摘要:

In this work, three‐dimensional finite‐element models of the normal and surgically repaired cat middle ear were developed. The normal middle‐ear model was formed by adding explicit representations for the footplate and cochlear load to an existing model of the cat eardrum. The footplate was modeled as a thin plate with a thickened rim. The cochlear load was represented by springs attached along the footplate’s periphery. The model is valid for frequencies below 1 kHz and for physiological sound levels. Eardrum and manubrium displacements, and out‐of‐plane displacements of the footplate’s center, were found to compare well with experimental results. The normal model was modified to simulate the effects of two types of middle‐ear surgery, both of which are used to repair a discontinuous ossicular chain. Bulging of the footplate was found to occur when a prosthesis made direct contact with the footplate. The location of the prosthesis along the manubrium did not affect the motion of the footplate as long as the joints were all rigid. When the joints were flexible, the largest displacements occurred when the prosthesis was positioned near the upper end of the manubrium.

ISSN:0001-4966    

DOI:10.1121/1.416205

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

Spontaneous otoacoustic emissions (SOAEs) and external tones (XTs) were used as primariesf2andf1, respectively (frequency off2≳f1) to create 2f1−f2distortion product otoacoustic emissions (DPOAEs). Amplitude and frequency of the SOAEs, XTs, and DPOAEs were recorded by placing a sensitive microphone in the ear canal and extracted using fast Fourier transform analysis. XTs were presented to ten ears at SOAE/f1ratios between 1.08 and 1.22. XTs were incremented in 5‐dB steps and ranged from levels equal to the initial SOAE amplitudes to levels at which the SOAEs and DPOAEs were suppressed into the noise floor. Results indicated that DPOAE amplitudes and SOAE suppression characteristics were idiosyncratic. Despite the variability, the following trends were noted: (1) at larger frequency ratios, DPOAE generation and SOAE suppression were associated with greater XT levels; (2) DPOAE growth functions were characterized by slopes less than 1 dB/dB, a maximum, rollover and disappearance into the noise floor with increasing XT levels; (3) maximum amplitude DPOAEs were observed at frequencies approximately one‐half octave lower than the SOAE (f2); (4) the presence of DPOAEs was associated with SOAE suppression; (5) the most common SOAE frequency shift, in the presence of XT stimulation, was a shift to a higher frequency.

ISSN:0001-4966    

DOI:10.1121/1.416206

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

This study examined the effect of primary stimulus level on the ability of distortion product otoacoustic emission (DPOAE) measurements to separate normal‐hearing from hearing‐impaired ears. Complete I/O functions were obtained for ninef2frequencies on 210 people approximately evenly divided between normal hearing and hearing impaired. Clinical decision theory was used to assess both DPOAE amplitudes and DPOAE threshold as diagnostic indicators of hearing status. Moderate level primary stimuli elicited responses that separated normal from impaired better than either lower level or higher level stimuli. The two populations were differentiated for all frequencies above 500 Hz by DPOAE amplitude, given primary levels,L1andL2, of 65 and 55 dB SPL. DPOAE threshold performed equally well, but threshold ambiguity in noise and longer testing times make it a less suitable DPOAE measure to use diagnostically.

ISSN:0001-4966    

DOI:10.1121/1.416207

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

Distortion product otoacoustic emission (DPOAE) input/output functions were measured at ninef2frequencies ranging from 500 to 8000 Hz in 210 normal‐hearing and hearing‐impaired subjects. In a companion paper [Stoveretal., J. Acoust. Soc. Am.100, 956–967 (1996)],L1−L2was held constant at 10 dB, andL2was varied from 65 to 10 dB SPL in 5‐dB steps. Based upon analyses using clinical decision theory, it was demonstrated that DPOAE amplitudes for 65/55 dB SPL primaries (L1/L2) and DPOAE thresholds resulted in the greatest separation between normal and impaired ears. In this paper, the data for these two conditions were recast as cumulative distributions, which not only describe the extent of overlap between normal and impaired distributions, but also provide the measured value (i.e., the specific DPOAE amplitude or threshold) for any combination of hit and false alarm rates. From these distributions, confidence limits were constructed for both DPOAE amplitude and threshold to determine the degree of certainty with which any measured response could be assigned to either the normal or impaired population. For these analyses, DPOAE measurements were divided into three categories (a) response properties that would be unlikely to come from normal ears, (b) response properties that would be unlikely to come from impaired ears, and (c) response properties for which hearing status was uncertain. Based upon DPOAE amplitude measurements, the region of uncertainty, defined between the 95 percentile for impaired ears and the 5 percentile for normal ears, was relatively narrow forf2frequencies ranging from 707 to 4000 Hz. For DPOAE thresholds, this region was relatively narrow forf2frequencies ranging from 1414 to 4000 Hz.

ISSN:0001-4966    

DOI:10.1121/1.416208

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

The effects of stimulation rate on the brain‐stem auditory evoked response (BAER) of developing and adult cats were investigated. Age ranged from 10‐post‐natal days to young adults. Clicks were presented at levels of 90 dBpSPL and 20 dB above each animal’s click threshold (20 dB SL). For all animals, a conventional BAER rate series was obtained at rates of 5, 10, 30, 60, and 90 Hz. BAERs were also obtained using pseudorandom pulse sequences called maximum length sequences (MLSs). The minimum time between pulses, the minimum pulse interval (MPI), included 0.5, 1, 2, 4, and 6 ms, which correspond to average rates of 1000, 500, 250, 125, and 83 Hz, respectively. Dependent variables included the latencies of the first four BAER peaks, labeled i through iv. MLS BAERs were indistinguishable from conventional BAERs at all ages studied. In general, for both conventional and MLS BAERs, peak latencies and the i–iv interval increased with increasing stimulus rate. Although absolute peak latencies and the i–iv interval decreased systematically with age, the relative shift in latency and i–iv interval induced by increasing stimulus rate decreased during development. The enhanced sensitivity to stimulus rate observed at younger ages was not the consequence of the threshold improvement that occurs during development since similar observations were made when stimuli were presented at a constant absolute level (90 dBpSPL) or at a constant level above threshold (20 dB SL). In addition, successive BAER peaks exhibited progressively larger latency shifts with increasing stimulus rate at all ages studied. These data suggest that higher stimulus rates produce greater neural adaptation resulting in prolonged BAER peak latencies. Furthermore, the effects of adaptation are cumulative across synapses, and the mechanisms responsible for the acquisition of adult‐like adaptation properties develop during the early post‐natal period in the cat.

ISSN:0001-4966    

DOI:10.1121/1.416209

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

The effects of click rate on brain‐stem auditory evoked response (BAER) peak amplitudes were investigated in adult cats and kittens in four age groups: 10, 15, 20, and 30 post‐natal days. Conventional BAERs were obtained at rates of 5, 10, 30, 60, and 90 Hz. Maximum length sequences (MLSs) were used to obtain responses at rates of 83, 125, 250, 500, and 1000 Hz. For both techniques, clicks were presented at 90 dBpSPL, and at 20 dB above threshold (20 dB SL). BAERs were observed for all age groups, at all click rates. However, not all peaks could be identified in all animals, with peak absence more common for the youngest kittens at the higher rates. BAER waves i through iv decreased in amplitude with increasing click rate for all age groups. In general, the smallest peak amplitudes were observed for the youngest animals (10‐ to 15‐day‐old) studied, while the largest amplitudes were found for the adult, 20‐ or 30‐day‐old animals, regardless of rate. When amplitudes were normalized to eliminate the influences of differences in absolute values due to developmental stage (i.e., made proportional to the amplitude observed at 5 Hz), the younger age groups exhibited enhanced sensitivity to the effects of stimulus rate. However, exceptions to this trend were observed. In general, amplitudes of BAER peaks obtained with the MLS procedure were smaller than those obtained using conventional averaging with a similar average click rate, regardless of age. Finally, the most efficient method for obtaining a response at a criterion signal‐to‐noise ratio was typically by the use of conventional averaging at a rate of 60 or 90 Hz, for all peaks and age groups. Overall, these data suggest that higher stimulus rates produce greater neural adaptation resulting in reduced BAER peak amplitudes. The mechanism responsible for the acquisition of adult‐like adaptation properties appears to develop during the early post‐natal period in the cat.

ISSN:0001-4966    

DOI:10.1121/1.416210

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

A normative study of the cubic distortion product emissions from 104 monaural and binaural chinchillas was undertaken to establish criteria upon which noise exposed animals could be evaluated. From this normative group, 47 randomly selected chinchillas were exposed to various high level (150‐, 155‐, and 160‐dB peak SPL) impulse noises. Auditory evoked potentials and cubic distortion product otoacoustic emissions were measured on each animal pre‐ and post‐exposure and related to the sensory cell populations 30 days post‐exposure. Both group mean and individual animal data indicated that the distortion product emissions were more sensitive, frequency‐specific indices of noise‐induced cochlear effects than pure‐tone threshold measures. This was particularly evident near the threshold for noise‐induced damage to the outer hair cell system.

