391012

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The speech perception of two multiple‐channel cochlear implant patients was compared with that of three normally hearing listeners using an acoustic model of the implant for 22 different speech tests. The tests used included a minimal auditory capabilities battery, both closed‐set and open‐set word and sentence tests, speech tracking and a 12‐consonant confusion study using nonsense syllables. The acoustic model represented electrical current pulses by bursts of noise and the effects of different electrodes were represented by using bandpass filters with different center frequencies. All subjects used a speech processor that coded the fundamental voicing frequency of speech as a pulse rate and the second formant frequency of speech as the electrode position in the cochlea, or the center frequency of the bandpass filter. Very good agreement was found for the two groups of subjects, indicating that the acoustic model is a useful tool for the development and evaluation of alternative cochlear implant speech processing strategies.

ISSN:0001-4966    

DOI:10.1121/1.391104

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Using the cancellation method we investigated the phase relationship as well as the amplitude ratio between impulse signals transmitted simultaneously via both bone and air conduction channels. The psychophysical findings indicated a phase difference corresponding to a time delay of about 0.9 ms by which the air input led the bone input in the case of frontal bone stimulation. Changing the polarity of the bone conduction signal a maximum in the loudness sensation was found just in the same phase difference. The psychophysical findings, predicted mathematically, were verified with brainstem evoked potentials elicited to similar signals. Preliminary results showed that the time lag observed relied on the location of the bone vibrator on the head and furthermore on the frequency used. This suggests different transmissions of vibratory energy reaching the inner ear along the skull.

ISSN:0001-4966    

DOI:10.1121/1.391105

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The responses of cat auditory‐nerve fibers to synthesized consonant–vowel syllables were compared with predictions from linear models based on individual fibers’ threshold tuning curves. Comparisons with the linear predictions provided information about the specific effects of peripheral nonlinearities on the representation of speech sounds. Spectral peaks, such as the formants of vowels, were more prominently represented in synchronized discharge patterns than in the linear predictions. Suppression of responses to other spectral peaks and to stimulus components between spectral peaks accounted for the differences. While profiles of fibers’ synchronized responses were usually dominated by a single formant, predicted linear responses often included broad responses having two or more formants as well as components near the fibers’ characteristic frequencies. In contrast, when no stimulus peak fell within a fiber’s response area, the agreement between the neural response and the linear prediction was quite good. The results suggest that one role for peripheral nonlinearities in the auditory system may be to enhance the neural representation of spectral features such as formants.

ISSN:0001-4966    

DOI:10.1121/1.391106

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

A unified expression for the probability distribution function with quantized state variables for a stochastic noise environmental system is derived in the form of a statistical orthogonal expansion. Next, a new statistical procedure for estimating the precise noise level probability distribution form on the basis of the roughly observed data with a quantized level of a large‐difference interval is proposed as an application of the above unified theory. The validity of the method has been experimentally confirmed by applying it to actual indoor noise data observed in a reverberant room of our university, and to outdoor noise data observed in Hiroshima City itself.

ISSN:0001-4966    

DOI:10.1121/1.391107

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

A Postbeamformer Interference Canceller, PIC, is essentially a single‐channel noise canceller. Two beams are formed; one in the target direction and another in the interference direction. The interference direction beam is processed with a tapped delay filter before being subtracted from the target beam to yield the system output. A detailed analysis of PIC is presented in the paper. The performance which can be achieved with PIC is shown to depend critically on the input signal to interference ratio and the tapped delay line length.

ISSN:0001-4966    

DOI:10.1121/1.391108

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The estimation of the frequency‐wavenumber spectrum of the ambient noise field from data collected by a totally random array is considered. The standard estimator [J. Acoust. Soc. Am.71, 97–99 (1982)], which is a normalized beampower pattern, is shown to be biased for sparse arrays. A modified estimator which removes this bias is introduced and its performance is studied. In particular, precise asymptotic expressions for the bias, variance, and covariance of the estimator are established. The density of the number of sensors per unit volume is allowed to be arbitrary and thus the results hold for sparse arrays as well. An application to a representative planar array is given.

ISSN:0001-4966    

DOI:10.1121/1.391109

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP