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Results for “Auditory Threshold”

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At least 397 records · Page 22Linked to original sources

PubMed2000

The effect of nitrous oxide on hearing.

There is a belief that the administration of nitrous oxide (N2O) increases hearing acuity. This increase can be interpreted as hearing low intensity sounds more loudly. This study examined auditory threshold levels, acoustic impedance, acoustic perception, memory, and discrimination to determine if hearing was altered by end-tidal 10% or 20% nitrous oxide. Subjects also qualitatively interpreted three intensity levels using a subjective intensity test. Observations were made in the breathing mediums of room air in the control stages (Stages 1 and 4), compared to N2O and supplemental oxygen (Stages 2 and 3), in 16 human subjects in a quiet room. Breathing end-tidal 10% and 20% N2O significantly increased middle ear pressure, and produced a significant effect on the subjective interpretation of a sound's intensity. There was no significant effect on auditory threshold at a range of frequencies. It appears that 10% or 20% N2O inhalation does not lead to the commonly held view of increased hearing acuity as measured in terms of auditory threshold. Rather, at these levels of N2O inhalation, subjects experience a state similar to a pre-sleep stage, whereby the hearing diminishes but remains active for loud intensity sounds.

Acoustic Impedance Tests↗

PubMed2001

Ototoxicity in rats exposed to ortho-, meta- and para-xylene vapours for 13 weeks.

Male Sprague-Dawley rats were exposed to ortho-, meta- or para-xylene by inhalation (450, 900 and 1,800 p.p.m., 6 hr/day, 6 days/week for 13 weeks) and sacrificed for morphological investigations 8 weeks after the end of exposure. Brainstem auditory-evoked responses were used to determine auditory thresholds at different frequencies. Among the three isomers studied, only para-xylene produced moderate to severe ototoxicity in rats exposed at 900 and 1,800 p.p.m. Increased auditory thresholds were observed at 2, 4, 8 and 16 kHz in rats exposed to 1800 p.p.m. para-xylene. The auditory threshold shifts (35 to 38 dB) did not reverse after 8 weeks of recovery Moderate and severe losses of outer hair cells of the organ of Corti occurred in animals exposed to 900 and 1800 p.p.m. para-xylene respectively. Thus, the no observed effect level of para-xylene was 450 p.p.m. based on the loss of outer hair cells observed by light and electron microscopy.

Administration, Inhalation↗

PubMed2002

Confirming pure-tone thresholds by auditory brainstem response in the geriatric population.

BACKGROUND: The aged people seeking otological consultation tend to increase for the purpose of applying for hearing disability certificate. When the subjective pure-tone thresholds (PTTs) are unreliable due to patient incooporation, the objective click auditory brainstem response (ABR) is used to confirm the hearing thresholds. In this study, we assess the accuracy of ABR thresholds in the aged and determine the "ABR confirmation criteria" for normal hearing and hearing handicap. METHODS: This is a prospective study. ABR thresholds were compared with pure-tone thresholds (PTTs) in 100 ears of 50 subjects over 60 years of age using kappa measure of agreement. Based on receiver operating characteristic (ROC) curve and positive likelihood ratio (LR), the most appropriate "ABR confirmation criteria" for normal hearing and hearing handicap were determined. RESULTS: According to kappa statistics, the agreement between ABR thresholds and PTTs is better in the 2- to 4-kHz region. For normal hearing, the agreement is best when confirming the average PTTs of 2, 3 and 4 kHz by the ABR threshold of 25 dB nHL (K = 0.53, p < 0.001). For hearing handicap, the agreement is best when confirming the PTTs of 3 kHz by the ABR threshold of 55 dB nHL (K = 0.60, p < 0.001). Based on ROC curve and positive LR, the ABR accuracy, for normal hearing, is excellent at a cutoff of 30 dB nHL compared with the average PTT of 2, 3 and 4 kHz. For hearing handicap, the ABR accuracy is best in excess of 55 dB nHL compared with the PTT at 3 kHz. CONCLUSIONS: We conclude that ABR is a useful diagnostic tool to confirm the validity of pure-tone audiogram for presbycusis.

Aged↗

PubMed2005

Are hearing sensitivities of freshwater fish adapted to the ambient noise in their habitats?

Several groups of fishes, among them two thirds of all freshwater fishes, have developed hearing specializations that enhance auditory sensitivity and broaden frequency ranges compared with hearing non-specialists (generalists), which lack such adaptations. It has been speculated that the enhanced sensitivities of these so-called hearing specialists have evolved in quiet habitats such as lakes, backwaters of rivers, slowly flowing streams or the deep sea. To test this hypothesis, noise levels and frequency spectra of four different freshwater habitats near Vienna, Austria (Danube River, Triesting stream, Lake Neusiedl, backwaters of the Danube River), were recorded and played back to native fish species while simultaneously measuring their auditory thresholds using the auditory evoked potential (AEP) recording technique. As a representative of hearing specialists, we chose the common carp (Cyprinus carpio, Cyprinidae) and for the hearing generalists the European perch (Perca fluviatilis, Percidae). Data show that the carp's hearing is only moderately masked by the quiet habitat noise level of standing waters (mean threshold shift 9 dB) but is heavily affected by stream and river noise by up to 49 dB in its best hearing range (0.5-1.0 kHz). In contrast, the perch's hearing thresholds were only slightly affected (mean up to 12 dB, at 0.1 kHz) by the highest noise levels presented. Our results indicate that hearing abilities of specialists such as carp are well adapted to the lowest noise levels encountered in freshwater habitats and that their hearing is considerably masked in some parts of their distribution range. Hearing in non-specialists such as perch, on the other hand, is only slightly or not at all impaired in all habitats.

Acoustic Stimulation↗

PubMed2005

Estimating audiometric thresholds using auditory steady-state responses.

Human auditory steady-state responses (ASSRs) were recorded using stimulus rates of 78-95 Hz in normal young subjects, in elderly subjects with relatively normal hearing, and in elderly subjects with sensorineural hearing impairment. Amplitude-intensity functions calculated relative to actual sensory thresholds (sensation level or SL) showed that amplitudes increased as stimulus intensity increased. In the hearing-impaired subjects this increase was more rapid at intensities just above threshold ("electrophysiological recruitment") than at higher intensities where the increase was similar to that seen in normal subjects. The thresholds in dB SL for recognizing an ASSR and the intersubject variability of these thresholds decreased with increasing recording time and were lower in the hearing impaired compared to the normal subjects. After 9.8 minutes of recording, the average ASSR thresholds (and standard deviations) were 12.6 +/- 8.7 in the normal subjects, 12.4 +/- 11.9 dB in the normal elderly, and 3.6 +/- 13.5 dB SL in the hearing-impaired subjects.

Adult↗

PubMed1998

Objective evaluation of aided thresholds using auditory steady-state responses.

Auditory steady-state responses to amplitude-modulated tones with modulation frequencies between 80 and 105 Hz can be recorded when multiple stimuli are presented simultaneously through a soundfield speaker and amplified using a hearing aid. Responses were recorded at carrier frequencies of 500, 1000, 2000, and 4000 Hz in a group of 35 hearing-impaired children using hearing aids. The physiologic responses were recorded at intensities close to the behavioral thresholds for sounds in the aided condition, with average differences between the physiologic and behavioral thresholds of 17, 13, 13, and 16 dB for carrier frequencies 500, 1000, 2000, and 4000 Hz. The technique shows great promise as a way to assess aided thresholds objectively in subjects who cannot reliably respond on behavioral testing.

Audiometry, Pure-Tone↗

PubMed1988

Masked thresholds of auditory midbrain neurons in the frog Rana ridibunda.

Single-unit recordings from neurons in the torus semicircularis of Rana ridibunda were analyzed to determine the degree to which these neurons can detect acoustic stimuli superimposed on continuous, broad-band noise. In the first series of trials the stimuli were tone pulses 25 ms long, 5 dB above threshold, and at the characteristic frequency of the neuron. Most cells responded to the stimulus for signal-to-noise ratios of 25-35 dB (tone intensity minus spectral noise density); the lowest values were about 20 dB. The same signal-to-noise ratio was obtained with tones 20 dB above threshold. In the second series, conspecific mating calls at an intensity of 60 dB were tested. Here the signal-to-noise ratio (peak intensity of the call minus noise level) was usually 45-60 dB, in 5 of 27 cells it was 40 dB. Increasing the call intensity to 80 dB raised the SNR by an average of 6 dB. Noise-tolerant units more commonly gave synchronous responses to the pulse groups in the call, and are better tuned to its frequency range, than noise-sensitive units.

Animal Communication↗

PubMed1989

Psychological modulation of auditory responses.

In a study of the cyberphysiology (self-regulation) of auditory response, the effects of imagery and suggestion on auditory thresholds were examined in naive subjects (Ss). After a hypnosis-like induction, the Ss, who were not aware of the purpose of the study, were asked to generate and maintain a specific set of images before, during, and after which their auditory thresholds were tested. The Ss were not informed of the purpose of the imagery or audiograms. Following the imagery, which represented cooling and vasoconstriction in the cochlea, audiograms revealed a temporary auditory threshold shift (TTS) in the experimental group only. This TTS response pattern was similar to that produced by exposure to loud noise. Information carried in the image is suggested as the basis for the observed auditory changes. Although a hypnosis-like induction was employed, the Ss' level of hypnotizability did not appear to be related to the findings.

Adult↗

PubMed2004

Continuous versus pulsed tones in audiometry.

The purpose of this study was to compare auditory thresholds obtained for continuous and pulsed tones in listeners with normal hearing. Auditory thresholds, test-retest reliability, false-positive responses, and listener preference were compared for both signals. Hearing thresholds and test-retest reliability were comparable for the 2 signals, and there were no significant differences in the number of false positives or the number of presentations required to reach threshold. Listener preference, however, indicated that pulsed tones were preferred over continuous tones by 67% of the listeners when listening to low-level or high-frequency tones. These findings, coupled with previous reports demonstrating the benefits of using automatically pulsed tones in threshold assessment for listeners with tinnitus, support the general use of pulsed tones in clinical audiometry.

Acoustic Stimulation↗

PubMed1990

Age-related changes in auditory potentials of Mongolian gerbil.

The Mongolian gerbil is being evaluated as an animal model of age-related hearing loss (presbyacusis). Part of this evaluation involves estimating auditory thresholds from evoked potentials arising from the auditory nerve and brainstem. The gerbils are born and reared in an environment where the ambient noise level is less than 40 dBA. Some animals are followed longitudinally (8, 19, 23.5 and 36 months), others are studied at 6-8 months (controls), or at 36 months (cross-sectional). Physiological responses are obtained with the animals anesthetized with ketamine and xylazine and transdermal electrodes attached to the head. Auditory signals are tone pips with center frequencies from 1 to 16 kHz in octave steps. Signal levels are varied from 10 to 80 dB SPL in 10 dB steps. For animals (N = 48) in the age range of 6-8 months, mean auditory thresholds were about 20 dB SPL between 2.0 and 8.0 kHz, 25 dB at 16 kHz and 30 dB at 1.0 kHz. By age 22-24 months (N = 15) thresholds had increased by about 10 dB at nearly all frequencies. By age 36 months (N = 37 ears, 32 animals) threshold increases were about 30-35 dB at 8 and 16 kHz, were 25 dB at 4 kHz and 2 kHz, and were 19 dB at 1 kHz. These hearing losses in 36-month gerbil are qualitatively similar to human data for 60-65-year-old males and 70-year-old females. Individual differences in hearing loss were large with the range exceeding 65 dB. While some animals (26/37) had a high-frequency sloping loss, others (11/37) had a bimodal audiometric shape where the hearing loss was smallest at 4 kHz and increased by at least 10 dB at adjacent frequencies.

Aged↗

PubMed2000

Predicting exposure conditions that facilitate the potentiation of noise-induced hearing loss by carbon monoxide.

Hearing loss is the most common occupational disease in the United States, with noise serving as the presumed causative agent in most instances. This investigation characterizes the exposure conditions that facilitate the potentiation of noise-induced hearing loss (NIHL) by carbon monoxide (CO). Auditory function was compared in rats exposed 4 weeks earlier to noise alone, CO alone, combined exposure, and air in the exposure chamber. This interval between exposure and auditory threshold assessment was selected to permit recovery of temporary threshold shifts. The compound action potential (CAP) threshold evoked by pure tone stimuli was used as a measure of auditory sensitivity. The no adverse effect level (NOAEL) with respect to potentiation of NIHL was found to be 300 ppm CO. Potentiation of NIHL by CO increases linearly as CO concentration increases between 500 -1500 ppm. Benchmark dose software (version 1. 1B) published by the U.S. EPA National Center for Environmental Assessment was employed to determine a benchmark concentration of CO that produced either a 5-dB potentiation of NIHL or an increase in auditory threshold equivalent to 10% of the effect of noise alone. The lower bound for these benchmark concentrations were 320 and 194 ppm CO, respectively. Unlike CO dose, the relationship between noise severity and potentiation of NIHL by CO shows a nonlinear relationship. The greatest potentiation was observed at moderate noise exposures (100 dB, 2-h, octave band-limited noise, or OBN) that produce limited permanent threshold shifts. Repeated exposures to 95-dB noise for 2-h periods in combination with 1200 ppm CO also yielded potentiation of NIHL, though such effects were not observed following a single combined exposure. These results underscore the potential risk of hearing loss from combined exposure to noise and CO, and the risks associated with repeated exposure.

Action Potentials↗

PubMed1992

Beyond music: auditory temporary threshold shift in rock musicians after a heavy metal concert.

Audiometry was undertaken before and within half an hour following a heavy metal concert to assess evidence of noise damage. Of the four members tested, one member wore an ear defender in his right ear during the period of noise exposure. All unprotected ears showed a temporary threshold shift which was maximum in the lower frequencies. There was some evidence that early noise damage had occurred with a dip at 6 kHz. The role of music as noise and its potential to damage the cochlea are discussed.

Adult↗

PubMed1990

Detection and discrimination thresholds for auditory periodicity.

Complex periodic auditory signals, produced by the Guttman-Julesz procedure of repeating segments of random noise, were employed to address the low region of auditory periodicity. Periodicity detection and discrimination tasks were examined with a common experimental procedure and a common measure of thresholds. Typically, detection and discrimination performance suffer at extremely low periodicities, presumably because of the extremely close spacing of harmonics throughout the auditory spectrum. Interaural phase effects are extremely weak for these signals, being largely confined to threshold-detection tasks. Despite qualitative phenomenological differences for different periodicity regions, detection and discrimination functions show no sharp discontinuities over a wide range of periodicities.

Adult↗

PubMed1985

The effects of phencyclidine and ketamine on sensory thresholds and reaction times in the baboon.

Adult male baboons were trained on a reaction time procedure, and absolute thresholds and reaction times to both a 16.0 kHz pure tone and a white light were obtained. Acute IM injections of phencyclidine (0.0032 to 0.1 mg/kg) or ketamine (0.032 to 3.2 mg/kg) were given at the beginning of 2-hr test sessions. Phencyclidine had no effect on auditory thresholds, visual thresholds, or visual reaction times, but selectively elevated auditory reaction times. Ketamine, on the other hand, elevated auditory thresholds and both auditory and visual reaction times, while having no effect on visual thresholds. Ketamine was also less potent than phencyclidine in elevating auditory reaction times, and recovery from these impairments was evident during the two-hour test sessions for ketamine, but not for phencyclidine.

Animals↗

PubMed1994

Temporal auditory summation in the echolocating bat, Tadarida brasiliensis.

Auditory thresholds improve with increasing signal duration within the maximum integration time of the auditory system, a phenomenon called temporal summation. The temporal summation function is a basic characteristic of particular relevance for bat sonar, as it determines the ability to detect targets with short echolocation calls. Temporal summation was studied in 6 Mexican free-tailed bats (Tadarida brasiliensis) in a forced two-choice behavioural test. Masked auditory thresholds for 40-kHz test tone pulses with durations between 2 ms and 400 ms were determined in broadband noise of two different spectrum levels (-18 dB, +17 dB). At both masker levels, thresholds decreased by considerably more than 10 dB per decade of duration. The time constants of the summation functions, which are a measure of the maximum integration time, shortened significantly with increasing masker level from 62 ms to 14 ms. The steep summation functions are only partly accounted for by spectral splatter. This suggests that the bats are capable of a neural overintegration of sound intensity. Finally, it is shown that such short time constants are typical for echolocating animals, and the implications of the found summation functions for echolocation are considered.

Acoustic Stimulation↗

PubMed1993

The sound world of the child. The relationship between daily activities and hearing acuity.

A group of 50 first, fourth and sixth grade children provided diaries of their activities each hour of the day for 12 consecutive weeks. These activities were correlated with their auditory thresholds assessed at two different times during the behavioral recording period. The results indicated that these schoolchildren experience relatively little noise exposure during their normal daily activities. Further, the incidence of noisy activities was not closely related to hearing thresholds. Other behaviors that are relatively quiet, such as watching television, however, were predictive of higher auditory thresholds.

Audiometry↗

PubMed1994

Inner-ear abnormalities and their functional consequences in Belgian Waterslager canaries (Serinus canarius).

Recent reports of elevated auditory thresholds in canaries of the Belgian Waterslager strain have shown that this strain has an inherited auditory deficit in which absolute auditory thresholds at high frequencies (i.e. above 2.0 kHz) are as much as 40 dB less sensitive than the thresholds of mixed-breed canaries and those of other strains. The measurement of CAP audiograms showed that the hearing deficit is already present at the level of the auditory nerve (Gleich and Dooling, 1992). Here we show gross abnormalities in the anatomy of the basilar papilla of Belgian Waterslager canaries at the level of the hair cell. The extent of these abnormalities was correlated with the amount of hearing deficit as measured behaviorally.

Acoustic Stimulation↗

PubMed1996

Sound-power collection by the auditory periphery of the mongolian gerbil Meriones unguiculatus. II. External-ear radiation impedance and power collection.

Acoustic power flow into the external and middle ear of the gerbil is computed from acoustic measurements and models of the external ear and used to predict the behavioral auditory threshold. The external-ear radiation impedance from the tympanic ring ZE measured in six gerbil ears with a calibrated acoustic source at frequencies from 10 Hz to 18 kHz is mass dominated below about 8 kHz, with a mean mass of 2720 kg/m4. ZE shows resonant behavior near 8 and 14 kHz. The frequency dependence of ZE is similar to that measured in cat, chinchilla, and models of the human external ear, but the mass and the resonant frequencies are higher. The power utilization ratio (PUR) computed from ZE and measurements of the middle-ear input impedance ZT presented previously [Ravicz et al., J. Acoust. Soc. Am. 92, 157-177 (1992)] suggests that appreciable power is transmitted to the middle ear only above 1.5 kHz. Mathematical external-ear models, consisting of tube segments and conical horns that include viscous and thermal losses, were developed from anatomical dimensions to match ZE over the entire frequency range of measurement. The radiation efficiency eta R computed from the models is near unity only above 12 kHz and falls to 10(-5) as frequency decreases to 10 Hz. Predictions of the mean pressure gain from an external diffuse sound field to the tympanic membrane resemble measurements in another gerbilline species. The effective area of the ear in a diffuse sound field at the tympanic membrane EATMDF computed from PUR and eta R approaches the anatomical area of the pinna opening, 71 mm2, above 1.5 kHz and the geometric limit of lambda 2 /4 pi determined by the wavelength lambda above 12 kHz but decreases sharply below 1.5 kHz to 0.002 mm2 at 10 Hz. The diffuse-field sound pressure required to deliver 5 x 10(-17) W to the middle ear between 10 Hz and 18 kHz resembles the behavioral auditory threshold [Ryan, J. Acoust. Soc. Am. 54, 1222-1226 (1976)]. This result supports the idea that the cochlea acts as a power detector at the auditory threshold.

Acoustics↗