ISSN:0001-4966    

DOI:10.1121/1.416285

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

Explanations for the phenomenon known as comodulation masking release (CMR) generally assume that temporal envelope information from different peripheral filters is compared, thus entailing multiple envelope representations. Here it is shown that a leaky‐integrator model, yielding a single envelope representation extracted from a broad frequency range, provides an alternative account of CMR. One prediction obtained from model simulations is that adding a single tone to the stimulus will disrupt the CMR effect, leading to an increase in thresholds. Supporting evidence from several experiments shows that the magnitude of CMR is reduced following the addition of a single tone, even when separated from comodulated masking and flanking bands by more than an octave. Whereas these findings are consistent with the leaky‐integrator model, they cannot be easily explained by models which assume multiple envelope representations.

ISSN:0001-4966    

DOI:10.1121/1.416287

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

There is a large deterioration in intensity discrimination performance at medium levels for a 30‐ms sinusoidal pedestal presented 100 ms before or 100 ms after an intense masker [Plack and Viemeister, J. Acoust. Soc. Am.92, 3097–3101 (1992)]. It has also been demonstrated that the loudness of a 30‐ms sinusoidal tone burst, presented 100 ms after a masking tone burst, is enhanced at mid‐levels [Zeng, J. Acoust. Soc. Am.96, 2127–2131 (1994)]. The present experiment measured intensity discrimination and loudness enhancement in both forward and backward masking. A double‐staircase adaptive procedure was used to match the loudness of a 30‐ms, 1‐kHz standard sinusoid presented in quiet to the loudness of a 30‐ms, 1‐kHz sinusoid presented 100 ms after (forward masking) or 100 ms before (backward masking) a 110‐ms, 90‐dB, 1‐kHz masking sinusoid. The mean of the thresholds from the two staircases was used to determine the amount of enhancement, and the difference between the thresholds from the two staircases was used to determine the intensity just noticeable difference (jnd). Four listeners were tested at a range of standard levels between 30 and 90 dB. For all listeners, in both forward and backward masking, the jnd and loudness were greatest at mid‐levels (40–70 dB). For a given listener, there was no substantial difference between the form of the results under forward compared to backward masking, although there was considerable variability in the size of the effects between the individual listeners. Combining all the data, for both forward and backward masking there was a positive correlation between the size of the jnd and the magnitude of the loudness enhancement, although the correlation was only significant in backward masking (p<0.005). Taken with the results of Zeng, these data suggest a link between loudness enhancement and the jnd increase, and a link between the mechanisms underlying the effects of forward and backward masking on intensity discrimination. It is suggested that all these effects may be caused by long‐term loudness integration in the auditory system.

ISSN:0001-4966    

DOI:10.1121/1.416288

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

Three experiments investigated the finding [Placketal., J. Acoust. Soc. Am.97, 1141–1149 (1995)] that intensity discrimination under backward masking can be improved by presenting an additional, ‘‘proximal,’’ tone burst shortly before or after the pedestal. All the stimuli used in the experiments were 30‐ms, 1‐kHz sinusoids. In the first experiment, intensity discrimination was measured for a 50‐dB SPL pedestal presented 100 ms before an 80 dB SPL masker. A proximal tone burst was presented either before or after the pedestal, separated from the pedestal by a brief silent gap. For the conditions in which the proximal burst was before the pedestal, adding a proximal burst with a higher level than the pedestal produced an improvement in intensity discrimination. The most effective level of the proximal burst increased as the gap was increased. For the conditions in which the proximal burst was after the pedestal, two listeners showed an improvement when the proximal burst was lower in level than the pedestal, and one listener showed an improvement when the proximal burst was higher in level than the pedestal. In a second experiment, detection threshold measurements showed that good performance was not dependent on the proximal burst masking the pedestal in one of the two observation intervals. The final experiment used a selective training procedure to demonstrate that listeners were basing performance on two conflicting strategies, namely, to pick the interval that sounded as if it had three tone bursts in it when the proximal level was higher than the pedestal level, and to pick the interval that sounded as if it had two tone bursts in it when the proximal level was lower than the pedestal level. A model of temporal resolution is presented that can explain certain aspects of the results in terms of the detection of ‘‘bumps’’ in the temporal excitation patterns produced by the stimuli. In conditions of backward masking, these relative features seem to provide a superior cue for intensity discrimination than absolute intensity, which is actively rejected as a cue.

ISSN:0001-4966    

DOI:10.1121/1.416289

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP