Upper Frequency Limit Of Hearing Research Articles

Ultra-high-frequency hearing in seals and sea lions in the context of other secondarily aquatic mammals

The underwater hearing abilities of marine mammals near the upper frequency limit of hearing are poorly understood. While the maximum frequency of hearing is often identified following a sharp roll-off in sensitivity, it is apparent that many marine mammals can perceive high-amplitude tonal sounds above this frequency region. We recently measured underwater detection thresholds in quiet conditions in the 50-180 kHz range for one California sea lion, one spotted seal, and one harbor seal. Absolute sensitivity curves from these subjects exhibited two distinct slope regions at frequencies near the high-frequency hearing limit. The first region is characterized by an initial, rapid decrease in sensitivity with increasing frequency—i.e. a steep slope—while the second shows a much less rapid sensitivity decrease—i.e. a shallower slope. An additional masking study conducted with one of the seals suggested that the initial, rapid decrease in sensitivity is not due to cochlear constraints, as has been proposed, but rather due to constraints on the underlying bone-conduction mechanism. These results can be viewed in the context of the selective pressures influencing ultra-high-frequency hearing in other aquatic mammals, including those capable of specialized echolocation.

Relating Click-Evoked Auditory Brainstem Response Waveforms to Hearing Loss in the Bottlenose Dolphin (Tursiops truncatus)

Hearing sensitivity in captive Atlantic bottlenose dolphins was assessed using a portable electrophysiologic data collection system, a transducer attached to the pan region of the mandible, and non-invasive recording electrodes. The auditory steady-state response (ASSR) was evoked using sinusoidal amplitude-modulated tones at half octave steps from 20–160 kHz and utilized to determine the upper frequency limit of hearing (i.e., the frequency at which threshold was ≤ 120 dB re 1 μPa). An auditory brainstem response (ABR) was then recorded to a moderate-amplitude click (peak-equivalent sound pressure level of 122 dB re 1 μPa) and examined to determine if relationships existed between the upper frequency limit of hearing and the waveform characteristics of the click-evoked ABR. The ASSR and click-evoked ABR were measured in 6 bottlenose dolphins with varying hearing sensitivity and frequency range of hearing. A significant relationship existed between click-evoked ABR wave amplitudes and the upper frequency limit of hearing. Test times for assessment using frequency-specific ASSR and click-evoked ABR were ∼45 minutes and 1 minute, respectively. With further definition of normative data, measurement of click-evoked ABRs could form the basis of an expedited electrophysiologic method for hearing screening in marine mammals.

Relating click-evoked auditory brainstem response waveforms to hearing loss in the bottlenose dolphin (Tursiops truncatus)

Hearing sensitivity in captive Atlantic bottlenose dolphins was assessed using a portable electrophysiologic data collection system, a transducer attached to the pan region of the mandible, and non-invasive recording electrodes. The auditory steady-state response (ASSR) was evoked using sinusoidal amplitude-modulated tones at half octave steps from 20–160 kHz and utilized to determine the upper frequency limit of hearing (i.e., the frequency at which threshold was ≤ 120 dB re 1 μPa). An auditory brainstem response (ABR) was then recorded to a moderate-amplitude click (peak-equivalent sound pressure level of 122 dB re 1 μPa) and examined to determine if relationships existed between the upper frequency limit of hearing and the waveform characteristics of the click-evoked ABR. The ASSR and click-evoked ABR were measured in 6 bottlenose dolphins with varying hearing sensitivity and frequency range of hearing. A significant relationship existed between click-evoked ABR wave amplitudes and the upper frequency limit of hearing. Test times for assessment using frequency-specific ASSR and click-evoked ABR were ∼45 minutes and 1 minute, respectively. With further definition of normative data, measurement of click-evoked ABRs could form the basis of an expedited electrophysiologic method for hearing screening in marine mammals.

Factors Affecting Sensitivity of Distortion-Product Otoacoustic Emissions to Ototoxic Hearing Loss

(1) To determine the ototoxicity detection rate (sensitivity) for distortion-product otoacoustic emissions (DPOAEs) testing in adults who received ototoxic medications and experienced pure-tone threshold changes during the course of treatment; (2) to determine the extent to which DPOAE sensitivity to ototoxicity depends on the type of drug administered (platinum or antibiotic), magnitude of ototoxic threshold shifts, pre-exposure pure-tone threshold, and DPOAE data; and (3) to build a model to predict DPOAE sensitivity. DPOAE and audiometric data were obtained as part of a prospective Veterans Affairs study investigating methods of ototoxicity monitoring. Data were analyzed from 90 ears of 53 subjects receiving ototoxic medications and showing significant hearing changes in at least one ear. Pure-tone threshold data were obtained at frequencies from 0.5 to 20 kHz, using 1/6-octave precision near the upper frequency limit of hearing. DPOAE data are reported for f2's from 0.8 to 8.0 kHz in 1/6-octave increments using primary levels (L1/L2) of 65/59 dB SPL and a primary frequency ratio (f2/f1) of 1.2. Test results were evaluated at various times during drug treatment to determine whether DPOAE level changes were associated with behavioral hearing changes. Univariate and multivariate analysis techniques were used to determine factors that affected DPOAE sensitivity to ototoxic damage. Of the 90 ears examined, 82 (91%) had DPOAEs that could be monitored for changes. Sixty-four of these 82 ears (78%) had DPOAEs that were reduced or absent following drug treatment. DPOAE sensitivity to ototoxicity was unrelated to the type of ototoxic drug administered. Rather, DPOAE sensitivity depended on the magnitude of postexposure hearing changes and on variables related to pre-exposure audiogram and DPOAE measurements. Behavioral hearing changes not detected by DPOAEs were small on average (<7 dB). DPOAE sensitivity was reduced in ears with poorer pre-exposure hearing, and in ears with measurable DPOAE frequencies limited to f2's below 2.5 kHz or more than one octave from the frequency region where hearing change occurred. Results of logistic regression modeling showed that DPOAEs present at f2's greater than 2.5 kHz were associated with the eventual success of ototoxicity monitoring with DPOAEs. However, independent variables examined could not explain differences in the relative timing of behavioral and DPOAE changes. A roughly equivalent proportion of ears experienced DPOAE changes before, during, or after behavioral hearing changes. DPOAEs are a useful screening tool for ototoxicity in adults with pre-exposure hearing loss, but are less sensitive compared with a behavioral test method that targets thresholds near the upper limit of a subject's audible frequency range. Ears successfully monitored for ototoxicity with DPOAEs are those with better pre-exposure hearing, greater postexposure hearing changes, and baseline DPOAEs near the highest behavioral test frequencies and present at high f2's. Results suggest that successful monitoring of ototoxicity with DPOAEs may be predicted clinically by assessing the measurable DPOAE f2 frequency range and its relation to the highest behavioral test frequencies.

Acoustic properties of humpback whale songs

A vertical array of five hydrophones was used to measure the acoustic field in the vertical plane of singing humpback whales. Once a singer was located, two swimmers with snorkel gear were deployed to determine the orientation of the whale and position the boat so that the array could be deployed in front of the whale at a minimum standoff distance of at least 10 m. The spacing of the hydrophones was 7 m with the deepest hydrophone deployed at a depth of 35 m. An eight-channel TASCAM recorder with a bandwidth of 24 kHz was used to record the hydrophone signals. The location (distance and depth) of the singer was determined by computing the time of arrival differences between the hydrophone signals. The maximum source level varied between individual units in a song, with values between 151 and 173 dB re 1 microPa. One of the purposes of this study was to estimate potential sound exposure of nearby conspecifics. The acoustic field determined by considering the relative intensity of higher frequency harmonics in the signals indicated that the sounds are projected in the horizontal direction despite the singer being canted head downward anywhere from about 25 degrees to 90 degrees. High-frequency harmonics extended beyond 24 kHz, suggesting that humpback whales may have an upper frequency limit of hearing as high as 24 kHz.

