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Results for “Auditory Threshold”

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PubMed2001

Assessment of dolphin (Tursiops truncatus) auditory sensitivity and hearing loss using jawphones.

Devices known as jawphones have previously been used to measure interaural time and intensity discrimination in dolphins. This study introduces their use for measuring hearing sensitivity in dolphins. Auditory thresholds were measured behaviorally against natural background noise for two bottlenose dolphins (Tursiops truncatus); a 14-year-old female and a 33-year-old male. Stimuli were delivered to each ear independently by placing jawphones directly over the pan bone of the dolphin's lower jaw, the assumed site of best reception. The shape of the female dolphin's auditory functions, including comparison measurements made in the free field, favorably matches that of the accepted standard audiogram for the species. Thresholds previously measured for the male dolphin at 26 years of age indicated a sensitivity difference between the ears of 2-3 dB between 4-10 kHz, which was considered unremarkable at the time. Thresholds for the male dolphin reported in this study suggest a high-frequency loss compared to the standard audiogram. Both of the male's ears have lost sensitivity to frequencies above 55 kHz and the right ear is 16-33 dB less sensitive than the left ear over the 10-40 kHz range, suggesting that males of the species may lose sensitivity as a function of age. The results of this study support the use of jawphones for the measurement of dolphin auditory sensitivity.

Animals↗

PubMed1996

Nymphal development of the auditory system in the praying mantis Hierodula membranacea Burmeister (Dictyoptera, Mantidae).

Like other praying mantises, Hierodula membranacea has a single midline ear on the ventral surface of the metathorax. The ear comprises a deep groove with two tympana forming the walls. A tympanal organ on each side contains 30-40 scolopophorous sensillae with axons that terminate in the metathoracic ganglion in neuropil that does not match the auditory neuropil of other insects. Nymphal development of the mantis ear proceeds in three major stages: 1) The tympanal organ is completely formed with a full complement of sensillae before hatching; 2) the infolding and rotations that form the deep groove are completed primarily over the first half of nymphal development; and 3) over the last five instars (of ten), the tympana thicken and broaden to their adult size and shape, and the impedance-matching tracheal sacs also enlarge and move to become tightly apposed to the inner surfaces of the tympana. Auditory sensitivity gradually increases beginning with the fifth instar and closely parallels tympanum and tracheal sac growth. Late instar nymphs have auditory thresholds of 70-80 dB sound pressure level (SPL). Appropriate connections of afferents to a functional interneuronal system are clearly present by the eighth instar and possibly much earlier. The pattern of auditory system ontogeny in the mantis is similar to that in locusts and in noctuid moths, but it differs from crickets. In evolutionary terms, it is significant that the metathoracic anatomy of newly hatched mantis nymphs matches very closely the anatomy of the homologous regions in adult cockroaches, which are closely related to mantises but are without tympanal hearing, and in mantises that are thought to be primitively deaf.

Acoustic Stimulation↗

PubMedDate not supplied

Response properties in young and old Fischer-344 rat lateral superior olive neurons: a quantitative approach.

Significant age-related functional deficits may result from a selective loss of inhibitory processing in the lateral superior olivary (LSO) nucleus. To test this hypothesis, methods were developed for quantitative comparisons of the excitation evoked by ipsilateral acoustic stimuli and the inhibition evoked by contralateral acoustic stimuli in neurons recorded from this binaural structure. Data were obtained from 103 LSO neurons from 22 young adult (3-6 month) and 70 LSO neurons from 14 old (20-23 month) Fischer-344 (F-344) rats. Age-related increases in the thresholds of auditory brainstem responses as well as in the inhibitory and excitatory responses of LSO neurons were observed. Spike-discharge rates were analyzed using multiple regression analysis for interaural intensity data and by calculating correlation coefficients between excitatory and inhibitory isointensity curves. Most LSO principal cells exhibited ipsilateral excitation and contralateral inhibition of similar strength for similar stimuli. Inhibitory and excitatory response areas of these neurons were similar based on visual inspection and correlation coefficients. No statistically significant age-related changes were observed for (a) rate-level functions generated by ipsilateral or contralateral stimuli; (b) maximal discharge rate; (c) conduction latencies; or (d) measures of binaural function. However, a small percentage of LSO neurons both in young and old rats displayed "unmatched" inhibitory and excitatory response areas. Quantitative methods developed in this study are used to examine age-related changes in binaural function in the inferior colliculus of F-344 rats and in the LSO of the Sprague-Dawley rat. Although no asymmetrical aging changes were observed for the F-344 rat LSO, there appear to be significant differences between the aging auditory system in the F-344 and Sprague-Dawley rats. Age-related changes have been previously described for the F-344 in other brainstem auditory structures.

Acoustic Stimulation↗

PubMedDate not supplied

Comparison of hearing threshold determined by auditory pathway electric responses and by behavioural responses.

In order to evaluate their reliability for determing the hearing threshold, the cochlear microphonic potentials, the auditory nerve and brain stem neural evoked responses as well as the cortical evoked responses were compared with the behavioural hearing thresholds of the same subjects in the same session. The threshold for recording the cochlear microphonic potnetial was found to be appreciably higher than the behavioral threshold. The threshold for recording the auditory nerve and brain stem responses was within a few decibels of the behavioural threshold. The thresold of the cortical evoked response was several decibels higher. It is concluded that (1) the auditory nerve and brain stem neural evoked responses are the best indicators of hearing threshold; (2) the cortical evoked responses are usually comparable, and (3) all types of evoked responses are indispensable aids in the evaluation of hearing and the determination of site of lesion in the auditory system.

Audiometry↗

PubMed2003

Acoustic communication in two freshwater gobies: the relationship between ambient noise, hearing thresholds and sound spectrum.

Two freshwater gobies Padogobius martensii and Gobius nigricans live in shallow (5-70 cm) stony streams, and males of both species produce courtship sounds. A previous study demonstrated high noise levels near waterfalls, a quiet window in the noise around 100 Hz at noisy locations, and extremely short-range propagation of noise and goby signals. To investigate the relationship of this acoustic environment to communication, we determined audiograms for both species and measured parameters of courtship sounds produced in the streams. We also deflated the swimbladder in P. martensii to determine its effect on frequency utilization in sound production and hearing. Both species are maximally sensitive at 100 Hz and produce low-frequency sounds with main energy from 70 to 100-150 Hz. Swimbladder deflation does not affect auditory threshold or dominant frequency of courtship sounds and has no or minor effects on sound amplitude. Therefore, both species utilize frequencies for hearing and sound production that fall within the low-frequency quiet region, and the equivalent relationship between auditory sensitivity and maximum ambient noise levels in both species further suggests that ambient noise shapes hearing sensitivity.

Acoustic Stimulation↗

PubMed1990

Selectively eliminating cochlear microphonic contamination from the frequency-following response.

The frequency-following response (FFR) is the scalp recorded response to low frequency stimuli. As an electrophysiological method for determining auditory threshold, it has application in both clinical and research settings. However, the response is often contaminated with the cochlear microphonic (CM), reflecting the response of outer hair cells, rather than neural generators (i.e., auditory nerve, cochlear nucleus, superior olivary nucleus, inferior colliculus, etc.). The FFR needs to be a purely neural response to establish its clinical and experimental usefulness. The methods applied to date have failed to accomplish this. The present study demonstrates a method of deriving a pure neural response by subtracting a forward masked FFR, which contains only CM, from an unmasked FFR. To confirm that the residual response after forward masking is solely CM, one needs to record two forward masked responses with opposite phase probe stimuli. When the responses are added they will sum to zero only if the residual response with forward masking is pure CM. This study demonstrates that the traditional method for removing CM from FFR, by simple summation of unmasked responses recorded with stimuli of opposite phase, does not accurately reflect the amplitude or frequency of the FFR, while the proposed method provides an accurate assessment of the FFR amplitude free of CM contamination.

Acoustic Stimulation↗

PubMedDate not supplied

Auditory brainstem response threshold estimation: subjective threshold estimation by experienced clinicians in a computer simulation of the clinical test.

Little research has been undertaken into the extent to which auditory brainstem response (ABR) threshold estimation varies between experienced professionals. In this paper, results are presented for 16 professionals who estimated ABR threshold for 12 sets of data in a computer simulation of the clinical test. The design differs from previous research in this area in that subjects had control over the creation of the set of traces from which they would estimate threshold, much as they would in the clinical situation. No agreement for threshold was found for any of the 12 sets of test data across the 16 subjects, and for nine of the sets, the difference between highest and lowest estimated threshold was 40 dB or greater. The maximum difference between highest and lowest estimated threshold was 60 dB. It is argued that the variability is not accounted for by experimental design. The implications for clinical practice are discussed.

Adult↗

PubMed1987

Probe tone thresholds in the auditory nerve measured by two-interval forced-choice procedures.

An important goal of auditory physiology is to relate the coding of signals in the auditory nerve to behavioral sensitivity. A useful step towards that goal is to measure physiological thresholds for the detection of tones in the neural spike train that are comparable to psychophysical thresholds. Detectability depends on the variability as well as the mean value of the response. A two-interval forced-choice task provides a criterion-free measure of detectability. On each trial of our experiments a probe tone was taken to be correctly detected if the number of spikes in response to the tone exceeded the number of spikes in an otherwise identical interval that did not contain the probe tone. (Analysis of the pulse-number distributions also allowed construction of ROC curves directly comparable to psychophysical ROC curves.) The proportion of trials that yielded correct detections was measured as a function of stimulus intensity to form a neurometric function, directly comparable to a psychophysical psychometric function. Threshold was defined as the intensity that produced a given proportion correct. The threshold intensity was also measured by an up-down procedure. Agreement between the two measures of threshold was excellent. Using the up-down procedure we could measure threshold in about 1 min, making it practical to measure the thresholds of a single neuron for many conditions. Comparisons of physiological and psychophysical ROC curves and neurometric and psychometric functions show systematic differences indicating that the animal makes its decisions inefficiently, perhaps by basing its decision on the maximum response among many neurons, rather than just the activity of the single most sensitive neuron.

Acoustic Stimulation↗

PubMed1981

Effects of age on acquisition and maintenance of a location discrimination in rats.

Twelve-and thirty-month old Sprague Dawley rats were trained in an auditory discrimination using a discrete trial procedure with food as the reinforcer. Two thirty-month an two twelve-month animals acquired the discrimination in one trail. The asymptotic level of correct responding was lower for the old animals and this was attributed to changes in auditory threshold with age. The thirty-month animals gave more intertrial interval responses than the twelve-month animals. There was no difference in the average response latency for the two age groups.

Aging↗

PubMed2001

Suppression of the deafness and thyroid dysfunction in Thrb-null mice by an independent mutation in the Thra thyroid hormone receptor alpha gene.

Deletion of thyroid hormone receptor beta (TR beta), a ligand-dependent transcription factor encoded by the Thrb gene, causes deafness and thyroid hyperactivity in Thrb-null (Thrb(tm1/tm1)) mice and in a recessive form of the human syndrome of resistance to thyroid hormone. Here, we have determined that a targeted mutation (Thra(tm2)) in the related Thra gene, encoding thyroid hormone receptor alpha suppresses these phenotypes in mice. Thra encodes a TR alpha 1 receptor which is non-essential for hearing and a TR alpha 2 splice variant of unknown function that neither binds thyroid hormone nor transactivates. The Thra(tm2) mutation deletes TR alpha 2 and concomitantly causes overexpression of TR alpha 1 as a consequence of the exon structure of the gene. Thra(tm2/tm2) mice have normal auditory thresholds indicating that TR alpha 2 is dispensable for hearing, and have only marginally reduced thyroid activity. However, a potent function for the Thra(tm2) allele is revealed upon its introduction into Thrb(tm1/tm1) mice, where it suppresses the auditory and thyroid phenotypes caused by loss of TR beta. These findings reveal a novel modifying function for a Thra allele and suggest that increased expression of TR alpha 1 may substitute for the absence of TR beta. The TR isotypes generated by the distinct Thrb and Thra genes represent a small family of receptors that have diverged to mediate different physiological roles; however, the ability of changes in Thra expression to compensate for loss of Thrb indicates that many functions of these genes remain closely related.

Animals↗

PubMedDate not supplied

[Neurophysiologic tests for the early detection of deafness in children].

Using brainstem auditory evoked potentials and tympanometry the authors have examined 120 children aging from several months to five years and they have found a high percentage of children with hearing impairment with sensorineural deafness. The children had also secretory inflammation of the middle ear. It has been suggested that secretory inflammation of the middle ear deteriorates the basic hearing impairment because of which it should be early diagnosed and surgically treated. Owing to the complex problem of children deafness, the authors recommend that several methods of examination should be applied in the diagnostic procedure in order to determine precisely the auditory threshold and to initiate in time hearing and speech habilitation.

Acoustic Impedance Tests↗

PubMed1989

[Detection of auditory brainstem responses(ABR) threshold with statistical synchrony measure].

Using the method of J. Fridman and his colleagues, a statistical test of auditory brainstem responses (ABR) for detecting auditory threshold has been presented. The synchrony measure (SM) which represents the degree of reproducibility for group averages was used to calculate the selected Fourier components of the group averages from phase variance. The sensitivity of the test was demonstrated on 35 cases with normal ABRs with 60 and 45 dB SL stimulus intensity and in the absence of stimulus from the ipsilateral recordings. The SM of all cases with normal ABR at 60 and 45 dB SL overstopped those in the absence of stimulation. The same procedure was applied to 15 ears with cochlear hearing-loss with (4 ears) and without (9 ears) recruitment and two ears with relatively normal hearing threshold (less than 30 dB BL). Six out of nine ears without recruitment had the SM value at 60 dB SL. stimulus intensity, significantly lower than those with normal ABR.

Adolescent↗

PubMed1986

Age-related changes in human middle latency auditory evoked potentials.

We recorded middle latency auditory evoked potentials (MAEPs) in young (20-40 years) and elderly (60-80 years) subjects with normal hearing. The Pa component was prolonged in latency and markedly enhanced in amplitude in the elderly subjects. No changes were found in Na, or in the binaural interaction of the MAEP. Differences in Pa amplitude and latency were not due exclusively to changes in auditory thresholds, since they were not duplicated by changes in stimulus intensity, and persisted when MAEPs from selected young and old subjects were compared at similar SPL levels. The enhancement of Pa amplitude appears to reflect age-related central modifications in auditory processing.

Adult↗

PubMed2001

[Phasic audiometry in differential diagnosis of sensorineural hearing loss of different etiology].

An original method of differential diagnosis of neurosensory hypoacusis of different etiology is proposed. It is based on registration of the threshold of hearing a short signal moving from 0 degree to 360 degrees against the fluctuation phase of the masking low-frequency tone. In hydrops of the labyrinth phasic audiogram presents as a straight line and demonstrates the lack of auditory thresholds modulation.

Audiometry↗

PubMed2002

Nucleus magnocellularis and nucleus laminaris in Belgian Waterslager and normal strain canaries.

Belgian Waterslager (BWS) canaries are characterized by a mean 30% loss of hair cells in the basilar papilla compared to other canaries, and a corresponding increase in behavioral auditory thresholds. In spite of the large number of missing and damaged sensory cells, there is on average only a 12% reduction in the number of fibers in the VIIIth nerve. In this study, we examined cell number and size, and volume of auditory nuclei, specifically in nucleus magnocellularis and nucleus laminaris in Belgian Waterslager canaries. While the overall anatomical structure and organization of these nuclei and the total number of cells in the non-BWS and BWS canaries were comparable, BWS canaries showed a significant decrease in the volume of the auditory nuclei that was attributed to a reduction in cell size. These results provide further evidence in favor of a role of the sensory epithelium in the maintenance of central auditory structures.

Animals↗

PubMed1999

The underwater audiogram of the West Indian manatee (Trichechus manatus).

The hearing thresholds of two adult manatees were measured using a forced-choice two alternative paradigm and an up/down staircase psychometric method. This is the first behavioral audiogram measured for any Sirenian, as well as the first underwater infrasonic psychometric test with a marine mammal. Auditory thresholds were obtained from 0.4 to 46 kHz, and detection thresholds of possible vibrotactile origin were measured at 0.015-0.2 kHz. The U-shaped audiogram demonstrates an upper limit of functional hearing at 46 kHz with peak frequency sensitivity at 16 and 18 kHz (50 dB re: 1 microPa). The range of best hearing is 6-20 kHz (approximately 9 dB down from maximum sensitivity). Sensitivity falls 20 dB per octave below 0.8 kHz and approximately 40 dB per octave above 26 kHz. The audiogram demonstrates a wider range of hearing and greater sensitivity than was suggested from evoked potential and anatomical studies. High frequency sensitivity may be an adaptation to shallow water, where the propagation of low frequency sound is limited by physical boundary effects. Hearing abilities of manatees and other marine mammals may have also been shaped by ambient and thermal noise curves in the sea. Inadequate hearing sensitivity at low frequencies may be a contributing factor to the manatees' inability to effectively detect boat noise and avoid collisions with boats.

Animals↗

PubMed2005

A novel DFNA9 mutation in the vWFA2 domain of COCH alters a conserved cysteine residue and intrachain disulfide bond formation resulting in progressive hearing loss and site-specific vestibular and central oculomotor dysfunction.

Mutations within the COCH gene (encoding the cochlin protein) lead to auditory and vestibular impairment in the DFNA9 disorder. In this study, we describe the genetic mapping of progressive autosomal dominant sensorineural hearing loss first affecting high-frequency auditory thresholds within a human pedigree to the long arm of chromosome 14 in band q12. A maximal pairwise LOD score of 7.08 was obtained with marker D14S1021. We identified a c.1625G > T mutation in exon 12 of COCH that co-segregates with auditory dysfunction in the pedigree. The mutation results in a predicted p.C542F substitution at an evolutionarily conserved cysteine residue in the C-terminus of cochlin. The c.1625G > T transversion in COCH exon 12 represents the first reported mutation outside of the LCCL domain which is encoded by exons 4 and 5. The 542F mutant cochlin is translated and secreted by transfected mammalian cells. Western blot analysis under non-reducing and reducing conditions suggests that the 542F mutation alters intramolecular cochlin disulfide bond formation. In the vestibular system, a progressive horizontal canal hypofunction and a probable saccular otolith challenge were detected in family members with the c.1625G > T COCH alteration. Abnormal central oculomotor test results in family members with the c.1625G > T COCH alteration imply a possible central nervous system change not previously noted in DFNA9 pedigrees harboring mutations within the LCCL domain.

Amino Acid Sequence↗

PubMed2006

Therapeutic efficacy of intra-cochlear administration of methylprednisolone after acoustic trauma caused by gunshot noise in guinea pigs.

The therapeutic efficacy of cochlear infusion of methylprednisolone (MP) after an impulse noise trauma (170dB SPL peak) was evaluated in guinea pigs. The compound action potential threshold shifts were measured over a 14 days recovery period after the gunshot exposure. For each animal, one of the cochlea was perfused directly into the scala tympani with MP during 7 days via a mini-osmotic pump, whereas the other cochlea was not pump-implanted. The functional study of hearing was supplemented by histological analysis. Forty eight hours after the trauma, significant differences between auditory threshold shifts in the implanted and non-implanted ears were observed for frequencies above 8kHz. At day 7, the difference was significant for only one frequency and no difference was observed after 14 days recovery. Cochleograms showed that the hair cell losses were significantly lower in the MP treated ears. This work indicates that direct infusion of MP into perilymphatic space accelerates hearing recovery, reduces hair cell losses after impulse noise trauma but does not limit permanent threshold shifts.

Action Potentials↗