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At least 145 records · Page 8Linked to original sources
PubMed1997

Evidence of peripheral hearing asymmetry in humans: clinical implications.

Auditory system hemispheric asymmetry in language processing is well-established, and there are many indications of lateralization as of the peripheral auditory system i.e., as of the cochlea. The left ear is more susceptible to noise damage; tinnitus is more predominant there, while spontaneous otoacoustic emissions (SOAEs) are more often found in the right ear. The present study addressed the following two questions: Does this right-ear SOAE prevalence exist as early as preterm birth? Is there any functional asymmetry in the medial olivo-cochlear (MOC) efferent system, known to modulate outer hair cell contractions? The study involved 483 preterm neonates (gestional age: 24-37 weeks) and 70 right-handed adults (age: 18-31 years). In each ear, SOAEs and evoked otoacoustic emissions (EOAEs) were recorded and analysed, and, for the adults, functional MOC system assessment was made. Results showed SOAEs and EOAE amplitude to be right-predominant and in adults a right MOC functional predominance. These results indicate peripheral auditory system lateralisation, and an early origin thereof. The MOC system being thought to play a protective role, its physiological lateralisation may be relevant to the left prevalence of tinnitus and of auditory fatigue.

Acoustic Stimulation↗
PubMed1997

Comparison of preoperative electrostimulation data using an ear-canal electrode and a promontory needle electrode.

OBJECTIVE: To compare the electrical stimulation results of the ear-canal electrode with those of a promontory needle. PATIENTS AND METHODS: In thirty-three adult patients, the ear-canal electrode test was compared with the needle electrode promontory test with respect to sound perception, rhythm detection, frequency, and disturbing side effects. RESULTS: The ear-canal electrode test, in comparison with the needle electrode promontory test, resulted in vibrotactile sensation in addition to auditory sensation in some patients, less auditory fatigue, higher threshold levels, and lower discomfort levels. CONCLUSION: Reliable assessment of deafness in children requires, in addition to electrical stimulation, determination of the electrical evoked auditory brainstem response with the patient under anesthesia.

Adult↗
PubMedDate not supplied

Experimental exposure to impulse noise in the especially pathogenic impact frequency range.

The pathogenicity of impulse-induced noise depends not only on its intensity, but also on the repetition rate of the individual sound impacts. The reason is the effect exercised by the acoustical reflex. Its protective function is said by some experts to last for only little more than 2 seconds. For this reason, two groups of young persons were exposed to noise impacts whose repetition rates were 2 and 3 seconds, thus falling within the period of time in question. The resulting auditory fatigue (TTS) is analysed. The results of the measurements suggest that the activity of the acoustical reflex lasts less than 2 seconds under these test conditions.

Acoustic Stimulation↗
PubMed1986

Differential susceptibility to noise-induced permanent threshold shift between albino and pigmented guinea pigs.

Evidence that reduced levels of cochlear melanin are associated with increased auditory sensitivity, increased levels of auditory fatigue and an increased susceptibility to noise-induced hearing loss led us to investigate the effects of noise exposure on the cochlear microphonic (CM) in albino and pigmented English shorthair guinea pigs. CMs were recorded from the round window prior to and at 90 min and 7 days after exposure to 45 min of 126 dB noise. Thresholds for the first detectable elicitation of the CM for four pure tones were determined and the output voltage of each cochlea was measured in 10 dB steps through intensity levels which produced a maximum voltage amplitude in the CM and voltage rollover. This analysis demonstrated that: albino guinea pigs displayed significantly lower auditory thresholds than did pigmented animals before exposure to noise; thresholds were elevated to comparable levels in both groups 90 min after noise exposure; pigmented guinea pigs showed a reliable recovery in CM thresholds 7 days after exposure to noise while thresholds in the albinos remained elevated to the same degree at both 90 min and 7 days after noise; 90 min after noise exposure, the maximum voltage output of albino cochleas was significantly less than that recorded from the cochleas of the pigmented guinea pigs. These results demonstrate that albino guinea pigs are more susceptible to the ototoxic effects of high intensity noise than pigmented guinea pigs. Converging evidence indicates that some aspects of cochlear function involve melanin pigment and that its absence may produce auditory abnormalities. Reduced melanin pigmentation may also contribute to such phenomena as noise-induced threshold shifts and individual differences in noise-induced hearing loss.

