摘要:

Basilar membrane (BM) velocity responses were measured in the presence of olivocochlear bundle (OCB) stimulation. Frequency threshold tuning curves (FTCs) were derived from tone-evoked input–output (I/O) functions. Efferent nerve activation produced decreases in velocity amplitude for frequencies around best frequency (BF) at low stimulus levels with little or no effect for stimuli well below the BF. A level-dependent efferent reduction/enhancement of BM velocity was found for certain stimulus frequencies above the BF. Efferent activation either had no effect or caused small reductions in the velocity response produced by low level sound, whereas, at higher stimulus levels, efferent activationincreasedthe velocity response. The derived FTCs, therefore, showed criterion-dependent changes with efferent activation. For low BM criterion velocities, FTCs showed the classic desensitization of the tip region without a shift of BF. Some BM velocity criterion values showed FTCs with an expanded high-frequency response area, also without a shift of BF. The results suggest that the effect of OCB activation changes the gain of the voltage-dependent outer hair cell motility such that BM velocity response near BF is decreased while increasing the response for tones well above BF.

ISSN:0001-4966    

DOI:10.1121/1.421008

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

This study investigated the frequency specificity of the auditory brainstem (ABR) and middle latency (MLR) responses to 500- and 2000-Hz brief tones using high-pass noise masking. Stimuli were linear- (2-1-2 cycles) and exact-Blackman- (5 cycles) gated tones presented at 80 dB peak-to-peak equivalent (ppe) SPL. Cochlear contributions to ABR waveV-V′and MLR wave Na-Pa were assessed by the effects of high-pass noise masking on response amplitudes and latencies. The high-pass noise results demonstrate that the ABR and the MLR to the 80 dB ppe SPL brief tones show good frequency and place specificity. Changes in ABR or MLR amplitude and latency with high-pass noise masking did not occur as the masker cutoff was decreased from 2 to 3 octaves above the stimulus nominal frequency until it was within one-half octave of this frequency, below which amplitudes rapidly decreased (500- and 2000-Hz tones) and latencies increased (500-Hz tones). No significant differences existed in the frequency specificity of the ABR versus MLR, or in these evoked potentials to exact-Blackman- versus linear-gated tones.

ISSN:0001-4966    

DOI:10.1121/1.420148

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

This study investigated the frequency specificity of the auditory brainstem (ABR) and middle latency (MLR) responses to 500- and 2000-Hz brief tones using narrow-band derived response analyses of the responses recorded in high-pass masking noise [Oates and Stapells, J. Acoust. Soc. Am.102, 3597–3608 (1997)]. Stimuli were linear- and exact-Blackman-gated tones presented at 80 dB ppe SPI. Cochlear contributions to ABR waveV-V′and MLR wave Na-Pa were assessed by response amplitude profiles as a function of derived band center frequency. The largest amplitudes of waves V and Na-Pa occurred in the 500- and 707-Hz derived bands in response to the exact-Blackman- and linear-gated 500-Hz tones. The peak in the response amplitude profiles for wave V to both 2000-Hz stimuli was seen in the 2000-Hz derived band. For wave Na-Pa, the maxima in the amplitude profiles occurred in the 2000- and 1410-Hz derived bands for the exact-Blackman- and linear-gated tones. Smaller cochlear contributions to the ABR/MLR were also present at 0.5–1 octave above and below the nominal stimulus frequencies. The ABR/MLR to 500- and 2000-Hz 80 dB ppe SPL tones thus shows good frequency specificity, with no significant differences in the frequency specificity of: (1) ABR versus MLR; (2) these evoked potentials to 500- versus 2000-Hz tones; and (3) responses to exact-Blackman- versus linear-gated tones.

ISSN:0001-4966    

DOI:10.1121/1.420400

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Carboplatin produces a selective loss of inner hair cells in chinchilla, substantially reducing the amplitude of the compound action potential. A key question that arises from these experiments is: What effect does a reduction in IHC-eighth-nerve fiber input have on the central auditory nervous system? This investigation evaluated the inferior colliculus potential (ICP) in chinchillas treated with carboplatin. The left ear was surgically destroyed and a recording electrode was placed in the left inferior colliculus. Following thirteen days of recovery time, the ICP was recorded in the awake animal. Click level was varied from 10–20 to 80 dB pSPL. Click rate was varied from 10 to 1000 Hz using both conventional averaging and a cross-correlation procedure. Broadband masking noise was varied from 30 to 70 dB SPL with click level held constant at 80 dB pSPL. The dependent variables were the positive peak latency and peak-to-following trough amplitude of the evoked potential. Following baseline studies, the animals were administered carboplatin (50 mg/kg IP) and retested two weeks later. Prior to carboplatin administration, there was an increase in ICP latency and a decrease in ICP amplitude with decreasing stimulus level, increasing rate and increasing noise level. Mean ICP threshold was 30 dB pSPL. Following carboplatin administration, there was little change in threshold or peak latencies. In contrast, the amplitude of the ICP was reduced on average by one-third, although this effect varied considerably across animals. The magnitude of this amplitude decrement was not strongly dependent on click level, click rate, or the level of background noise.

ISSN:0001-4966    

DOI:10.1121/1.420149

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

A classical problem in auditory theory is the relation between the loudnessL(I)and the intensity just-noticeable difference (JND)ΔI(I).The intensity JND is frequently expressed in terms of the Weber fraction defined byJ(I)≡ΔI/Ibecause it is anticipated that this ratio should be a constant (i.e., Weber’s law). Unfortunately,J(I)is not a constant for the most elementary case of the pure tone JND. Furthermore it remains unexplained why Weber’s law holds for wide-band stimuli. We explore this problem and related issues. The loudness and the intensity JND are defined in terms of the first and second moments of a proposed randomdecision variablecalled thesingle-trial loudnessL̃(I),namely the loudness isL(I)≡EL̃(I),while the variance of the single trial loudness isσL2≡E(L̃−L)2.The JND is given by the signal detection assumptionΔL=d′σL,where we define the loudness JNDΔL(I)as the change in loudness corresponding toΔI(I).Inspired by Hellman and Hellman’s recent theory [J. Acoust. Soc. Am.87, 1255–1271 (1990)], we compare the Riesz [Phys. Rev.31, 867–875 (1928)]ΔI(I)data to the Fletcher and Munson [J. Acoust. Soc. Am.5, 82–108 (1933)] loudness growth data. We then make the same comparison for Miller’s [J. Acoust. Soc. Am.19, 609–619 (1947)] wideband noise JND and loudness match data. Based on this comparison, we show empirically thatΔL(L)∝L1/p,wherep=2below≈5sones and is 1 above. SinceΔL(I)is proportional toσL,whenp=2the statistics of the single-trial loudnessL̃are Poisson-like, namelyσL2∝L.This is consistent with the idea that the pure tone loudness code is based a neural discharge rate (not the auditory nerve). Furthermore, whenp=1(above about 5 sones), the internal loudness signal-to-noise ratio is constant. It is concluded that Ekman’s law(ΔL/Lis constant) is true, rather than Weber’s law, in this loudness range. One of the main contributions of this paper is its attempt to integrate Fletcher’s neural excitation pattern model of loudness and signal detection theory.

ISSN:0001-4966    

DOI:10.1121/1.420150

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

The principles of theoretical acoustics were applied to approximately reconstruct the sound pressure waveform at the ear as would be generated by an idealized struck-clamped bar. The result is an inharmonic sum of damped sinusoids whose individual acoustic parameters (frequency, intensity, and decay modulus) are, for a fixed geometry and fixed driving force, uniquely determined by the material composition of the bar. In the standard 2IFC procedure, listeners were asked to discriminate changes in material composition based on their perception of the acoustic waveform. Listener strategies for discriminating such changes were estimated by perturbing slightly the individual acoustic parameters from trial to trial and computing correlations with the listener’s response [cf. R. A. Lutfi and E. Oh, J. Acoust. Soc. Am.95, 2963(A) (1994)]. In general, the correlations reveal that listeners fail to make optimal use of the information in the acoustic waveform by tending to give undue weight, for a given material change, to changes in component frequency. In some case, the accompanying reduction in performance efficiency amounted to 80%.

ISSN:0001-4966    

DOI:10.1121/1.420151

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

This study examined how effectively information about amplitude modulation (AM) on two carriers is combined, and whether the detection of AM depends on the relative phase of the AM across carriers. Psychometric functions were measured for detecting 5-Hz sinusoidal AM of carriers with frequencies 1100 and 1925 Hz, with a mean level 65 dB SPL for each carrier. The carriers had a duration of 400 ms with 50-ms raised-cosine ramps on either side of this. A single cycle of 5-Hz sinusoidal AM (200 ms in duration) was imposed on the temporal center of the stimulus, with 100-ms steady-state fringes before and after the modulation. The modulators for the two carriers were either in phase or in antiphase. The modulation of each carrier was equally detectable, as determined in a preliminary experiment. A continuous pink noise background was used to mask the outputs of auditory filters tuned between the two carrier frequencies. There was no effect of relative modulator phase. However, performance was consistently better than predicted from the assumption that information about AM from the two carriers is processed independently and combined optimally. The results are discussed in terms of (1) predictions using Dau’s “modulation filter bank model” [T. Dau et al., inPsychoacoustics, Speech and Hearing Aids, edited by B. Kollmeier (World Scientific, Singapore, 1996), pp. 45–48], and (2) the fact that relative modulator phase does have an effect on the detection offrequencymodulation on two carriers, as found by Furukawa and Moore [J. Acoust. Soc. Am.100, 2299–2311 (1996)].

ISSN:0001-4966    

DOI:10.1121/1.420152

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

The present research employed an operant conditioning procedure typically used with infants to test noise masking of pure tones and tonal complexes in adults and in 7-month-old infants. Adults and infants were presented with either pure tones of 160 and 200 Hz or harmonic tonal complexes with pitches equivalent to 160 and 200 Hz. The tonal complexes did not contain energy at the fundamental frequency. After learning these tasks, subjects in the tonal complex group categorized spectrally varying tonal complexes according to the pitch of the missing fundamental. Stimuli were subsequently presented in combination with either a low- or a high-frequency noise. Both age groups successfully discriminated pure tones when combined with a high-frequency noise but not when combined with a low-frequency noise in the same frequency range as the pure tone. Infants, like adults, successfully categorized harmonic tonal complexes based on the pitch of the missing fundamental when those stimuli were combined with a low-frequency noise in the range of the missing fundamental but not when combined with a high-frequency noise which covered the frequency range of the harmonics themselves. These results suggest that infants rely primarily on a central process and not peripherally generated combination tones to hear the pitch of the missing fundamental.

ISSN:0001-4966    

DOI:10.1121/1.420153

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

This study investigated the relationship between electrode discrimination and speech recognition in 11 postlingually deafened adult cochlear implant subjects who were implanted with the Nucleus/Cochlear Corporation multichannel device. The discriminability of each electrode included in a subject’s clinical map was measured using adaptive and fixed-level discrimination tasks. Considerable variability in electrode discriminability was observed across subjects. Two subjects could discriminate all electrodes, and discrimination performance by the remaining nine subjects varied from near perfect to very poor. In these nine subjects, the results obtained from the discrimination tasks were used to create a map that contained only discriminable electrodes, and subjects’ performance on speech recognition tasks using this experimental map was measured. Four different speech recognition tests were administered: a nine-choice closed-set medial vowel recognition task, a 14-choice closed-set medial consonant recognition task, the NU6 Monosyllabic Words Test [T. W. Tillman and T. Carhart, Tech. Rep. No. SAM-TR-66-55, USAF School of Aerospace Medicine, Brooks Air Force Base, Texas (1966)] scored for both words and phonemes correct, and the Central Institute for the Deaf (CID) Everyday Sentences test [H. Davis and S. R. Silverman,Hearing and Deafness(Holt, Rinehart, and Winston, New York, 1978)]. Seven of the nine subjects tested with the experimental map showed significant improvement on at least one speech recognition measure, even though the experimental map contained fewer electrodes than the original map. Three subjects’ scores improved significantly on the CID Everyday Sentences test, three subjects’ scores improved significantly on the NU6 Monosyllabic Words test, and five subjects’ scores improved significantly on the NU6 Monosyllabic Words test scored for phonemes correct. None of the subjects’ scores improved significantly on either the vowel or consonant tests. No significant correlation was observed between electrode discrimination ability and speech recognition scores or between electrode discrimination ability and improvement in speech recognition scores when programmed with the experimental map. The results of this study suggest that electrode discrimination tasks may be used to improve speech recognition of some cochlear implant subjects, and that each electrode site does not necessarily provide perceptually distinct information.

ISSN:0001-4966    

DOI:10.1121/1.420401

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Experiments have been carried out to investigate the information transfer available via a single vibrator on the fingertip. In a first experiment, for stimuli with durations 80 to 320 ms, discrimination of a one-octave step change in frequency at the halfway point was investigated. Results were similar for three stimulus types—sinewave, monophasic pulse and tetraphasic pulse—suggesting temporal cues are more important than spectral cues in this task. In a second experiment, subjects were required to perceive changes in a sequence of stimulus elements. A presentation rate of 6.25 elements s−1was found to give better results than a rate of 12.5 elements s−1. In the former case, the potential information transfer per element was estimated to be approximately 1.0 bits, corresponding to an information transfer rate of around 6 bits s−1. Implications for the design of a tactile aid to lipreading are discussed.

ISSN:0001-4966    

DOI:10.1121/1.420154

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP