Vertical auditory acuity of the bottlenose dolphin

The accuracy in locating underwater sounds in the vertical median plane was determined for the Black Sea bottlenose dolphin Tursiops truncatus trained by operant conditioning with food reinforcement. The minimal perceived angles for 1-s tone signals were 2.5° at 5 or 20 kHz and 2.0° at 120 kHz; for 1-s trains of clicks centered at 120 kHz the acuity was still better, ～1.5°. Dolphins may locate different sounds using different yet equally efficient mechanisms, and they are the best in analyzing the acoustic space among marine mammals studied.     

The ontogenetic development of auditory sensitivity, vocalization and acoustic communication in the labyrinth fish Trichopsis vittata

The anabantoid fish Trichopsis vittata starts vocalizing as 8-week-old juveniles. In order to determine whether juveniles are able to detect conspecific sounds, hearing sensitivities were measured in six size groups utilizing the auditory brainstem response-recording technique. Results were compared to sound pressure levels and spectra of sounds recorded during fighting. Auditory evoked potentials were present in all size groups and complete audiograms were obtained starting with 0.18 to 0.30 g juveniles. Auditory sensitivity during development primarily increased between 0.8 kHz and 3.0 kHz. The most sensitive frequency within this range shifted from 2.5 kHz to 1.5 kHz, whereas thresholds decreased by 14 dB. Sound production, on the other hand, started at 0.1 g and sound power spectra at dominant frequencies increased by 43 dB, while dominant frequencies shifted from 3 kHz to 1.5 kHz. Comparisons between audiograms and sound power spectra in similar-sized juveniles revealed no clear match between most sensitive frequencies and dominant frequencies of sounds. This also revealed that juveniles cannot detect conspecific sounds below the 0.31 to 0.65 g size class. These results indicate that auditory sensitivity develops prior to the ability to vocalize and that vocalization occurs prior to the ability to communicate acoustically.     

Correlation between auditory sensitivity and vocalization in anabantoid fishes

Several anabantoid species produce broad-band sounds with high-pitched dominant frequencies (0.8–2.5 kHz), which contrast with generally low-frequency hearing abilities in (perciform) fishes. Utilizing a recently developed auditory brainstem response recording-technique, auditory sensitivities of the gouramis Trichopsis vittata, T. pumila, Colisa lalia, Macropodus opercularis and Trichogaster trichopterus were investigated and compared with the sound characteristics of the respective species. All five species exhibited enhanced sound-detecting abilities and perceived tone bursts up to 5 kHz, which qualifies this group as hearing specialists. All fishes possessed a high-frequency sensitivity maximum between 800 Hz and 1500 Hz. Lowest hearing thresholds were found in T. trichopterus (76 dB re 1 μPa at 800 Hz). Dominant frequencies of sounds correspond with the best hearing bandwidth in T. vittata (1–2 kHz) and C. lalia (0.8–1 kHz). In the smallest species, T. pumila, dominant frequencies of acoustic signals (1.5–2.5 kHz) do not match lowest thresholds, which were below 1.5 kHz. However, of all species studied, T. pumila had best hearing sensitivity at frequencies above 2 kHz. The association between high-pitched sounds and hearing may be caused by the suprabranchial air-breathing chamber, which, lying close to the hearing and sonic organs, enhances both sound perception and emission at its resonant frequency. Accepted: 26 November 1997     

Multiple specializations in the peripheral auditory system of the CF-FM bat,Pteronotus parnellii

