Pure-tone Detection Thresholds Research Articles

Comprehensive behavioral and physiologic assessment of peripheral and central auditory function in individuals with mild traumatic brain injury

Auditory complaints are frequently reported by individuals with mild traumatic brain injury (mTBI) yet remain difficult to detect in the absence of clinically significant hearing loss. This highlights a growing need to identify sensitive indices of auditory-related mTBI pathophysiology beyond pure-tone thresholds for improved hearing healthcare diagnosis and treatment. Given the heterogeneity of mTBI etiology and the diverse peripheral and central processes required for normal auditory function, the present study sought to determine the audiologic assessments sensitive to mTBI pathophysiology at the group level using a well-rounded test battery of both peripheral and central auditory system function. This test battery included pure-tone detection thresholds, word understanding in quiet, sentence understanding in noise, distortion product otoacoustic emissions (DPOAEs), middle-ear muscle reflexes (MEMRs), and auditory evoked potentials (AEPs), including auditory brainstem responses (ABRs), middle latency responses (MLRs), and late latency responses (LLRs). Each participant also received magnetic resonance imaging (MRI). Compared to the control group, we found that individuals with mTBI had reduced DPOAE amplitudes that revealed a compound effect of age, elevated MEMR thresholds for an ipsilateral broadband noise elicitor, longer ABR Wave I latencies for click and 4 kHz tone burst elicitors, longer ABR Wave III latencies for 4 kHz tone bursts, larger MLR Na and Nb amplitudes, smaller MLR Pb amplitudes, longer MLR Pa latencies, and smaller LLR N1 amplitudes for older individuals with mTBI. Further, mTBI individuals with combined hearing difficulty and noise sensitivity had a greater number of deficits on thalamic and cortical AEP measures compared to those with only one/no self-reported auditory symptoms. This finding was corroborated with MRI, which revealed significant structural differences in the auditory cortical areas of mTBI participants who reported combined hearing difficulty and noise sensitivity, including an enlargement of left transverse temporal gyrus (TTG) and bilateral planum polare (PP). These findings highlight the need for continued investigations toward identifying individualized audiologic assessments and treatments that are sensitive to mTBI pathophysiology.

Temporal integration of tone signals by a killer whale (Orcinus orca).

A psychophysical procedure was used to measure pure-tone detection thresholds for a killer whale (Orcinus orca) as a function of both signal frequency and signal duration. Frequencies ranged between 1 and 100 kHz and signal durations ranged from 50 μs to 2 s, depending on the frequency. Detection thresholds decreased with an increase in signal duration up to a critical duration, which represents the auditory integration time. Integration times ranged from 4 ms at 100 kHz and increased up to 241 ms at 1 kHz. The killer whale data are similar to other odontocete species that have participated in similar experiments. The results have implications for noise impact predictions for signals with durations less than the auditory integration time.

Computer-based musical interval training program for Cochlear implant users and listeners with no known hearing loss.

A musical interval is the difference in pitch between two sounds. The way that musical intervals are used in melodies relative to the tonal center of a key can strongly affect the emotion conveyed by the melody. The present study examines musical interval identification in people with no known hearing loss and in cochlear implant users. Pitch resolution varies widely among cochlear implant users with average resolution an order of magnitude worse than in normal hearing. The present study considers the effect of training on musical interval identification and tests for correlations between low-level psychophysics and higher-level musical abilities. The overarching hypothesis is that cochlear implant users are limited in their ability to identify musical intervals both by low-level access to frequency cues for pitch as well as higher-level mapping of the novel encoding of pitch that implants provide. Participants completed a 2-week, online interval identification training. The benchmark tests considered before and after interval identification training were pure tone detection thresholds, pure tone frequency discrimination, fundamental frequency discrimination, tonal and rhythm comparisons, and interval identification. The results indicate strong correlations between measures of pitch resolution with interval identification; however, only a small effect of training on interval identification was observed for the cochlear implant users. Discussion focuses on improving access to pitch cues for cochlear implant users and on improving auditory training for musical intervals.

