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PubMed1979

Aberrant tonotopic organization in the inner ear damaged by kanamycin.

Spiral ganglion cell recordings were obtained from normal and kanamycin-damaged guinea pig cochleas. Results show that kanamycin poisoning, which causes loss of outer hair cells, leads to a loss of sharp, sensitive tuning and, in addition, a shift to lower frequencies in the tuning curves from a damaged region. The normal tonoptic pattern of organization is therefore greatly disrupted in the damaged cochleas.

Animals↗
PubMed1980

Response properties of spiral ganglion neurons in cochleas damaged by direct mechanical trauma.

Electrical activity of single neurons in the spiral ganglion of the guinea pig cochlea was correlated with receptor hair cell damage produced by local mechanical lesions of the organ of Corti. Damage to or loss of hair cells was assessed using scanning electronmicroscopy. Principal finds were (1) neurons emanating from damaged regions showed changes in their tuning curves such as loss of sensitivity, broadening of tuning curves; (2) in some cases, the loss of sharp tuning tip resulted in an apparent shift of the tuning curve to lower frequencies; and (3) apparently pure outer hair cell lesions, of limited spatial extent, could result in the same effects as mixed inner and outer hair cell lesions.

Animals↗
PubMed1982

Changes in bone conduction thresholds with vibrator contact area.

An experimental bone conduction vibrator was used to measure force and acceleration directly at the point of contact, the subject's forehead. Force and acceleration at threshold were measured for six subjects over a frequency range of 250 to 6000 Hz and over a contact area range of five to one. These measurements suggest that for any test subject, the variation in force of threshold with contact area is much smaller than the corresponding variation in acceleration at threshold.

Audiology↗
PubMed1983

Gap detection as a function of frequency, bandwidth, and level.

The threshold for detection of a temporal gap in a noiseband was measured. A notched noise masker was used to restrict listening to a limited spectral region. Threshold was measured as a function of center frequency, bandwidth, and level. For a signal bandwidth of one-half the center frequency, the gap threshold decreased from 22.5 ms for a center frequency of 0.2 kHz to 3.2 ms at 8.0 kHz: a wideband condition provided an estimate of 2.3 ms, a value in agreement with previously published estimates. Bandwidth manipulation showed that the variation with frequency was not due to changes in absolute bandwidth alone. The effect of changes in level was determined at three frequencies, 0.4, 1.0, and 6.5 kHz, using a signal bandwidth of half the center frequency. At all frequencies gap threshold decreased as the signal spectrum level was raised from 10 to 25 dB, but a further increase to 40 dB showed no additional improvement. At frequencies up to about 1.0 kHz, the variation of gap threshold with frequency matches well the reciprocal of the bandwidth of the auditory filter, as determined from masking experiments using a notched-noise masker. This suggests that the temporal response of the auditory filter may limit gap detection at low frequencies.

Auditory Perception↗
PubMed1984

Interrelation of different oto-acoustic emissions.

Amplitude and phase of the sound pressure measured in the closed ear canal during stimulation with pure tones have been monitored as a function of frequency for subjects with and without measurable spontaneous emissions. The frequency spacing between neighboring maxima of the evoked emissions is closely related to that found between neighboring spontaneous emissions. Similar data are found with delayed evoked emissions. All three catagories , spontaneous, delayed, and synchronous evoked emissions are closely related to each other and to the fine structure of threshold in quiet.

Acoustics↗
PubMed1987

Attenuation and protection provided by ossicular removal.

Behavioral studies of hearing loss produced by exposure to ototraumatic agents in experimental animals, combined with the anatomical evaluation of end-organ pathology, have provided useful information about the relation between dysfunction and pathology. However, in order to attribute a given hearing loss to some pattern of cochlear damage, it is necessary to test each ear independently. The objective of the present study was to evaluate attenuation measured behaviorally and protection to the cochlea provided by removal of the malleus and incus in noise-exposed chinchillas. Results from one behaviorally trained chinchilla with ossicular removal indicated a conductive hearing loss that varied from 41 dB at 0.125 kHz to 81 dB at 4.8 kHz and averaged 60 dB. Counts of missing sensory cells in ears of seven chinchillas with unilateral ossicular removal and exposure to noise (octave band centered at 0.5 kHz, 95 dB SPL, for durations up to 216 days, or centered at 4.0 kHz, 108 dB SPL, for 1.75 h) showed no more cell loss on the protected side than in age-matched control ears. From these data it is concluded that ossicular removal provides enough attenuation to protect the chinchilla cochlea from damage during these noise exposures, and that it will insure monaural responses behaviorally as long as the hearing loss in the test ear does not exceed that in the ear with ossicular removal by approximately 50 dB at any frequency.

Animals↗
PubMed1988

Discrimination of interaural differences of level as a function of frequency.

Discrimination of interaural differences of level (IDLs) was measured for pure tones as a function of frequency and as a function of the interaural difference of phase or level of a standard. Varying the interaural difference of the standard was assumed to change the lateral position of its intracranial image. Threshold IDLs were approximately constant over a frequency range from 200-5000 Hz, except in a region near 1000 Hz where they were slightly elevated. Thresholds increased as the value of the standard interaural differences of phase or level increased, implying that interaural resolution declines as the lateral image moves away from midline. The results are generally consistent with the predictions of current models of lateralization, but additions to these models are required in order for them to account for the slight frequency dependence of threshold IDLs.

Auditory Perception↗
PubMed1989

Hazard from weapons impulses: histological and electrophysiological evidence.

Current methods of rating the hazard of weapons impulses for the ear have recently been challenged by electrophysiological data from experiments with animal ears which indicate that the hazard from low-frequency impulses is much lower than the hazard from higher frequency impulses (Dancer et al., 1981; Price, 1986b). To supplement these data, histological data are reported here for 51 cats that were exposed on one occasion to either rifle or howitzer impulses at peak pressures from 145 to 155 dB or 153 to 166 dB, respectively. Histological procedures (scanning electron and light microscopy) were carried out over 2 months after the exposure and after electrophysiological measures had been made. For both types of impulse the losses tended to be in the middle of the cochlea in focused lesions, even though the spectral peaks of the acoustic stimuli had been at about 80 Hz (howitzer) and 1000 Hz (rifle). Outer hair cells were more susceptible than the inner hair cells and interindividual differences in effects were large. Furthermore, the two impulse sources were equally hazardous when the peak pressure of the rifle impulse was lower than the peak pressure of the howitzer impulse by about 9 dB. In terms of A-weighted energy, the exposures were equally hazardous when the rifle exposure contained about 35 times less energy than the howitzer exposure. The histological data are thus consistent with the electrophysiological data, which indicate that present standards for impulse noise exposure may overrate the hazard of low-frequency impulses relative to impulses in the midrange.

Animals↗
PubMed1990

A comparison of maximum length and Legendre sequences for the derivation of brain-stem auditory-evoked responses at rapid rates of stimulation.

Experiments were performed in which brain-stem auditory-evoked responses (BAERs) were elicited by two types of pseudorandom pulse trains: maximum length sequences (MLS) and Legendre sequences (LGS). In experiment 1, each pulse sequence was presented at 50 dB nHL with minimum pulse intervals varying from 1 to 10 ms. Wave V latency increased and wave V amplitude decreased with decreasing minimum pulse intervals, with no significant effect of the type of sequence (MLS vs LGS), and no significant interaction between sequence and minimum pulse interval in terms of wave V amplitude or latency. In a second experiment, the minimum pulse interval was held constant at 4 ms, while MLS and LGS levels were varied from 20 to 60 dB nHL. With increasing click intensity, there is a decrease in wave V latency and an increase in wave V amplitude. There was no significant effect of type of sequence (LGS vs MLS) or interaction between type of sequence and stimulus intensity for wave V amplitude or latency. Despite the obvious violation of the assumptions (linearity and stationarity) underlying the application of maximum length sequence analysis and Legendre sequence analysis, both techniques produced reliable responses remarkably similar in morphology to evoked responses obtained by conventional averaging. The results of these experiments support the possibility that analysis methods based on pseudorandom pulse sequences may prove more efficient in data collection and provide a more thorough description of the electrophysiologic behavior of the auditory system compared to conventional averaging.

Adult↗
PubMed1990

Brain-stem auditory-evoked responses elicited by maximum length sequences: effect of simultaneous masking noise.

The effects of masking noise on wave V of the brain-stem auditory-evoked response (BAER) obtained to pseudorandom pulse sequences are evaluated in two experiments. In the first experiment, the level of broadband noise was covaried with minimum pulse interval (rate) using maximum length sequence analysis (MLSA). Both increasing noise level and decreasing minimum pulse interval decrease wave V amplitude and increase wave V latency. A nonadditivity of rate and noise level was observed such that, at the shortest interpulse intervals, simultaneous background noise produced virtually no latency change and minimal amplitude change, for the noise levels tested. In a second experiment, high-pass masking was performed to assess the feasibility of derived-band techniques using maximum length sequence analysis (MLSA) and to compare the frequency regions responsible for the BAER using MLSA versus conventional averaging. Results of experiment 2 showed that reliable responses across high-pass masker cutoff frequency could be obtained in normal-hearing listeners. The frequency specificity of the MLSA-based responses was nearly identical to that obtained by conventional averaging, although both amplitude and latency of wave V were affected by the high-pass masker cutoff and minimum pulse interval values. These studies suggest that the neuronal populations and frequency regions responsible for the BAER are virtually the same for MLSA and conventional averaging.

Adult↗
PubMed1991

The structural and functional consequences of acoustic injury in the cochlea and peripheral auditory system: a five year update.

This presentation considers important developments and new trends related to acoustic injury in the peripheral auditory system reported during the past 5 years. The discussion begins with the effect overstimulation has on the "active" cochlear process, and the associated loss in receptive field (tuning curve) selectivity. Exposure to intense sound also changes the structure and function of the tectorial membrane, sensory hair bundles, tip links, and intracellular organelles. All of these injuries may change the way in which energy is delivered to the transduction channels of the hair cell. Important new evidence describing the quantitative relation between hair cell loss and permanent hearing loss is reviewed, and the possibility that specific exposure conditions cause unique lesions to the inner or outer hair cells is explored. Finally, the importance of hair cell regeneration in the chick cochlea, changes in the CNS following acoustic injury, and the cochlear vascular system are considered.

Animals↗
PubMed1993

Analysis of transient-evoked otoacoustic emissions in normal-hearing and hearing-impaired ears.

Transient-evoked otoacoustic emissions (TEOAEs) were measured in 113 normal-hearing and hearing-impaired ears to examine repeatability within a test session, which TEOAE parameter (level, TEOAE level-to-noise or reproducibility) best identified hearing loss and if the TEOAE separated into frequency-specific bands identified hearing loss in a corresponding frequency region. TEOAEs and stimulus levels were found to be very repeatable. For broadband TEOAEs, TEOAE level, TEOAE-to-noise, and % reproducibility were found to identify hearing loss equally well, based on measurement of the area underlying relative operator characteristic curves. Analysis for frequency-specific bands showed that separation of normal-hearing and hearing-impaired ears depended on frequency, with best identification at 2000 and 4000 Hz, identification at 1000 Hz slightly worse, and virtually no separation between normal-hearing and hearing-impaired ears at 500 Hz. Again, all three parameters were essentially equal in identifying hearing loss. Subjective evaluations of presence or absence of TEOAEs was highly correlated between two judges, with good agreement for TEOAEs at 1000, 2000, and 4000 Hz. The findings from this study suggest that TEOAEs will be valuable for clinical use because of their repeatability and identification of hearing-impaired ears.

Acoustic Stimulation↗