Summary Cochlear microphonic (CM) and evoked neural potentials (N₁) were recorded from the cochlear aqueduct of awakePteronotus parnellii. The CM audiograms obtained with continuous sounds had more or less uniform thresholds except for a sharp threshold notch at about 60 kHz (Fig. 1). When brief tone bursts were presented, the envelopes of the CM responses were always similar to the envelopes of the applied signals except when tone bursts having frequencies at or close to the frequency of the tuned sensitivity notch were presented (i.e., 59–63 kHz). The CM rise-decay times for frequencies around 60kHz were much longer than those of the presented signals (Fig. 2). The prolonged decay times are thought to be due to the ringing of the basilar membrane resulting from a mechanical resonance in the cochlea.The evoked neural potential audiograms (N₁-on and N₁-off responses) differed considerably from the CM audiogram. Of particular importance is the N₁-off audiogram which exhibited very sharp tuning in four frequency regions: 31–33 kHz, 60–63 kHz, 71–73 kHz, and 91–92 kHz (Fig. 5). The frequencies evoking the lowest thresholds of the CM and N₁-off (in the 60 kHz region) were either identical or differed by only 100–400 Hz.The sharp tuning in the 60 kHz region of both the CM and N₁ audiograms could be eliminated by presenting 90–100 dB continuous sounds for one min but only if the signal frequency was equal to the tuned frequency of the CM audiogram (Figs. 8–13). Presenting intense sounds having frequencies above or below the tuned 60kHz region had no effect on the audiogram. The overstimulation procedure had remarkably specific effects on the CM and N₁-off audiograms causing the greatest threshold increases at the 60 kHz tuned frequency and progressively smaller threshold changes on the slopes of the tuned notch.Assuming that the sharp changes of the N₁-off thresholds reflect some important underlying mechanism, the N₁-off audiograms demonstrate multiple specializations in the peripheral auditory system ofPteronotus with the bat possessing at least three and possibly four sharply tuned regions. With regard to mechanism, the tuned notch in the CM audiogram, the curious CM rise-decay times evoked by tone bursts, and the ease with which the 60 kHz sensitivity notch can be eliminated all argue strongly in favor of a mechanical resonance in the cochlea which is responsible for the sharp tuning around 60 kHz. On the other hand, the absence of tuned notches in the 30 kHz and 90 kHz regions of the CM audiogram together with the absence of any discernable ringing of the CM potentials evoked by 30 kHz and 90 kHz tone bursts both argue against a resonance mechanism for the tuning at these harmonically related frequency regions. Finally, the fact that overstimulating the 60 kHz region had no discernable effect on the N₁-off tuning at 30 kHz and 90 kHz demonstrates that the mechanism responsible for the tuned regions at 30 kHz and 90 kHz are independent of the resonance feature of the cochlea at 60 kHz.Abbreviations BF best frequency - CF constant frequency - CM cochlear microphonics - CM-aft after-response of the CM - FM frequency modulated - N ₁ evoked neural potentials We thank Professor Alvin Novick for the generous support provided during the conduct of these experiments. We also thank Professor Gerhard Neuweiler and Dr. Gerd Schuller for their helpful comments and suggestions. Supported by PHS Grant NB7616 11.     

Echo thresholds of the precedence effect in the vertical plane

Echo thresholds were measured for two configurations of loudspeakers in the vertical plane. The first configuration was characterized by the lead sound presentation from a loudspeaker placed in front of a subject, whereas the lag sound was presented from the loudspeaker above the subject's head. In the second configuration, the lead and lag sounds were presented from the same loudspeakers but in reverse order. All the stimuli were broadband noise bursts in the frequency range of 5-20 kHz. Burst durations were 5, 10, 20, and 100 ms. Average echo thresholds differences were significant only for the signals of 100 ms in duration (F (1, 16) = 6.28; p < 0.05). For the other signals (5, 10, 20 ms), there was no significant effect of location of lead and lag signals (p > 0.05).     

Acoustic communication and the evolution of hearing in fishes

Fishes have evolved a diversity of sound-generating organs and acoustic signals of various temporal and spectral content. Additionally, representatives of many teleost families such as otophysines, anabantoids, mormyrids and holocentrids possess accessory structures that enhance hearing abilities by acoustically coupling air-filled cavities to the inner ear. Contrary to the accessory hearing structures such as Weberian ossicles in otophysines and suprabranchial chambers in anabantoids, sonic organs do not occur in all members of these taxa. Comparison of audiograms among nine representatives of seven otophysan families from four orders revealed major differences in auditory sensitivity, especially at higher frequencies (> 1 kHz) where thresholds differed by up to 50 dB. These differences showed no apparent correspondence to the ability to produce sounds (vocal versus non-vocal species) or to the spectral content of species-specific sounds. In anabantoids, the lowest auditory thresholds were found in the blue gourami Trichogaster trichopterus, a species not thought to be vocal. Dominant frequencies of sounds corresponded with optimal hearing bandwidth in two out of three vocalizing species. Based on these results, it is concluded that the selective pressures involved in the evolution of accessory hearing structures and in the design of vocal signals were other than those serving to optimize acoustic communication.     

Frequency discrimination by the bottle-nosed dolphin and the Northern fur seal depending on sound parameters and sound conduction pathways

Underwater differential frequency hearing thresholds in the Black Sea bottle-nosed dolphin (Tursiops truncatus p.) and the northern fur seal (Callorhinus ursinus) were measured depending on signal frequency and sound conduction pathways. The measurements were performed by the method of instrumental conditioned reflexes with food reinforcement under conditions of full and partial (with heads out of water at sound conduction through body tissues) submergence of animals into water. It was shown that in a frequency range of 5-100 kHz, underwater differential frequency hearing thresholds of the bottle-nosed dolphin changed from 0.46-0.60% to 0.21-0.34% and depended little on sound conduction pathways. The minimum underwater differential frequency hearing thresholds of the northern fur seal corresponded to the frequencies of maximum hearing sensitivity, changed from 1.7% to 1-2.3% in a frequency range of 1-20 kHz, sharply increased at the edges of the frequency hearing perception range, and depended little (in a range of 5-40 kHz) on sound conduction pathways. Thus, underwater sounds propagating through the body tissues of dolphin and fur seal reach the inner ear.     

Hearing in the sea otter (Enhydra lutris): auditory profiles for an amphibious marine carnivore

In this study we examine the auditory capabilities of the sea otter (Enhydra lutris), an amphibious marine mammal that remains virtually unstudied with respect to its sensory biology. We trained an adult male sea otter to perform a psychophysical task in an acoustic chamber and at an underwater apparatus. Aerial and underwater audiograms were constructed from detection thresholds for narrowband signals measured in quiet conditions at frequencies from 0.125–40 kHz. Aerial hearing thresholds were also measured in the presence of octave-band masking noise centered at eight signal frequencies (0.25–22.6 kHz) so that critical ratios could be determined. The aerial audiogram of the sea otter resembled that of sea lions and showed a reduction in low-frequency sensitivity relative to terrestrial mustelids. Best sensitivity was ?1 dB re 20 µPa at 8 kHz. Under water, hearing sensitivity was significantly reduced when compared to sea lions and other pinniped species, demonstrating that sea otter hearing is primarily adapted to receive airborne sounds. Critical ratios were more than 10 dB higher than those measured for pinnipeds, suggesting that sea otters are less efficient than other marine carnivores at extracting acoustic signals from background noise, especially at frequencies below 2 kHz.     

Sex-Specific Differences in Agonistic Behaviour,Sound Production and Auditory Sensitivity in the Callichthyid Armoured Catfish Megalechis thoracata

Background

Data on sex-specific differences in sound production, acoustic behaviour and hearing abilities in fishes are rare. Representatives of numerous catfish families are known to produce sounds in agonistic contexts (intraspecific aggression and interspecific disturbance situations) using their pectoral fins. The present study investigates differences in agonistic behaviour, sound production and hearing abilities in males and females of a callichthyid catfish.

Methodology/Principal Findings

Eight males and nine females of the armoured catfish Megalechis thoracata were investigated. Agonistic behaviour displayed during male-male and female-female dyadic contests and sounds emitted were recorded, sound characteristics analysed and hearing thresholds measured using the auditory evoked potential (AEP) recording technique. Male pectoral spines were on average 1.7-fold longer than those of same-sized females. Visual and acoustic threat displays differed between sexes. Males produced low-frequency harmonic barks at longer distances and thumps at close distances, whereas females emitted broad-band pulsed crackles when close to each other. Female aggressive sounds were significantly shorter than those of males (167 ms versus 219 to 240 ms) and of higher dominant frequency (562 Hz versus 132 to 403 Hz). Sound duration and sound level were positively correlated with body and pectoral spine length, but dominant frequency was inversely correlated only to spine length. Both sexes showed a similar U-shaped hearing curve with lowest thresholds between 0.2 and 1 kHz and a drop in sensitivity above 1 kHz. The main energies of sounds were located at the most sensitive frequencies.

Conclusions/Significance

Current data demonstrate that both male and female M. thoracata produce aggressive sounds, but the behavioural contexts and sound characteristics differ between sexes. Sexes do not differ in hearing, but it remains to be clarified if this is a general pattern among fish. This is the first study to describe sex-specific differences in agonistic behaviour in fishes.     

