摘要:

Three investigations were conducted to determine the application of the articulation index (AI) to the prediction of speech performance of hearing‐impaired subjects as well as of normal‐hearing listeners. Speech performance was measured in quite and in the presence of two interfering signals for items from the Speech Perception in Noise test in which target words are either highly predictable from contextual cues in the sentence or essentially contextually neutral. As expected, transfer functions relating the AI to speech performance were different depending on the type of contextual speech material. The AI transfer function for probability‐high items rises steeply, much as for sentence materials, while the function for probability‐low items rises more slowly, as for monosyllabic words. Different transfer functions were also found for tests conducted in quiet or white noise rather than in a babble background. A majority of the AI predictions for ten individuals with moderate sensorineural loss fell within ±2 standard deviations of normal listener performance for both quiet and babble conditions.

ISSN:0001-4966    

DOI:10.1121/1.394086

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Two experiments are described in which frequency selectivity was estimated, in simultaneous and forward masking, for each ear of subjects with moderate (25–60 dB HL) unilateral cochlear hearing losses. In both experiments, the signal level was fixed for a given ear and type of masking (simultaneous or forward), and the masker level was varied to determine threshold, using an adaptive, two‐alternative forced‐choice procedure. In experiment I, the masker was a noise with a spectral notch centered at the signal frequency (either 1.0 or 1.5 kHz); threshold was determined as a function of notch width. Signal levels were chosen so that the noise level required at threshold for a notch width of zero was similar for the normal and impaired ear of each subject in both simultaneous and forward masking. The function relating threshold to notch width had a steeper slope for the normal ear than for the impaired ear of each subject. For the normal ears, these functions were steeper in forward masking than in simultaneous masking. This difference was interpreted as resulting from suppression. For the impaired ears, significant differences in the same direction were observed for three of the five subjects, but the differences were smaller. In experiment II, psychophysical tuning curves (PTCs) were determined in the presence of a fixed notched noise centered at the signal frequency (1.0 kHz). For the normal ears, the PTCs were sharper in forward masking than in simultaneous masking. For the impaired ears, the PTCs were similar in simultaneous and forward masking, but those in forward masking tended to be sharper at masker frequencies far removed from the signal frequency. Overall, the results suggest that suppression is reduced, but not completely absent in cases of moderate cochlear hearing loss.

ISSN:0001-4966    

DOI:10.1121/1.394087

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Experiments on intensity discrimination determine the size of the smallest detectable increment added to a fixed pedestal. This paper examines the effects of a masker which either precedes the pedestal (forward masking) or is simultaneous with the pedestal. The increment and pedestal were 1‐kHz tones masked in forward masking by pure tones and in simultaneous masking by a broadband noise. Simultaneous masking by the broadband noise eliminates the ‘‘near miss’’ to Weber’s law, and thus degrades intensity discrimination at high pedestal levels. Forward masking by the pure tone also degrades intensity discrimination, which may, in part, be explained by the elimination of the near miss. However, the effect on intensity discrimination in some cases is greater in forward than in simultaneous masking, suggesting that some additional process (e.g., adaptation) is involved.

ISSN:0001-4966    

DOI:10.1121/1.394170

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Masking‐level differences (MLDs) were measured for trains of 2000‐Hz bandpass clicks as a function of the interclick interval (ICI) and the number of clicks in the train. The magnitude of the MLD grew as the number of clicks in the train was increased from 1 to 32. While the MLDs tended to be larger at longer ICIs, the effect was mediated by changes in detectability in the homophasic conditions. For click trains consisting of 4–32 clicks, the improvement in detectability in the antiphasic conditions with increases in the number of clicks appears to be the result of integration of acoustic power, as is the case for the homophasic conditions. The absence of MLDs for short trains of high‐frequency transients remains quite puzzling, since large MLDs are found with single, low‐frequency transients.

ISSN:0001-4966    

DOI:10.1121/1.394171

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Three experiments were performed to obtain vibrotactile sensitivity thresholds from hearing children and adults, and from deaf children. An adaptive two‐interval forced‐choice procedure was used to obtain estimates of the 70.7% point on the psychometric sensitivity curve. When hearing children of 5–6 and 9–10 years of age and adults were tested with sinusoids and haversine pulse stimuli, at 10, 100, 160, and 250 Hz or pps, respectively, only the 10‐Hz stimulus resulted in an age effect. For this stimulus, young children were significantly less sensitive than adults. When sinusoids were again tested at 20, 40, 80, and 160 Hz, a small overall effect of age was observed with a significant effect only at 20 Hz. Two prelingually profoundly deaf children were tested with haversine pulse trains at 10, 50, 100, 160, and 250 pps. Both children were at least as sensitive to the tactile stimulation as were the hearing children and adults. Pulsatile stimulation, compared to sinusoidal stimulation, exhibited relatively flat threshold versus frequency functions. The present results, demonstrating no age effect for pulsatile stimulation and similar performance for deaf and hearing children, suggest that pulsatile stimulation would be appropriate in vibrotactile speech communication aids for the deaf.

