Measuring hearing in the harbor seal (Phoca vitulina): comparison of behavioral and auditory brainstem response techniques

Auditory brainstem response (ABR) and standard behavioral methods were compared by measuring in-air audiograms for an adult female harbor seal (Phoca vitulina). Behavioral audiograms were obtained using two techniques: the method of constant stimuli and the staircase method. Sensitivity was tested from 0.250 to 30 kHz. The seal showed good sensitivity from 6 to 12 kHz [best sensitivity 8.1 dB (re 20 microPa2 x s) RMS at 8 kHz]. The staircase method yielded thresholds that were lower by 10 dB on average than the method of constant stimuli. ABRs were recorded at 2, 4, 8, 16, and 22 kHz and showed a similar best range (8-16 kHz). ABR thresholds averaged 5.7 dB higher than behavioral thresholds at 2, 4, and 8 kHz. ABRs were at least 7 dB lower at 16 kHz, and approximately 3 dB higher at 22 kHz. The better sensitivity of ABRs at higher frequencies could have reflected differences in the seal's behavior during ABR testing and/or bandwidth characteristics of test stimuli. These results agree with comparisons of ABR and behavioral methods performed in other recent studies and indicate that ABR methods represent a good alternative for estimating hearing range and sensitivity in pinnipeds, particularly when time is a critical factor and animals are untrained.     

Simultaneously measured behavioral and electrophysiological hearing thresholds in a bottlenose dolphin (Tursiops truncatus)

Dolphin auditory thresholds obtained via evoked potential audiometry may deviate from behavioral estimates by 20 dB or more. Differences in the sound source, stimulus presentation method, wave form, and duration may partially explain these discrepancies. To determine the agreement between behavioral and auditory evoked potential (AEP) threshold estimates when these parameters are held constant, behavioral and AEP hearing tests were simultaneously conducted in a bottlenose dolphin. Measurements were made in-air, using sinusoidal amplitude-modulated tones continuously projected via a transducer coupled to the pan region of the dolphin's lower jaw. Tone trials were presented using the method of constant stimuli. Behavioral thresholds were estimated using a 50% correct detection. AEP thresholds were based on the envelope following response and 50% correct detection. Differences between AEP and behavioral thresholds were within +/-5 dB, except at 10 kHz (12 dB), 20 kHz (8 dB), 30 kHz (7 dB), and 150 kHz (24 dB). In general, behavioral thresholds were slightly lower, though this trend was not significant. The results demonstrate that when the test environment, sound source, stimulus wave form, duration, presentation method, and analysis are consistent, the magnitude of the differences between AEP and behavioral thresholds is substantially reduced.     

渔业声学回波散射测量系统的宽频带换能器

针对目前渔业声学宽频带回波散射测量系统采用多个不同频带的换能器合成、结构复杂且不方便携带的缺点,本文提出一种使用低机械品质因数、高谐振频率的积层压电致动器作为核心压电元件的"朗之万"型宽带水声换能器。测试结果表明,该换能器适用的频率范围为20 kHz~150 kHz,在三个渔业声学常用频率38 kHz、70 kHz、120 kHz下的-3 dB波束宽度分别为20.0°、11.5°、5.0°,可以满足对常见渔业资源种类的宽带声学回波散射特征的测量要求。     

Speech reception in quiet and in noisy conditions by individuals with noise-induced hearing loss in relation to their tone audiogram.

Tone thresholds and speech-reception thresholds were measured in 200 individuals (400 ears) with noise-induced hearing loss. The speech-reception thresholds were measured in a quiet condition and in noise with a speech spectrum at levels of 35, 50, 65, and 80 dBA. The tone audiograms could be described by three principal components: hearing loss in the regions above 3 kHz, from 1 to 3 kHz and below 1 kHz; the speech thresholds could be described by two components: speech reception in quiet and speech reception in noise at 50-80 dBA. Hearing loss above 1 kHz was related to speech reception in noise; hearing loss at and below 1 kHz to speech reception in quiet. The correlation between the speech thresholds in quiet and in noise was only R = 0.45. An adequate predictor of the speech threshold in noise, the primary factor in the hearing handicap, was the pure-tone average at 2 and 4 kHz (PTA2,4, R = 0.72). The minimum value of the prediction error for any tone-audiometric predictor of this speech threshold was 1.2 dB (standard deviation). The prediction could not be improved by taking into account the critical ratio for low-frequency noise nor by its upward spread of masking. The prediction error is due to measurement error and to a factor common to both ears. The latter factor is ascribed to cognitive skill in speech reception. Hearing loss above 10 to 15 dB HL (hearing level) already shows an effect on the speech threshold in noise, a noticeable handicap is found at PTA2,4 = 30 dB HL.     

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.     

Detecting high-frequency hearing loss with click-evoked otoacoustic emissions

In contrast to clinical click-evoked otoacoustic emission (CEOAE) tests that are inaccurate above 4-5 kHz, a research procedure measured CEOAEs up to 16 kHz in 446 ears and predicted the presence/absence of a sensorineural hearing loss. The behavioral threshold test that served as a reference to evaluate CEOAE test accuracy used a yes-no task in a maximum-likelihood adaptive procedure. This test was highly efficient between 0.5 and 12.7 kHz: Thresholds measured in 2 min per frequency had a median standard deviation (SD) of 1.2-1.5 dB across subjects. CEOAE test performance was assessed by the area under the receiver operating characteristic curve (AUC). The mean AUC from 1 to 10 kHz was 0.90 (SD=0.016). AUC decreased to 0.86 at 12.7 kHz and to 0.7 at 0.5 and 16 kHz, possibly due in part to insufficient stimulus levels. Between 1 and 12.7 kHz, the medians of the magnitude difference in CEOAEs and in behavioral thresholds were <4 dB. The improved CEOAE test performance above 4-5 kHz was due to retaining the portion of the CEOAE response with latencies as short as 0.3 ms. Results have potential clinical significance in predicting hearing status from at least 1 to 10 kHz using a single CEOAE response.     

Auditory evoked potentials in two short-finned pilot whales (Globicephala macrorhynchus)

The hearing sensitivities of two short-finned pilot whales (Globicephala macrorhynchus) were investigated by measuring auditory evoked potentials generated in response to clicks and sinusoidal amplitude modulated (SAM) tones. The first whale tested, an adult female, was a long-time resident at SeaWorld San Diego with a known health history. Click-evoked responses in this animal were similar to those measured in other echolocating odontocetes. Auditory thresholds were comparable to dolphins of similar age determined with similar evoked potential methods. The region of best sensitivity was near 40 kHz and the upper limit of functional hearing was between 80 and 100 kHz. The second whale tested, a juvenile male, was recently stranded and deemed non-releasable. Click-evoked potentials were not detected in this animal and testing with SAM tones suggested severe hearing loss above 10 kHz.     

Auditory and behavioral responses of California sea lions (Zalophus californianus) to single underwater impulses from an arc-gap transducer

A behavioral response paradigm was used to measure underwater hearing thresholds in two California sea lions (Zalophus californianus) before and after exposure to underwater impulses from an arc-gap transducer. Preexposure and postexposure hearing thresholds were compared to determine if the subjects experienced temporary shifts in their masked hearing thresholds (MTTS). Hearing thresholds were measured at 1 and 10 kHz. Exposures consisted of single underwater impulses produced by an arc-gap transducer referred to as a "pulsed power device" (PPD). The electrical charge of the PPD was varied from 1.32 to 2.77 kJ; the distance between the subject and the PPD was varied over the range 3.4 to 25 m. No MTTS was observed in either subject at the highest received levels: peak pressures of approximately 6.8 and 14 kPa, rms pressures of approximately 178 and 183 dB re: 1 microPa, and total energy fluxes of 161 and 163 dB re: 1 microPa2s for the two subjects. Behavioral reactions to the tests were observed in both subjects. These reactions primarily consisted of temporary avoidance of the site where exposure to the PPD impulse had previously occurred.     

Frequency discrimination learning in children

Psychoacoustic thresholds of pure tone frequency discrimination (FD) in children are elevated relative to those of adults. It has been shown that it is possible to improve FD thresholds in adults, following a single (subhour) training session. To determine whether FD thresholds in children may be improved by training and, consequently, reduced to adult levels, 100 normally hearing 6- to 11-year-old children and adults received approximately 1 h of training on a FD task at 1 kHz. At the start of training, a quarter of all child participants had FD thresholds that resembled those of naive adults (adult-like subgroup). Another quarter achieved thresholds that were adult-like at some point during training (trainable subgroup). For the remainder (nonadult-like subgroup), thresholds did not reach those of naive adult listeners at any point in the training session. Subgroup membership was linked to the influence of three factors-age, nonverbal IQ, and attention. However, across subgroups, learning was found not to generalize to either a different standard frequency (4 kHz) or a variable (roving) presentation paradigm. The results indicate that it is possible for some children to achieve FD thresholds comparable to those of naive adults, either natively or after limited training.     

The effect of basilar-membrane nonlinearity on the shapes of masking period patterns in normal and impaired hearing

Masking period patterns (MPPs) were measured in listeners with normal and impaired hearing using amplitude-modulated tonal maskers and short tonal probes. The frequency of the masker was either the same as the frequency of the probe (on-frequency masking) or was one octave below the frequency of the probe (off-frequency masking). In experiment 1, MPPs were measured for listeners with normal hearing using different masker levels. Carrier frequencies of 3 and 6 kHz were used for the masker. The probe had a frequency of 6 kHz. For all masker levels, the off-frequency MPPs exhibited deeper and longer valleys compared with the on-frequency MPPs. Hearing-impaired listeners were tested in experiment 2. For some hearing-impaired subjects, masker frequencies of 1.5 kHz and 3 kHz were paired with a probe frequency of 3 kHz. MPPs measured for listeners with hearing loss had similar shapes for on- and off-frequency maskers. It was hypothesized that the shapes of MPPs reflect nonlinear processing at the level of the basilar membrane in normal hearing and more linear processing in impaired hearing. A model assuming different cochlear gains for normal versus impaired hearing and similar parameters of the temporal integrator for both groups of listeners successfully predicted the MPPs.     

The effect of signal duration on the underwater detection thresholds of a harbor porpoise (Phocoena phocoena) for single frequency-modulated tonal signals between 0.25 and 160 kHz

The underwater hearing sensitivity of a young male harbor porpoise for tonal signals of various signal durations was quantified by using a behavioral psychophysical technique. The animal was trained to respond only when it detected an acoustic signal. Fifty percent detection thresholds were obtained for tonal signals (15 frequencies between 0.25-160 kHz, durations 0.5-5000 ms depending on the frequency; 134 frequency-duration combinations in total). Detection thresholds were quantified by varying signal amplitude by the 1-up 1-down staircase method. The hearing thresholds increased when the signal duration fell below the time constant of integration. The time constants, derived from an exponential model of integration [Plomp and Bouman, J. Acoust. Soc. Am. 31, 749-758 (1959)], varied from 629 ms at 2 kHz to 39 ms at 64 kHz. The integration times of the porpoises were similar to those of other mammals including humans, even though the porpoise is a marine mammal and a hearing specialist. The results enable more accurate estimations of the distances at which porpoises can detect short-duration environmental tonal signals. The audiogram thresholds presented by Kastelein et al. [J. Acoust. Soc. Am. 112, 334-344 (2002)], after correction for the frequency bandwidth of the FM signals, are similar to the results of the present study for signals of 1500 ms duration. Harbor porpoise hearing is more sensitive between 2 and 10 kHz, and less sensitive above 10 kHz, than formerly believed.     

Age changes in pure-tone hearing thresholds in a longitudinal study of normal human aging

Hearing thresholds were obtained on 813 adult males (20-95 years) measured at 11 frequencies ranging from 0.125-8 kHz from pure-tone audiograms collected over a 20-year period from 1968 to 1987. Audiograms taken at two to six different ages spanning a maximum observation period of 15 years were obtained for each male belonging to one of seven different age groups (20,30,...,80 years) based on the age of initial observation. The males were participants in the Baltimore Longitudinal study of Aging (BLSA), a multidisciplinary community-based study of normal human aging. Changes in hearing thresholds occurred in all age groups during the 15-year follow-up period. For example, at 0.5 and 8 kHz for combined left and right ears there was an average longitudinal loss of 5.7-7.6 and 5.1-21.1 dB, respectively, for 20-year-olds, 10.0-12.7 and 35.2-53.0 dB for 50-year-olds, and 22.9-48.5 and 69.0-84.5 dB for 80-year-olds. As in results from previous cross-sectional studies, hearing loss in the males 70 years and older is greatest at the highest frequencies. The rate of change for these older males is faster in the speech-range frequencies 0.5-2 kHz than in the higher frequencies, since their hearing has already diminished at the high frequencies.     

Amplitude modulation thresholds in chinchillas with high-frequency hearing loss

Estimates of auditory temporal resolution were obtained from normal chinchillas using sinusoidally amplitude modulated noise. Afterwards, the animals were exposed to noise whose bandwidth was progressively increased toward the low frequencies in octave steps. The first exposure was to an octave band of noise centered at 8 kHz. Three additional octave bands of noise were subsequently added to the original exposure in order to progressively increase the extent of the high-frequency hearing loss. The first exposure produced a temporary hearing loss of 50 to 60 dB near 8 kHz and elevated the amplitude modulation thresholds primarily at intermediate (128 Hz) modulation frequencies. Successive noise exposures extended the temporary hearing loss toward lower frequencies, but there was little further deterioration in the amplitude modulation function until the last exposure when the hearing loss spread to 1 kHz. The degradation in the amplitude modulation function observed after the last exposure, however, was due to a reduction in the sensation level of the test signal rather than to a decrease in the hearing bandwidth. The results of this study suggest that the high-frequency regions of the cochlea may be important for temporal resolution.     

Temporary shift in masked hearing thresholds in odontocetes after exposure to single underwater impulses from a seismic watergun

A behavioral response paradigm was used to measure masked underwater hearing thresholds in a bottlenose dolphin (Tursiops truncatus) and a white whale (Delphinapterus leucas) before and after exposure to single underwater impulsive sounds produced from a seismic watergun. Pre- and postexposure thresholds were compared to determine if a temporary shift in masked hearing thresholds (MTTS), defined as a 6-dB or larger increase in postexposure thresholds, occurred. Hearing thresholds were measured at 0.4, 4, and 30 kHz. MTTSs of 7 and 6 dB were observed in the white whale at 0.4 and 30 kHz, respectively, approximately 2 min following exposure to single impulses with peak pressures of 160 kPa, peak-to-peak pressures of 226 dB re 1 microPa, and total energy fluxes of 186 dB re 1 microPa2 x s. Thresholds returned to within 2 dB of the preexposure value approximately 4 min after exposure. No MTTS was observed in the dolphin at the highest exposure conditions: 207 kPa peak pressure, 228 dB re 1 microPa peak-to-peak pressure, and 188 dB re 1 microPa2 x s total energy flux.     

Audiometric thresholds among a Canadian sample of 10 to 17 year old students

A total of 237 students, 10 to 17 years of age, from 14 schools underwent hearing evaluations. Otoscopic examination, tympanometry and air-conduction pure tone audiometry was conducted at low (0.5, 1, 2 kHz) and high (4 and 8 kHz) frequencies. In all schools, hearing thresholds were measured with headphones in a portable audiometric booth. Socio-demographic information from students and their parents were collected using questionnaires. Overall, the prevalence of any hearing loss greater than 15 dB was 22.3% for low or high frequency pure tone averages. Self-reported symptoms of hearing loss, such as tinnitus, difficulty following a conversation with background noise, and having to turn up the TV/radio more than in the past, were associated with audiometric thresholds, most notably at 4 kHz. These study findings are among the first to provide a detailed characterization of hearing status in a sample of youth in a Canadian demographic.     

Behavioral and auditory evoked potential audiograms of a false killer whale (Pseudorca crassidens)

Behavioral and auditory evoked potential (AEP) audiograms of a false killer whale were measured using the same subject and experimental conditions. The objective was to compare and assess the correspondence of auditory thresholds collected by behavioral and electrophysiological techniques. Behavioral audiograms used 3-s pure-tone stimuli from 4 to 45 kHz, and were conducted with a go/no-go modified staircase procedure. AEP audiograms used 20-ms sinusoidally amplitude-modulated tone bursts from 4 to 45 kHz, and the electrophysiological responses were received through gold disc electrodes in rubber suction cups. The behavioral data were reliable and repeatable, with the region of best sensitivity between 16 and 24 kHz and peak sensitivity at 20 kHz. The AEP audiograms produced thresholds that were also consistent over time, with range of best sensitivity from 16 to 22.5 kHz and peak sensitivity at 22.5 kHz. Behavioral thresholds were always lower than AEP thresholds. However, AEP audiograms were completed in a shorter amount of time with minimum participation from the animal. These data indicated that behavioral and AEP techniques can be used successfully and interchangeably to measure cetacean hearing sensitivity.     

Ultrasound sensitivity in the cricket, Eunemobius carolinus (Gryllidae, Nemobiinae)

Extracellular recordings from the cervical connectives in both long- and short-winged E. carolinus reveal auditory units that are sensitive to frequencies > 15 kHz with best sensitivity at 35 kHz (79 dB SPL threshold). Stimuli in this frequency range also elicit a startle response in long-winged individuals flying on a tether. For single-pulse stimuli, startle and neck connective thresholds decrease with increasing ultrasound duration, consistent with the operation of an exponential integrator with a approximately 32.5-ms time constant. There is evidence for adaptation to long duration pulses (> 20 ms) in the neck connectives, however, as it is more difficult to elicit responses to the later stimuli of a series. For paired-pulse stimuli consisting of 1-ms pulses of 40 kHz, temporal integration was demonstrated for pulse separations < 5 ms. For longer pulse separations, startle thresholds were elevated by 3 dB and appear to be optimally combined. Startle thresholds to 5 ms frequency modulated (FM) sweeps (60-30 kHz) and pure tone pulses (40 kHz) did not differ. The characteristics and sensitivity of this ultrasound-induced startle response did not differ between males and females. As in some other tympanate insects, ultrasound sensitivity in E. carolinus presumably functions in the context of predation from echolocating bats.     

Forward- and simultaneous-masked thresholds in bandlimited maskers in subjects with normal hearing and cochlear hearing loss

Forward- and simultaneous-masked thresholds were measured at 0.5 and 2.0 kHz in bandpass maskers as a function of masker bandwidth and in a broadband masker with the goal of estimating psychophysical suppression. Suppression was operationally defined in two ways: (1) as a change in forward-masked threshold as a function of masker bandwidth, and (2) as a change in effective masker level with increased masker bandwidth, taking into account the nonlinear growth of forward masking. Subjects were younger adults with normal hearing and older adults with cochlear hearing loss. Thresholds decreased as a function of masker bandwidth in forward masking, which was attributed to effects of suppression; thresholds remained constant or increased slightly with increasing masker bandwidth in simultaneous masking. For subjects with normal hearing, slightly larger estimates of suppression were obtained at 2.0 kHz rather than at 0.5 kHz. For hearing-impaired subjects, suppression was reduced in regions of hearing loss. The magnitude of suppression was strongly correlated with the absolute threshold at the signal frequency, but did not vary with thresholds at frequencies remote from the signal. The results suggest that measuring forward-masked thresholds in bandlimited and broadband maskers may be an efficient psychophysical method for estimating suppression.     

High-frequency audiometric assessment of a young adult population

The hearing thresholds of 37 young adults (18-26 years) were measured at 13 frequencies (8, 9,10,...,20 kHz) using a newly developed high-frequency audiometer. All subjects were screened at 15 dB HL at the low audiometric frequencies, had tympanometry within normal limits, and had no history of significant hearing problems. The audiometer delivers sound from a driver unit to the ear canal through a lossy tube and earpiece providing a source impedance essentially equal to the characteristic impedance of the tube. A small microphone located within the earpiece is used to measure the response of the ear canal when an impulse is applied at the driver unit. From this response, a gain function is calculated relating the equivalent sound-pressure level of the source to the SPL at the medial end of the ear canal. For the subjects tested, this gain function showed a gradual increase from 2 to 12 dB over the frequency range. The standard deviation of the gain function was about 2.5 dB across subjects in the lower frequency region (8-14 kHz) and about 4 dB at the higher frequencies. Cross modes and poor fit of the earpiece to the ear canal prevented accurate calibration for some subjects at the highest frequencies. The average SPL at threshold was 23 dB at 8 kHz, 30 dB at 12 kHz, and 87 dB at 18 kHz. Despite the homogeneous nature of the sample, the younger subjects in the sample had reliably better thresholds than the older subjects. Repeated measurements of threshold over an interval as long as 1 month showed a standard deviation of 2.5 dB at the lower frequencies (8-14 kHz) and 4.5 dB at the higher frequencies.     

Development of auditory sensitivity in budgerigars (Melopsittacus undulatus)

Auditory feedback influences the development of vocalizations in songbirds and parrots; however, little is known about the development of hearing in these birds. The auditory brainstem response was used to track the development of auditory sensitivity in budgerigars from hatch to 6 weeks of age. Responses were first obtained from 1-week-old at high stimulation levels at frequencies at or below 2 kHz, showing that budgerigars do not hear well at hatch. Over the next week, thresholds improved markedly, and responses were obtained for almost all test frequencies throughout the range of hearing by 14 days. By 3 weeks posthatch, birds' best sensitivity shifted from 2 to 2.86 kHz, and the shape of the auditory brainstem response (ABR) audiogram became similar to that of adult budgerigars. About a week before leaving the nest, ABR audiograms of young budgerigars are very similar to those of adult birds. These data complement what is known about vocal development in budgerigars and show that hearing is fully developed by the time that vocal learning begins.