Albinism↗
PubMed1981

[Binaural disparity for tone thresholds at 4 and 6 kHz: demonstration by iterative audiometry and application of an acoustical stress].

In 24 subjects hearing levels at 4 and 6 kHz were measured 28 times. The ear providing the largest number of best scores manifests itself mainly during recovery of auditory fatigue. The degree with which it manifests itself differs strongly from one frequency to the other. In at least 40% of the cases it is not the same ear. In a majority of cases, it is the right one for both frequencies. On the basis of binomial testing, predominance of either ear at 4 kHz is identified in 12 subjects and at 6 kHz in 6 subjects, predominance at both frequencies being present in 3 of them.

Adult↗
PubMed1994

Sensitivity of distortion-product otoacoustic emissions in humans to tonal over-exposure: time course of recovery and effects of lowering L2.

An important concern of industrial hearing-conservation programs is detecting the onset of noise-induced hearing loss. If it can be shown that otoacoustic emissions are sufficiently sensitive to reliably detect auditory fatigue and the permanent hearing loss that eventually develops, they could become an important part of the hearing-conservation test battery. The present study in humans was designed to examine the influence of overall primary-tone level and the effects of lowering the f2 primary on the sensitivity of distortion-product otoacoustic emissions (DPOAEs) to acoustic overstimulation. One ear from each of 14 subjects with normal hearing was exposed to a 105-dB SPL pure tone at 2.8 kHz for 3 min using a protocol consisting of distinct pre-exposure, exposure, and post-exposure periods. As a quantitative index of the functional status of the outer hair cells, 2f1-f2 DPOAEs were monitored systematically over time using four stimulus-test conditions consisting of either one of two levels of equilevel primary tones, or one of two levels of offset primaries, with L2 set 25 dB lower than L1. The overall finding was that the DPOAE protocol incorporating both the lowest level of stimulation and an f2-primary tone that was 25 dB below the level of the f1 stimulus [i.e., L1 (55 dB SPL) - L2 (30 dB SPL) = 25 dB] was most sensitive to the exposure effects. The results establish that DPOAEs elicited with unequal, in contrast to equal-level primaries, have comparable signal-to-noise ratios, but are considerably more sensitive to reductions in emission levels induced by exposure to short-lasting, moderately intense tones. The recovery of DPOAE amplitudes over the first 15 min post-exposure appeared to be roughly linear in log time and, in many cases, could be closely approximated by fitting a logarithmic curve to the post-exposure data. From these functions, the initial amount of loss (y-intercept) and the slope of recovery were identified as potential measures of vulnerability to acoustic exposure in that these variables appeared to be related to the susceptibility of some of the subjects, who also participated in a subsequent experiment on the behavioral effects of the exposure stimulus. Finally, compared to behaviorally measured temporary threshold shift (TTS), the time course of the recovery for DPOAEs was very similar, suggesting that, with the appropriate parameters, DPOAEs can be as sensitive to TTS as routine pure-tone audiometry.

Acoustic Stimulation↗
PubMed1981

The effects of variable noise level on man with peak levels below 75 dB(A).

To estimate the effect of variable traffic noise levels by field study, six healthy students were exposed to such noise for 8 h in a building beside a highway. TTS increases and blood pressure changes were observed. A summary of the results is as follows: 1. Noise level slightly exceeded 70 dB(A) (Equivalent Sound Level, Leq). The ninety percent range of the changing noise level was within L50 + 10 dB(A). 2. The Temporary Threshold Shift (TTS) induced by variable noise increased slightly in this field experiment. In particular, regression of the logarithm of exposure time (min) to TTS at the "S" ward office, was statistically significant. Some subjects showed a rise of blood pressure due to noise exposure. 4. Even though noise level is below 75 dB(A), 8 h noise exposure induces TTS increase and elevation of blood pressure.

Auditory Fatigue↗
PubMed1986

Binaural beats and frequency-coding.

Binaural beats were studied before and during a situation of temporary threshold shift, and no frequency shift could be found. In contrast, subjective binaural frequency comparison revealed a distinct shift. These findings demonstrate the two known modes of perception.

Audiometry↗
PubMed1980

Effects of temporary thershold shift on combination-tone generation and on two-tone suppression.

Two-tone suppression and combination tone generation (2f1 - f2) are two phenomena that can be described by a single cochlear nonlinearity. Both phenomena are affected by a permanent threshold shift, which supports the idea of a common origin. In the present experiment the effect of a temporary threshold shift (TTS) on both phenomena is investigated. A clear effect of TTS on combination tone level and phase was found, but no effect on two-tone suppression. Limited data and small TTS require caution when the results are interpreted. Tentatively, the results contradict the common-origin concept. The (reversible) effect of TTS on the combination tone demonstrates that the combination tone is not simply due to nonlinear basilar membrane mechanics, but that a sensorineural process is involved.

Auditory Fatigue↗
PubMed1982

Reduced temporary and permanent hearing losses with multiple tone exposures.

Acoustic overstimulation of the guinea pig cochlea with a 16 kHz pure tone induces a loss in threshold sensitivity that can be either temporary or permanent depending on the duration of the trauma. When a second tone of lower frequency (10, 5 or 2 kHz) is presented to the same cochlea simultaneously with the first tone, then the resultant threshold loss produced by the 16 kHz tone is significantly less. This applies to both temporary and permanent threshold losses. The reduced threshold loss disappears as the intensity of the second tone decreases. This type of nonlinear cochlea behaviour is similar to other acoustically evoked nonlinearities generally grouped under the term, two-tone suppression or inhibition. The results disagree with the "equal energy hypothesis' as a method to establish damage risk criteria in noise-induced hearing loss.

Animals↗
PubMed1983

Recovery of eighth nerve action potential thresholds after exposure to short, intense pure tones: similarities with temporary threshold shift.

Exposure of guinea pig cochleas to short (25, 250 and 1000 ms), intense (90 or 100 dB SPL) 10 kHz pure tones reduced cochlear sensitivity to 14 kHz test tones presented at intervals varying from 5 ms to 70 s after the exposure tone. The recovery of cochlear sensitivity, determined as the SPL required to evoke a 20 microV compound action potential (CAP), depended on both the intensity and the duration of the exposure tone and appeared to take place in two or more phases. After a 25 ms, 100 dB SPL exposure, CAP threshold increased by up to 13.5 dB and generally recovered very rapidly (25 ms), although some loss persisted for as long as 400 ms. A similar, but greater and longer, elevation of threshold was seen after long exposure tones. Lower exposure tone intensities (90 dB SPL) produced threshold elevations which generally lasted for only short durations (25-35 ms). The rapid recovery is consistent with the time course of recovery from rapid adaptation, while the slow recovery component is similar to that seen in the cochlea after much longer exposures and may be related to the phenomenon of temporary threshold shift. Long and/or loud exposures also frequently resulted in a third form of threshold elevation, identified in only a few animals, which recovered with a time constant in excess of 25 s. A fourth component occasionally persisted for the duration of the experiment.

Acoustic Stimulation↗
PubMed1983

Crossed cochlear influences on monaural temporary threshold shifts.

Temporary threshold shifts (TTS) of the cochlear action potential in one (ipsilateral) ear, caused by a brief intense pure tone, were reduced either by (1) contralateral acoustic stimulation at the same frequency, or (2) destruction of the contralateral cochlea. The effect of contralateral cochlear destruction persisted, though slightly reduced in effect, after a delay of one hour between the destruction and the ipsilateral exposure. Contralateral acoustic stimulation had no effect after a delay of 10 min. The effect of contralateral cochlear destruction could be blocked by strychnine, a known antagonist of auditory efferent activity. However, contralateral cochlear destruction resulted in none of the effects upon normal ipsilateral thresholds or input-output curves for the action potential classically seen when the efferent pathways are stimulated. The results suggest that the crossed effects reported here are due to a complex interaction between the activity in both cochleas, possibly resulting in a reduction in a central inhibitory influence on an efferent feedback pathway that is then expressed during the ipsilateral exposure.

Acoustic Stimulation↗
PubMed1983

Residual effects in monaural temporary threshold shifts to pure tones.

Temporary threshold shifts (TTS), of the cochlear action potential in the guinea pig, caused by a high frequency exposure tone could be reduced by a prior exposure at the same frequency but lower intensity. The TTS caused by the initial, low intensity exposure tone was allowed to recover to levels where the thresholds were not significantly different from normal thresholds. Re-exposure at the high intensity now resulted in less TTS being recorded, both at the half-octave point and across the range of frequencies affected by the pure tone, when compared to exposure to the high intensity tone without such priming. This protective effect of prior exposure was not affected by intraperitoneal injections of strychnine, distinguishing it from recent reports of protective mechanisms operative during TTS.

Acoustic Stimulation↗
PubMed1985

The influence of moderate-intensity noise on the compound action potential evoked by tone bursts in the guinea pig, Cavia porcellus.

Noise-induced changes in the compound action potential (CAP) evoked by tone bursts in the frequency range 0.5-24 kHz were studied in 15 pigmented guinea pigs by means of chronically implanted electrodes positioned near the round window. The animals were exposed for 120 h to continuous pink noise at the intensities 80, 90 and 100 dB SPL. During the exposure period, all the animals exhibited an exponential rise in CAP threshold, leveling out after 24-72 h (asymptotic threshold shift, ATS). The largest threshold shifts were recorded during exposure to 100 dB SPL, for frequencies in the range 8-12 kHz. In the recovery phase, after the end of noise exposure, the threshold to tones at all frequencies tested fell exponentially, reaching the original level in about 72 h in all cases.

Animals↗
PubMed1987

A comparison of AP and ABR tuning curves in the guinea pig.

AP and ABR tuning curves were measured using a forward masking paradigm in guinea pigs with chronically implanted electrodes. Measurements were made before exposure to wide-band noise and at several intervals after exposure. The noise exposure was sufficient to produce temporary threshold shifts up to 60 dB lasting several days. Results showed similar reductions in Q10, tip-to-tail ratio and slope of simultaneously recorded AP and ABR tuning curves as a function of threshold shift following noise exposure. Tuning curves based on changes in response latency are presented as well as tuning curves based on changes in response amplitude. AP and ABR latency tuning curves showed similar form and changes with hearing loss as amplitude tuning curves. The similarities between AP and ABR tuning characteristics provide evidence that the ABR is sensitive enough to peripheral changes to be useful as a tool to study auditory frequency selectivity. The similarities between amplitude and latency tuning characteristics suggest that information regarding frequency selectivity of the auditory system can be obtained using response latency as well as response amplitude.

Action Potentials↗
PubMed1987

Acoustic overstimulation alters the morphology of the tectorial membrane.

After a permanent threshold shift was induced by exposing guinea pigs to a 1 kHz pure tone at 105 dB(A) for 72 h, light microscopic observations of freshly dissected and stained tectorial membranes showed an increased waviness and clumping of the fibers of the middle zone. Hensen's stripe was not seen as a continuous dense structure running through the middle zone but was at times discontinuous and curved. As measured from cross-sections of the cochlea, the thickness of the tectorial membrane was decreased after acoustic overstimulation. The stereocilia of the inner and outer hair cells lie directly under the middle zone. Visual detection levels of threshold of tectorial membrane movement was determined by stimulating the marginal zone of the tectorial membrane of isolated cochlear coils by an oscillating water jet. After acoustic overstimulation the tectorial membrane became more complaint. The tectorial membrane abnormalities were restricted to the regions of the cochlea that demonstrated a 40-50 dB hearing loss.

Animals↗