Auditory Neuropathy Spectrum Disorders: From Diagnosis to Treatment: Literature Review and Case Reports.

Auditory neuropathy spectrum disorder (ANSD) refers to a range of hearing impairments characterized by deteriorated speech perception, despite relatively preserved pure-tone detection thresholds. Affected individuals usually present with abnormal auditory brainstem responses (ABRs), but normal otoacoustic emissions (OAEs). These electrophysiological characteristics have led to the hypothesis that ANSD may be caused by various dysfunctions at the cochlear inner hair cell (IHC) and spiral ganglion neuron (SGN) levels, while the activity of outer hair cells (OHCs) is preserved, resulting in discrepancies between pure-tone and speech comprehension thresholds. The exact prevalence of ANSD remains unknown; clinical findings show a large variability among subjects with hearing impairment ranging from mild to profound hearing loss. A wide range of prenatal and postnatal etiologies have been proposed. The study of genetics and of the implicated sites of lesion correlated with clinical findings have also led to a better understanding of the molecular mechanisms underlying the various forms of ANSD, and may guide clinicians in better screening, assessment and treatment of ANSD patients. Besides OAEs and ABRs, audiological assessment includes stapedial reflex measurements, supraliminal psychoacoustic tests, electrocochleography (ECochG), auditory steady-state responses (ASSRs) and cortical auditory evoked potentials (CAEPs). Hearing aids are indicated in the treatment of ANSD with mild to moderate hearing loss, whereas cochlear implantation is the first choice of treatment in case of profound hearing loss, especially in case of IHC presynaptic disorders, or in case of poor auditory outcomes with conventional hearing aids.

Anticipatory Baseline Pupil Diameter Is Sensitive to Differences in Hearing Thresholds.

Task-evoked changes in pupil dilation have long been used as a physiological index of cognitive effort. Unlike this response, that is measured during or after an experimental trial, the baseline pupil dilation (BPD) is a measure taken prior to an experimental trial. As such, it is considered to reflect an individual’s arousal level in anticipation of an experimental trial. We report data for 68 participants, ages 18 to 89, whose hearing acuity ranged from normal hearing to a moderate hearing loss, tested over a series 160 trials on an auditory sentence comprehension task. Results showed that BPDs progressively declined over the course of the experimental trials, with participants with poorer pure tone detection thresholds showing a steeper rate of decline than those with better thresholds. Data showed this slope difference to be due to participants with poorer hearing having larger BPDs than those with better hearing at the start of the experiment, but with their BPDs approaching that of the better hearing participants by the end of the 160 trials. A finding of increasing response accuracy over trials was seen as inconsistent with a fatigue or reduced task engagement account of the diminishing BPDs. Rather, the present results imply BPD as reflecting a heightened arousal level in poorer-hearing participants in anticipation of a task that demands accurate speech perception, a concern that dissipates over trials with task success. These data taken with others suggest that the baseline pupillary response may not reflect a single construct.

Suprathreshold auditory processing deficits in noise: Effects of hearing loss and age

People with sensorineural hearing loss generally suffer from a reduced ability to understand speech in complex acoustic listening situations, particularly when background noise is present. In addition to the loss of audibility, a mixture of suprathreshold processing deficits is possibly involved, like altered basilar membrane compression and related changes, as well as a reduced ability of temporal coding. A series of 6 monaural psychoacoustic experiments at 0.5, 2, and 6 kHz was conducted with 18 subjects, divided equally into groups of young normal-hearing, older normal-hearing and older hearing-impaired listeners, aiming at disentangling the effects of age and hearing loss on psychoacoustic performance in noise. Random frequency modulation detection thresholds (RFMDTs) with a low-rate modulator in wide-band noise, and discrimination of a phase-jittered Schroeder-phase from a random-phase harmonic tone complex are suggested to characterize the individual ability of temporal processing. The outcome was compared to thresholds of pure tones and narrow-band noise, loudness growth functions, auditory filter bandwidths, and tone-in-noise detection thresholds. At 500 Hz, results suggest a contribution of temporal fine structure (TFS) to pure-tone detection thresholds. Significant correlation with auditory thresholds and filter bandwidths indicated an impact of frequency selectivity on TFS usability in wide-band noise. When controlling for the effect of threshold sensitivity, the listener's age significantly correlated with tone-in-noise detection and RFMDTs in noise at 500 Hz, showing that older listeners were particularly affected by background noise at low carrier frequencies.

Relation between measures of psychoacoustic abilities and masking release for unprocessed, envelope, and temporal fine-structure speech in listeners with normal and impaired hearing

Léger et al. [J. Acoust. Soc. Am. 135, 2160, 2014] studied masking release in normal-hearing and hearing-impaired listeners using unprocessed speech and speech processed to convey envelope (ENV) or temporal fine-structure (TFS) cues. Consonant identification scores in speech-shaped background noise (continuous and square-wave interrupted at a rate of 10 Hz) indicated a substantial masking release (MR, better performance in the interrupted noise) for all speech types for normal-hearing listeners but only for the TFS speech in most hearing-impaired listeners. The current study was concerned with relating consonant identification scores and masking release to SRTs for sentences in both types of noise as well as to measurements of basic psychoacoustic abilities. These measures included absolute pure-tone detection thresholds, estimates of auditory bandwidth using a notched-noise procedure, and estimates of cochlear compression obtained using a forward-masking paradigm. For both unprocessed and ENV speech, intelligibility scores and MR were correlated with absolute thresholds and auditory bandwidths in the mid-frequency region (but not at a lower frequency). These correlations were less strong for TFS speech intelligibility and did not predict MR. Cochlear compression was not related to speech intelligibility when controlling for the effect of absolute thresholds. [Work supported by NIH R01 DC000117.]

Individual differences reveal correlates of hidden hearing deficits.

Clinical audiometry has long focused on determining the detection thresholds for pure tones, which depend on intact cochlear mechanics and hair cell function. Yet many listeners with normal hearing thresholds complain of communication difficulties, and the causes for such problems are not well understood. Here, we explore whether normal-hearing listeners exhibit such suprathreshold deficits, affecting the fidelity with which subcortical areas encode the temporal structure of clearly audible sound. Using an array of measures, we evaluated a cohort of young adults with thresholds in the normal range to assess both cochlear mechanical function and temporal coding of suprathreshold sounds. Listeners differed widely in both electrophysiological and behavioral measures of temporal coding fidelity. These measures correlated significantly with each other. Conversely, these differences were unrelated to the modest variation in otoacoustic emissions, cochlear tuning, or the residual differences in hearing threshold present in our cohort. Electroencephalography revealed that listeners with poor subcortical encoding had poor cortical sensitivity to changes in interaural time differences, which are critical for localizing sound sources and analyzing complex scenes. These listeners also performed poorly when asked to direct selective attention to one of two competing speech streams, a task that mimics the challenges of many everyday listening environments. Together with previous animal and computational models, our results suggest that hidden hearing deficits, likely originating at the level of the cochlear nerve, are part of "normal hearing."

Binaural masking level difference on hearing impairments compensating by hearing aids

Many researchers reported that the Binaural masking level differences are reduced in pathological conditions, such as sensorineural hearing loss, retro-cochlear hearing loss, central nervous system disease, and so on. In former studies revealed that the amount of BMLDs are about 2–3 dB or in minus. However, for sensorineural hearing loss, the adaptive method may be limited by the hearing thresholds of subjects. Therefore, to eliminate limitation of hearing thresholds, we delivered stimuli by a pair of sound chambers and receiving by hearing aids fitting with NAL-NL1 formula through headphones to subjects. There were eight mild to moderate sensorineural hearing loss subjects (6 females and 2 males, average 62.2 y/o, std. 9.7) participating in this study. With white noise as masker, we conducted pure tone detection thresholds for 125, 250, 500, 1000 and 2000 Hz in S0N0 and STTN0 conditions. The pilot results showed that the threshold differences (S0N0—STTN0) are 4, 6.3, 4.1, 6.9, and 6.3 dB from 125 to 2k Hz. The pilot results revealed that there are BMLDs on SNHLs with compensating by hearing aids. That is to say, this testing method may be used to rule out supra-threshold deficits from sensorineural hearing losses.

Evaluation of Auditory Functions for Royal Canadian Mounted Police Officers

Auditory fitness for duty (AFFD) testing is an important element in an assessment of workers' ability to perform job tasks safely and effectively. Functional hearing is particularly critical to job performance in law enforcement. Most often, assessment is based on pure-tone detection thresholds; however, its validity can be questioned and challenged in court. In an attempt to move beyond the pure-tone audiogram, some organizations like the Royal Canadian Mounted Police (RCMP) are incorporating additional testing to supplement audiometric data in their AFFD protocols, such as measurements of speech recognition in quiet and/or in noise, and sound localization. This article reports on the assessment of RCMP officers wearing hearing aids in speech recognition and sound localization tasks. The purpose was to quantify individual performance in different domains of hearing identified as necessary components of fitness for duty, and to document the type of hearing aids prescribed in the field and their benefit for functional hearing. The data are to help RCMP in making more informed decisions regarding AFFD in officers wearing hearing aids. The proposed new AFFD protocol included unaided and aided measures of speech recognition in quiet and in noise using the Hearing in Noise Test (HINT) and sound localization in the left/right (L/R) and front/back (F/B) horizontal planes. Sixty-four officers were identified and selected by the RCMP to take part in this study on the basis of hearing thresholds exceeding current audiometrically based criteria. This article reports the results of 57 officers wearing hearing aids. Based on individual results, 49% of officers were reclassified from nonoperational status to operational with limitations on fine hearing duties, given their unaided and/or aided performance. Group data revealed that hearing aids (1) improved speech recognition thresholds on the HINT, the effects being most prominent in Quiet and in conditions of spatial separation between target and noise (Noise Right and Noise Left) and least considerable in Noise Front; (2) neither significantly improved nor impeded L/R localization; and (3) substantially increased F/B errors in localization in a number of cases. Additional analyses also pointed to the poor ability of threshold data to predict functional abilities for speech in noise (r² = 0.26 to 0.33) and sound localization (r² = 0.03 to 0.28). Only speech in quiet (r² = 0.68 to 0.85) is predicted adequately from threshold data. Combined with previous findings, results indicate that the use of hearing aids can considerably affect F/B localization abilities in a number of individuals. Moreover, speech understanding in noise and sound localization abilities were poorly predicted from pure-tone thresholds, demonstrating the need to specifically test these abilities, both unaided and aided, when assessing AFFD. Finally, further work is needed to develop empirically based hearing criteria for the RCMP and identify best practices in hearing aid fittings for optimal functional hearing abilities.

C034 The FOX community: A working group for assessing new cochlear implant fitting approaches and practices

People with sensorineural hearing loss generally suffer from a reduced ability to understand speech in complex acoustic listening situations, particularly when background noise is present. In addition to the loss of audibility, a mixture of suprathreshold processing deficits is possibly involved, like altered basilar membrane compression and related changes, as well as a reduced ability of temporal coding. A series of 6 monaural psychoacoustic experiments at 0.5, 2, and 6 kHz was conducted with 18 subjects, divided equally into groups of young normal-hearing, older normal-hearing and older hearing-impaired listeners, aiming at disentangling the effects of age and hearing loss on psychoacoustic performance in noise. Random frequency modulation detection thresholds (RFMDTs) with a low-rate modulator in wide-band noise, and discrimination of a phase-jittered Schroeder-phase from a random-phase harmonic tone complex are suggested to characterize the individual ability of temporal processing. The outcome was compared to thresholds of pure tones and narrow-band noise, loudness growth functions, auditory filter bandwidths, and tone-in-noise detection thresholds. At 500 Hz, results suggest a contribution of temporal fine structure (TFS) to pure-tone detection thresholds. Significant correlation with auditory thresholds and filter bandwidths indicated an impact of frequency selectivity on TFS usability in wide-band noise. When controlling for the effect of threshold sensitivity, the listener's age significantly correlated with tone-in-noise detection and RFMDTs in noise at 500 Hz, showing that older listeners were particularly affected by background noise at low carrier frequencies.

Individual differences in the masking level difference (MLD) with a narrowband masker at 500 or 2000 Hz

The MLD for a narrowband masker is associated with marked individual differences. This study examines factors that might account for these individual differences, including binaural temporal resolution and sensitivity to interaural cues based on time or level. MLD data were collected for 50-Hz wide maskers at 500 and 2000 Hz, gated on for 400-ms. The signal was a pure tone at the center frequency of the masker, of either brief (15-ms) or long (200-ms) duration. Brief signals were coincident with either a local minimum or maximum in the pattern of inherent amplitude modulation. Sensitivity to interaural time and level cues was assessed using similar stimuli, with the exception that the long-duration signal was a 50-Hz band of noise, generated to provide just interaural time cues, just interaural level cues, or both types of cues. Binaural temporal windows were estimated based on pure tone detection thresholds for a brief 500-Hz tone presented at different points in time relative to an abrupt interaural phase transition in a masking noise, bandpass filtered between 100 and 2000 Hz. Relationships between MLD results and those of binaural temporal windows and interaural cues of time and level will be discussed.

Application of the TEN test to hearing-impaired teenagers with severe-to-profound hearing loss: Aplicación de la prueba TEN en adolescentes con hipoacusias severas a profundas

Hearing impairment is often associated with damage to the hair cells of the cochlea. An area of the cochlea with complete loss of function of inner hair cells is known as a ‘dead region’. Dead regions can be identified by measuring detection thresholds for pure tones in quiet and in threshold-equalizing noise (TEN). So far, the TEN test has only been used to identify dead regions in adults with moderate-to-severe hearing impairment. The aim of this study was to assess problems in applying the TEN test to teenagers with longstanding severe-to-profound sensorineural hearing impairment, and to assess the prevalence of dead regions in this population. The subjects had a mean age of 14 years, and there were 13 females and 20 males. The stimuli for the TEN lest were derived from a CD, whose output was routed via a GSI-16 audiometer and an amplifier to Sennheiser HD580 earphones. For each ear of each subject, both absolute thresholds and masked thresholds in the TEN were measured. For the majority of ears, the results were inconclusive at some frequencies, due to the maximum output of the audiometer being reached when measuring the absolute or masked threshold. In almost all cases, the diagnosis was uncertain at some frequencies because the TEN could not be made sufficiently intense to produce significant masking. However, for 23 (70%) subjects, the criteria for a dead region al medium or high frequencies were met in at least one ear. For eight (35%) of these subjects, the criteria were only just met. Sixteen of the 24 subjects with a congenital hearing impairment, and four of the five subjects with an acquired impairment, met the criteria for a dead region. The results suggest that dead regions are relatively common among teenagers with a longstanding hearing impairment.SumarioEl impediments auditive se asocia con frccuencia al daño en las cèlulas ciliadas de la cóclea. Una zona de la cóclea en la quc se pierde completamente la función de las células ciliadas internas se conoce como “region mueria”. Estas regiones pueden identificarse midiendo los umbrales dc detección de tonos puros en ambiente silencioso y con ruido ecualizador de umbrales (TEN). Sin embargo, la prueba TEN solamente se ha usado para identificar regiones muertas en adultos con pérdidas modcradas a severas. Los objetivos de este estudio fueron: la evaluación de problemas aplicando la prueba TEN en adolescentes con pérdidas auditivas sensorineuralcs severas a profundas, y la evaluación de la prevalencia de las regiones muertas en esta poblacion. Los sujetos de estudio, con una cdad promedio de 14 años, fueron 13 mujeres y 20 hombres. Los estimulos para la prueba TEN se enviaron dcsde un CD cuya salida fue eonducida a través de un audiómctro GSI-16 y dc un amplificador, hacia unos auricuiares Sennheisser HD 580. Para cada uno de los sujetos se obtuvieron los umbrales absolulos y enmascarados con la prueba TEN. En la mayoria de los oidos los resultados no fueron concluyentes en algunas frecuencias debido a que la maxima salida del audiómetro sc alcanzó mientras se estaban midiendo esos umbrales absolutos o enmascarados. En la mayoria de los casos el diagnóstico fue incierto en algunas frecueneias porque la prueba TEN no pudo ser lo suticientemente intensa como para producir un enmascaramicnto efectivo. No obslantc en 23 (70%) de los sujetos. el criterio para determinar una region mueria en las freeucncias medias y agudas se alcanzó al mcnos en un oido. En 8 (35%) de estos sujetos, el criterio apenas se alcanzó. Dieeiseis dc los 24 sujetos con un problema auditivo congénito y cuatro de los sujetos con un problema adquirido alcanzaron los criterios para determinar la exislencia dc una region muerta. Los resultados sugieren que esas regiones son relalivamente comunes en los adolescentes con problemas auditivos antiguos.

Dead regions in the cochlea: diagnosis, perceptual consequences, and implications for the fitting of hearing AIDS.

Hearing impairment is often associated with damage to the hair cells in the cochlea. Sometimes there may be complete loss of function of inner hair cells (IHCs) over a certain region of the cochlea; this is called a "dead region". The region can be defined in terms of the range of characteristic frequencies (CFs) of the IHCs and/or neurons immediately adjacent to the dead region. This paper reviews the following topics: the effect of dead regions on the audiogram; methods for the detection and delineation of dead regions based on psychophysical tuning curves (PTCs) and on the measurement of thresholds for pure tones in "threshold equalizing noise" (TEN); effects of dead regions on speech perception; effects of dead regions on the perception of tones; implications of dead regions for fitting hearing aids. The main conclusions are: (1) Dead regions may be relatively common in people with moderate-to-severe sensorineural hearing loss; (2) Dead regions cannot be reliably diagnosed from the audiogram; (3) PTCs provide a useful way of detecting dead regions and defining their boundaries. However, the determination of PTCs is probably too time-consuming to be used for routine diagnosis of dead regions in clinical practice; (4) The measurement of detection thresholds for pure tones in TEN provides a simple method for clinical diagnosis of dead regions; (5) Pure tones with frequencies falling in a dead region do not evoke clear pitch sensations (pitch matching is highly variable) and the perceived pitch is sometimes, but not always, different from "normal". However, ratings of pitch clarity cannot be used as a reliable indicator of a dead region; (6) Amplification of frequencies well inside a high-frequency dead region usually does not improve speech intelligibility, and may sometimes impair it. However, there may be some benefit in amplifying frequencies up to 50 to 100% above the estimated low-frequency edge of a high-frequency dead region; (7) The optimal form of amplification for people with low-frequency dead regions remains somewhat unclear. There may be some benefit from avoiding the amplification of frequencies well inside a dead region; (8) Patients with extensive dead regions are likely to get less benefit from hearing aids than patients without dead regions; (9) For patients with diagnosed dead regions at high frequencies, consideration should be given to use of a hearing aid incorporating frequency transposition and/or compression.

Age-related increase in auditory impairment in monkeys exposed in utero plus postnatally to methylmercury.