Auditory brainstem responses to airborne sounds in the aquatic frog Xenopus laevis: correlation with middle ear characteristics

In this study we recorded auditory brainstem responses to airborne sounds to determine the hearing sensitivity of Xenopus laevis frogs and correlated their hearing profiles with middle ear characteristics. In newly metamorphosed frogs (body mass 0.5–0.76 gm, snout-vent length 17–20 mm) best hearing sensitivities were measured in the 2.4–2.8 kHz range, whereas optimal hearing sensitivity of older adults (body mass 18–90 gm; snout-vent length 57–100 mm) ranged from 1.0 to 1.2 kHz. Middle ear volumes reconstructed from serial sections showed approximate volume of 0.002 cc and 0.04–0.07 cc in newly metamorphosed and older frogs, respectively. This inverse frequency–volume relationship is consistent with the properties of an acoustic resonator indicating that differences in best hearing sensitivity are at least in part correlated to variation in middle ear volumes for airborne sounds. These results are consistent with peak frequency vibrational velocity profiles of Xenopus tympanic disk that have been shown to be dependent on underlying middle ear volumes and corroborate the occurrence of peak amplitudes of otoacoustic emissions in the 1.0–1.2 kHz region in adult Xenopus frogs.     

Effects of Boat Engine Noise on the Auditory Sensitivity of the Fathead Minnow, Pimephales promelas

Fishes are constantly exposed to various sources of noise in their underwater acoustic environment. Many of these sounds are from anthropogenic sources, especially engines of boats. Noise generated from a small boat with a 55 horsepower outboard motor was played back to fathead minnows, Pimephales promelas, for 2 h at 142 dB (re: 1 Pa), and auditory thresholds were measured using the auditory brainstem response (ABR) technique. The results demonstrate that boat engine noise significantly elevate a fish's auditory threshold at 1 kHz (7.8 dB), 1.5 kHz (13.5 dB), and 2.0 kHz (10.5 dB), the most sensitive hearing range of this species. Such a short duration of noise exposure leads to significant changes in hearing capability, and implies that man-made noise generated from boat engines can have far reaching environmental impacts on fishes.     

Sound localization by the bottlenose porpoise Tursiops truncatus.

1. Sound localization was measured behaviourally for the Atlantic bottlenose porpoise (Tursiops truncatus) using a wide range of pure tone pulses as well as clicks simulating the species echolocation click. 2. Measurements of the minimum audible angle (MAA) on the horizontal plane give localization discrimination thresholds of between 2 and 3 degrees for sounds from 20 to 90 kHz and thresholds from 2-8 to 4 degrees at 6, 10 and 100 kHz. With the azimuth of the animal changed relative to the speakers the MAAs were 1-3-1-5 degrees at an azimuth of 15 degrees and about 5 degrees for an azimuth of 30 degrees. 3. MAAs to clicks were 0-7-0-8 degrees. 4. The animal was able to do almost as well in determining the position of vertical sound sources as it could for horizontal localization. 5. The data indicate that at low frequencies the animal may have been localizing by using the region around the external auditory meatus as a detector, but at frequencies about 20 kHz it is likely that the animal was detecting sounds through the lateral sides of the lower jaw. 6. Above 20 kHz, it is likely that the animal was localizing using binaural intensity cues. 7. Our data support evidence that the lower jaw is an important channel for sound detection in Tursiops.     

Auditory temporal resolution and evoked responses to pulsed sounds for the Yangtze finless porpoises (<Emphasis Type="Italic">Neophocaena phocaenoides asiaeorientalis</Emphasis>)

Temporal cues are important for some forms of auditory processing, such as echolocation. Among odontocetes (toothed whales, dolphins, and porpoises), it has been suggested that porpoises may have temporal processing abilities which differ from other odontocetes because of their relatively narrow auditory filters and longer duration echolocation signals. This study examined auditory temporal resolution in two Yangtze finless porpoises (Neophocaena phocaenoides asiaeorientalis) using auditory evoked potentials (AEPs) to measure: (a) rate following responses and modulation rate transfer function for 100 kHz centered pulse sounds and (b) hearing thresholds and response amplitudes generated by individual pulses of different durations. The animals followed pulses well at modulation rates up to 1,250 Hz, after which response amplitudes declined until extinguished beyond 2,500 Hz. The subjects had significantly better hearing thresholds for longer, narrower-band pulses similar to porpoise echolocation signals compared to brief, broadband sounds resembling dolphin clicks. Results indicate that the Yangtze finless porpoise follows individual acoustic signals at rates similar to other odontocetes tested. Relatively good sensitivity for longer duration, narrow-band signals suggests that finless porpoise hearing is well suited to detect their unique echolocation signals.     

Hearing in honeybees: operant conditioning and spontaneous reactions to airborne sound

Summary Airborne sound signals emitted by dancing bees (Apis mellifera) play an essential role in the bees' dance communication. It has been shown earlier that bees can learn to respond to airborne sounds in an aversive conditioning paradigm. Here we present a new training paradigm. A Y-choice situation was used to determine the frequency range and amplitude thresholds of hearing in bees. In addition, spontaneous reactions of bees to airborne sound were observed and used to determine thresholds of hearing. Both methods revealed that bees are able to detect sound frequencies up to about 500 Hz. The hearing threshold is 100–300 mm/s peak-to-peak velocity and is roughly constant over the range of detectable frequencies. The amplitude of the signals emitted in the dance language is 5 to 10 times higher, so we can conclude that bees can easily detect the dance sounds.     

Sound reception in marine mammals depending on sound parameters and conduction pathways

The interaction of complex sounds with the body tissues of Black Sea dolphin (Tursiops truncatus) was studied by the method of instrumental conditioned reflexes with food reinforcement. The thresholds of detecting underwater acoustic signals of different frequencies for dolphin and northern fur seal (Callorhinus ursinus) were measured as a function of pulse duration under conditions of full and partial (head above water) submergence of animals into water. It was found that sound conduction through dolphin tissues was more effective than that in a northern fur seal in a wide frequency range. Presumably, the process of sound propagation in dolphin is accompanied by changes in the amplitude-frequency structure of broad-band sounds. The temporal summation in dolphin hearing was observed at all frequencies under conditions of full and partial submergence, whereas in northern fur seal it was nearly absent at a frequency of 5 kHz under the conditions of head lifting above water.     

Temporal summation under masking conditions and speech recognition

Temporal summation was estimated by measuring the detection thresholds for pulses with durations of 1–50 ms in the presence of noise maskers. The purpose of the study was to examine the effects of the spectral profiles and intensities of noise maskers on temporal summation, to investigate the appearance of signs of peripheral processing of pulses with various frequency-time structures in auditory responses, and to test the opportunity to use temporal summation for speech recognition. The central frequencies of pulses and maskers were similar. The maskers had ripple structures of the amplitude spectra of two types. In some maskers, the central frequencies coincided with the spectrum humps, whereas in other maskers, they coincided with spectrum dip (so-called on- and off-maskers). When the auditory system differentiated the masker humps, then the difference between the thresholds of recognition of the stimuli presented together with each of two types of maskers was not equal to zero. The assessment of temporal summation and the difference of the thresholds of pulse recognition under conditions of the presentation of the on- and off-maskers allowed us to make a conclusion on auditory sensitivity and the resolution of the spectral structure of maskers or frequency selectivity during presentation of pulses of various durations in local frequency areas. In order to estimate the effect of the dynamic properties of hearing on sensitivity and frequency selectivity, we changed the intensity of maskers. We measured temporal summation under the conditions of the presentation of on- and off-maskers of various intensities in two frequency ranges (2 and 4 kHz) in four subjects with normal hearing and one person with age-related hearing impairments who complained of a decrease in speech recognition under noise conditions. Pulses shorter than 10 ms were considered as simple models of consonant sounds, whereas tone pulses longer than 10 ms were considered as simple models of vowel sounds. In subjects with normal hearing in the range of moderate masker intensities, we observed an enhancement of temporal summation when the short pulses or consonant sounds were presented and an improvement of the resolution of the broken structure of masker spectra when the short and tone pulses, i.e., consonant and vowel sounds, were presented. We supposed that the enhancement of the summation was related to the refractoriness of the fibers of the auditory nerve. In the range of 4 kHz, the subject with age-related hearing impairments did not recognize the ripple structure of the maskers in the presence of the short pulses or consonant sounds. We supposed that these impairments were caused by abnormal synchronization of the responses of the auditory nerve fibers induced by the pulses, and this resulted in a decrease in speech recognition.     

Ontogenetic development of weberian ossicles and hearing abilities in the African bullhead catfish

Background

The Weberian apparatus of otophysine fishes facilitates sound transmission from the swimbladder to the inner ear to increase hearing sensitivity. It has been of great interest to biologists since the 19^th century. No studies, however, are available on the development of the Weberian ossicles and its effect on the development of hearing in catfishes.

Methodology/Principal Findings

We investigated the development of the Weberian apparatus and auditory sensitivity in the catfish Lophiobagrus cyclurus. Specimens from 11.3 mm to 85.5 mm in standard length were studied. Morphology was assessed using sectioning, histology, and X-ray computed tomography, along with 3D reconstruction. Hearing thresholds were measured utilizing the auditory evoked potentials recording technique. Weberian ossicles and interossicular ligaments were fully developed in all stages investigated except in the smallest size group. In the smallest catfish, the intercalarium and the interossicular ligaments were still missing and the tripus was not yet fully developed. Smallest juveniles revealed lowest auditory sensitivity and were unable to detect frequencies higher than 2 or 3 kHz; sensitivity increased in larger specimens by up to 40 dB, and frequency detection up to 6 kHz. In the size groups capable of perceiving frequencies up to 6 kHz, larger individuals had better hearing abilities at low frequencies (0.05–2 kHz), whereas smaller individuals showed better hearing at the highest frequencies (4–6 kHz).

Conclusions/Significance

Our data indicate that the ability of otophysine fish to detect sounds at low levels and high frequencies largely depends on the development of the Weberian apparatus. A significant increase in auditory sensitivity was observed as soon as all Weberian ossicles and interossicular ligaments are present and the chain for transmitting sounds from the swimbladder to the inner ear is complete. This contrasts with findings in another otophysine, the zebrafish, where no threshold changes have been observed.     

单频刺激声稳态诱发反应的可靠性研究

目的:通过测试正常听力青年男女的听觉多频稳态诱发反应ASSR和单频刺激声稳态诱发反应探求单频刺激声稳态诱发反应的可靠性。方法:选取32名64耳听力正常的青年人作为受试者,对其进行纯音听阈、ASSR及四个0.5、1、2、4k Hz单频刺激声稳态诱发反应阈值测试,并记录0.5、1、2和4k Hz四个频率纯音阈值及ASSR及四个单频刺激声稳态诱发反应阈值。结果:ASSR在0.5、1、2和4k Hz四个频率的反应阈值与纯音听阈阈值相关性系数分别为0.64、0.81、0.79、0.85;0.5k Hz单频刺激声稳态诱发反应阈值与ASSR阈值具有明显统计学差异,其余3个单频刺激声稳态诱发反应阈值与ASSR阈值没有统计学差异,0.5k Hz单频刺激声稳态诱发反应阈值与纯音听阈阈值相关性系数为0.81。结论:ASSR阈值与纯音听阈具有较好的相关性,0.5k Hz单频刺激声稳态诱发反应可以提高0.5k Hz ASSR阈值与纯音听阈的相关性。     

Evoked potentials of the auditory cortex of the porpoise,Phocoena phocoena

Summary Evoked potential (EP) recordings in the auditory cortex of the porpoise,Phocoena phocoena, were used to obtain data characterizing the auditory perception of this dolphin. The frequency threshold curves showed that the lowest EP thresholds were within 120–130 kHz. An additional sensitivity peak was observed between 20 and 30 kHz. The minimal EP threshold to noise burst was 3·10^–4–10^/s-3 Pa. The threshold for response to modulations in sound intensity was below 0.5 dB and about 0.1% for frequency modulations. Special attention was paid to the dependence of the auditory cortex EP on the temporal parameters of the acoustic stimuli: sound burst duration, rise time, and repetition rate. The data indicate that the porpoise auditory cortex is adapted to detect ultrasonic, brief, fast rising, and closely spaced sounds like echolocating clicks.Abbreviation EP evoked potential