Auditory response characteristics of the piebald odorous frog and their implications

The piebald odorous frog (Odorrana schmackeri), the large odorous frog (Odorrana livida) and the concave-eared torrent frog (Amolops tormotus) are sympatric species living near the same torrent streams in the vicinity of Mt. Huangshan, China. A recent study demonstrated that A. tormotus can use sound signals involving ultrasonic components for communication in a noisy environment, and another sympatric species, O. livida, can also perceive ultrasonic sound. Here we report data on the hearing range of O. schmackeri by studying auditory evoked potentials and single-unit data from the torus semicircularis. This frog exhibits its two most sensitive peaks at 2 kHz and 3.5-4.0 kHz with thresholds <42 dB SPL, with an upper frequency limit of hearing at 8.5 kHz with threshold of 87 dB SPL. The upper limit is much lower than those of O. livida and A. tormotus, at 22 and 34 kHz, respectively. It suggests that sympatric species may respond differently to similar environmental selection pressures sculpting auditory communication systems.

The acoustic field of singing humpback whales in the vertical plane

A vertical array of five hydrophones was used to measure the acoustic field of singing humpback whales. Once a singer was located, two swimmers with snorkel gear were deployed to determine the orientation of the whale and to position the boat so that the array could be deployed in front of the whale at a minimum standoff distance of 10 m. The spacing of the hydrophones was 7 m with the deepest hydrophone deployed at depth of 35 m. An 8-channel TASCAM recorder having a bandwidth of 24 kHz was used to record the hydrophone signals. The location of the singer was determined by computing the time of arrival differences between the hydrophone signals. The maximum source level varied between individual units in a song, with values between 180 and 190 dB. The acoustic field determined by considering the relative intensity of higher frequency harmonics in the signals indicate that the sounds are projected in the horizontal direction with the singer’s head canted downward 45 to 60°. High-frequency harmonics extended beyond 24 kHz, suggesting that humpback whales may have an upper frequency limit of hearing as high as 24 kHz.

The cochlear outer hair cell motility must be based on a tonic change in the membrane voltage: Implications for the cochlear amplifier

It has been widely assumed that the function of the OHC is to increase the sensitivity and frequency selectivity of the cochlea via a phasic OHC voltage, which controls the soma length. This action is called the cochlear amplifier. According to this view the length of the OHC is assumed to follow the stimulus to the upper frequency limit of hearing, in a phasic manner (cycle by cycle), adding power at the signal frequency. We propose an alternative view that the OHC controls the dynamic range in a parametric, or tonic manner, via the cells axial stiffness. In this case the change in gain seen by the IHC does not require a phasic response at high frequencies. The OHC could mediate a fast acting gain control, via impedance changes, that follows the OHC membrane tonic voltage envelope. Given a level-dependent change in dynamic range (i.e., dynamic range compression), the tuning and sensitivity would necessarily change. Our analysis and conclusions are based upon a re-interpretation of existing mammalian outer hair cell (OHC) studies using a generalized admittance matrix formulation of the OHC, that relates the plasma membrane voltage and current to the soma axial force and velocity.

Evidence for an auditory function of the swimbladder in the cod.

ABSTRACT Saccular microphonic potentials in cod (Gadus morhua) were recorded by means of implanted electrodes during sound stimulation with different swimbladder volumes. To obtain acceptable acoustic conditions, the experiments were conducted at 6 m depth in the sea. Swimbladder volume had no effect on the microphonic potentials at 100 Hz, whereas its effect was marked at higher frequencies. The sound pressure necessary to evoke microphonic potentials just above the electric background noise was about 20 dB higher for the empty bladder, compared to the full bladder at 300 Hz. The microphonic potentials are ultimately linked to excitation of eighth-nerve fibres, and it is concluded that the existence of gas in the cod swimbladder has a positive effect on hearing sensitivity for all frequencies from a lower transient frequency to the upper frequency limit of hearing. Gas in the swimbladder will furthermore extend the audible frequency range. The upper frequency limit for the saccular microphonic potentials is in good agreement with the upper audible frequency limit determined from behavioural audiograms for cod, thus indicating that this frequency cut-off may be due to inadequacy of the peripheral auditory apparatus.