Hearing impairment and deafness have been reported as a result of developmental and adult exposure to methylmercury; however, objective assessment of auditory function is generally lacking. This study extends previous research in our laboratory in which monkeys exposed to methylmercury from birth to adulthood exhibited high-frequency hearing impairment. Monkeys (Macaca fascicularis) were exposed throughout gestation and postnatally until 4 years of age to 0, 10, 25, or 50 micrograms/kg/day mercury as methylmercuric chloride. When they were 11 and 19 years of age, pure-tone detection thresholds for six frequencies between 0.125 and 31.5 kHz were determined by means of a psychophysical (behavioral) procedure. At 19 years of age, all five methylmercury-exposed monkeys exhibited elevated pure-tone thresholds compared with controls. Impairment was generally observed across the full range of frequencies. Comparisons of performance at 11 and 19 years revealed relatively greater deterioration in function in treated compared with control monkeys. These results extend previously reported evidence of deficits in auditory function produced by postnatal methylmercury exposure, and describe a pattern of deficit across frequencies different than that observed in the previous study. This study also provides evidence for development or acceleration of impairment of auditory function during aging as a consequence of developmental methylmercury exposure.

Effects of lifetime lead exposure in monkeys on detection of pure tones.

Increased detection thresholds for pure tones were observed in a large cohort of children exposed to lead environmentally while smaller studies in lead-exposed workers have reported conflicting results on assessments of auditory function. Pure tone detection thresholds were determined in a group of monkeys (Macaca fascicularis) dosed with 2 mg/kg/day of lead from birth through testing at 13 years of age. Blood lead concentrations were stable at about 30 micrograms/dl until monkeys were 10-11 years of age at which time they increased to between 50 and 70 micrograms/dl. Five age- and rearing-matched monkeys served as controls. Detection thresholds were determined at six frequencies between 0.125 and 31.5 kHz. Ear phones were fit over both ears, and thresholds were determined for each ear separately. The monkey signaled detection of the tone by breaking contact with a stainless steel bar. Three lead-exposed monkeys exhibited normal pure tone detection functions. Three monkeys had thresholds outside of the control range at some frequencies; there was a tendency for higher frequencies to be differentially more affected. These findings are consistent with reports of elevated pure tone thresholds in humans exposed to lead developmentally, although the effect is smaller than might have been predicted given the concurrent blood lead concentrations of these monkeys.

Low-frequency hearing in California sea lions and harbor seals

Studies on pure-tone detection thresholds were conducted on two female California sea lions and on a harbor seal. The older sea lion and the harbor seal were trained to wear custom-fitted headphones in order to determine minimum audible pressures in a binaural listening task. All three animals were trained to respond to underwater signals at frequencies ranging from 100–1600 Hz at a depth of about 1.5 m. Results were very reliable, owing to a combination of psychophysical threshold determining measures. Sensitivity to low-frequency sounds by both species were 25–30 dB better underwater than in air. The low-frequency hearing of the harbor seal was 2–25 dB better than the older seal lion. At 100 Hz, the sensitivity of the harbor seal was 17 dB superior to that of the younger seal ion, and 23 dB superior to the older seal lion. Results at low frequencies support the notion that the harbor seal (phocid) ear is more water adapted than the sea lion (otariid) ear.

Hair cell regeneration in the European starling ( Sturnus vulgaris): Recovery of pure-tone detection thresholds

Behavioral detection thresholds were obtained from four starlings before, during, and after 11 days of subcutaneous injections of kanamycin. Birds were operantly conditioned to respond to pure-tones ranging in frequency from 0.25 kHz to 7 kHz using the method of constant stimuli and were tested daily for 141 days after the first injection of aminoglycoside. All four birds sustained hearing losses greater than 60 dB at frequencies from 4 kHz to 7 kHz by the end of the 11 day injection schedule. Two birds had a slight shift in threshold at 3 kHz. No change in threshold occurred for any of the birds at lower frequencies. Recovery of detection thresholds began soon after the injections ceased and continued for approximately 50 days. In all four birds there was some degree of permanent hearing loss: 5 dB to 15 dB at frequencies between 4 kHz and 6 kHz, and approximately 25 dB at 7 kHz. Scanning electron microscopy (SEM) was performed at 0 and 5 days post-injection in a separate group of starlings given the same injection schedule. Hair cell loss and damage was observed across the basal 34% to 36% of the basilar papilla. SEM in two behaviorally tested birds sacrificed 142 days after the first injection showed that there was regeneration of hair cells to populate the previously damaged region, but that disorientation of stereocilia bundles in the basal third of the basilar papilla was common. The other two behaviorally tested birds were treated with kanamycin again for 16 days beginning at 142 days after the first injection. Thresholds shifted again, but less than during the first dosing period. SEM of these birds' basilar papillae showed less hair cell loss than observed in the birds given only a single, 11 day dosing of kanamycin. This result suggests that birds may be less susceptible to the ototoxic effects of kanamycin in repeated treatments. In all four birds, the degree and position of damage observed with SEM corresponded with the extent and frequency of hearing loss.

Effects of optic nerve section on susceptibility to retinal light-damage: Williams, T. P. Dodge, J. D., and Bush, R. A. Dept. of Biological Science, Florida State University, Tallahassee, FL 32306

People with sensorineural hearing loss generally suffer from a reduced ability to understand speech in complex acoustic listening situations, particularly when background noise is present. In addition to the loss of audibility, a mixture of suprathreshold processing deficits is possibly involved, like altered basilar membrane compression and related changes, as well as a reduced ability of temporal coding. A series of 6 monaural psychoacoustic experiments at 0.5, 2, and 6 kHz was conducted with 18 subjects, divided equally into groups of young normal-hearing, older normal-hearing and older hearing-impaired listeners, aiming at disentangling the effects of age and hearing loss on psychoacoustic performance in noise. Random frequency modulation detection thresholds (RFMDTs) with a low-rate modulator in wide-band noise, and discrimination of a phase-jittered Schroeder-phase from a random-phase harmonic tone complex are suggested to characterize the individual ability of temporal processing. The outcome was compared to thresholds of pure tones and narrow-band noise, loudness growth functions, auditory filter bandwidths, and tone-in-noise detection thresholds. At 500 Hz, results suggest a contribution of temporal fine structure (TFS) to pure-tone detection thresholds. Significant correlation with auditory thresholds and filter bandwidths indicated an impact of frequency selectivity on TFS usability in wide-band noise. When controlling for the effect of threshold sensitivity, the listener's age significantly correlated with tone-in-noise detection and RFMDTs in noise at 500 Hz, showing that older listeners were particularly affected by background noise at low carrier frequencies.

Pathologic, morphometric and immunocytologic study of white and blue light retinal injuries in monkeys

People with sensorineural hearing loss generally suffer from a reduced ability to understand speech in complex acoustic listening situations, particularly when background noise is present. In addition to the loss of audibility, a mixture of suprathreshold processing deficits is possibly involved, like altered basilar membrane compression and related changes, as well as a reduced ability of temporal coding. A series of 6 monaural psychoacoustic experiments at 0.5, 2, and 6 kHz was conducted with 18 subjects, divided equally into groups of young normal-hearing, older normal-hearing and older hearing-impaired listeners, aiming at disentangling the effects of age and hearing loss on psychoacoustic performance in noise. Random frequency modulation detection thresholds (RFMDTs) with a low-rate modulator in wide-band noise, and discrimination of a phase-jittered Schroeder-phase from a random-phase harmonic tone complex are suggested to characterize the individual ability of temporal processing. The outcome was compared to thresholds of pure tones and narrow-band noise, loudness growth functions, auditory filter bandwidths, and tone-in-noise detection thresholds. At 500 Hz, results suggest a contribution of temporal fine structure (TFS) to pure-tone detection thresholds. Significant correlation with auditory thresholds and filter bandwidths indicated an impact of frequency selectivity on TFS usability in wide-band noise. When controlling for the effect of threshold sensitivity, the listener's age significantly correlated with tone-in-noise detection and RFMDTs in noise at 500 Hz, showing that older listeners were particularly affected by background noise at low carrier frequencies.