ISSN:0001-4966    

DOI:10.1121/1.394172

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

This article is motivated by the current hypothesis [Kimetal.,Psychological,PhysiologicalandBehaviouralStudiesinHearing(Delft U. P., The Netherlands, 1980); Neely, Doctoral dissertation, Washington University, St. Louis, MO (1981); de Boer, J. Acoust. Soc. Am.73, 567–573 (1983a) and73, 574–576 (1983b)] that it is necessary to include active elements in the basilar membrane (BM) impedance in order to explain recent data on the vibration of the BM [Khanna and Leonard, Science215, 305–306 (1982); Sellicketal., J. Acoust. Soc. Am.72, 131–141 (1982); Roblesetal.,PeripheralAuditoryMechanisms(Springer, New York, 1986)]. In order to test this hypothesis, first, a method which is an inversion of the customary description of cochlear mechanics is described. Instead of computing the BM velocity for a given point impedance of the membrane, we show how to compute the impedance function from a given BM velocity pattern in response to a sinusoidal input at the stapes. This method is then used to study the sensitivity of the recovered impedance to perturbations in the velocity pattern. The simulations used show that the real part of the impedance is extremely sensitive to such perturbations. Therefore, measured velocity patterns are unlikely to resolve the issue of whether active elements should be included. Frequency responses measured at a few points on the membrane are even less likely to do so.

ISSN:0001-4966    

DOI:10.1121/1.394460

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

A mathematical model of cochlear processing is developed to account for the nonlinear dependence of frequency selectivity on intensity in inner hair cell and auditory nerve fiber responses. The model describes the transformation from acoustic stimulus to intracellular hair cell potentials in the cochlea. It incorporates a linear formulation of basilar membrane mechanics and subtectorial fluid–cilia displacement coupling, and a simplified description of the inner hair cell nonlinear transduction process. The analysis at this stage is restricted to low‐frequency single tones. The computed responses to single tone inputs exhibit the experimentally observed nonlinear effects of increasing intensity such as the increase in the bandwidth of frequency selectivity and the downward shift of the best frequency. In the model, the first effect is primarily due to the saturating effect of the hair cell nonlinearity. The second results from the combined effects of both the nonlinearity and of the inner hair cell low‐pass transfer function. In contrast to these shifts along the frequency axis, the model does not exhibit intensity dependent shifts of the spatial location along the cochlea of the peak response for a given single tone. The observed shifts therefore do not contradict an intensity invariant tonotopic code.

ISSN:0001-4966    

DOI:10.1121/1.394173

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

A hardware model of the nonlinear preprocessing established in the inner ear consisting of 90 sections corresponding to a frequency range from 900 to 8000 Hz is described. The model is based on assumptions described by Zwicker [Biol. Cybern.35, 243–250 (1979)]: The outer hair cells act as saturating nonlinear mechanical amplifiers which feed back to the vibration of the basilar membrane while only the inner hair cells transfer information towards higher centers. The model shows many effects which correlate very closely to physiological and psychoacoustical counterparts. Quantitative data on the level‐dependence of frequency responses and phase responses as well as an example of suppression are outlined.

ISSN:0001-4966    

DOI:10.1121/1.394175

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Spontaneous, simultaneous evoked as well as delayed evoked emissions are studied in a hardware model of peripheral preprocessing with nonlinear feedback. The results suggest many very close parallels to the data found for otoacoustic emissions in man. From these parallels and the additional data measurable only in the model, it can be concluded that: (a) the cochlea acts in a similar way as established in the model; (b) the three kinds of emissions stem from the same source; (c) the phase response of the cochlea’s hydromechanics is responsible for the frequency distance between neighboring emissions as well as for the additional tips in suppression tuning curves; (d) the long delay of the delayed evoked emissions is due to the many decaying contributions from the places along the basilar membrane which cancel each other in the early part but sum up to the delayed emission in the later part; and (e) the double‐peaked shape of the suppression‐period patterns produced by high‐level, low‐frequency tones reflects the symmetrically shaped saturating nonlinearity of the feedback loops in the model which correspond to the function of the outer hair cells.

ISSN:0001-4966    

DOI:10.1121/1.394176

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

The two nonlinear effects of two‐tone suppression and of (2 f1−f2)‐difference tone creation are measured in a hardware model which consists of 90 sections containing nonlinear feedback loops. The basic data are the level and phase distributions along the 90 sections produced by single tones in the linear passive system which are almost identical to those produced in the nonlinear active system at high levels. Enhancement is created at medium and low input levels resulting in more strongly peaked level‐place patterns. Two‐tone suppression is, therefore, described as a ‘‘de‐enhancement’’ which is produced by the gain reduction in the saturating nonlinearity of the feedback loop in consequence of increasing input levels (that of the suppressor as well!). Characteristics of suppression are given in normalized form. The creation of (2 f1−f2)‐difference tones is based on the same nonlinear effects. In each section, difference‐tone wavelets are created which travel—changing level and phase thereby—to their characteristic place, where they add up to a vector sum corresponding to the audible difference tone. In case of cancellation, the vector sum has to be compensated by an additional tone of the same frequency and amount but opposite phase. Based on this strategy of (2 f1−f2)‐difference tone development, the relevant relations are measured on the model and averaged either in normalized graphs or in equations in order to offer the possibility to simulate the hardware model on the computer. Psychoacoustically measured cancellation data are compared with data measured using the model. The two data sets agree not only in general but also in many details indicating that the model describes cochlear nonlinear preprocessing to a useful approximation.

ISSN:0001-4966    

DOI:10.1121/1.394177

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP