Broadband Click Research Articles

Arctiid moths and bat echolocation: broad-band clicks interfere with neural responses to auditory stimuli in the nuclei of the lateral lemniscus of the big brown bat.

Clicks emitted by arctiid moths interfere with the ranging ability of echolocating bats. To identify possible neural correlates of this interference, we recorded responses of single units in the nuclei of the lateral lemniscus to combinations of a broad-band click and a test signal (pure tones or frequency-modulated sweeps). In 77% of 87 units tested, clicks interfered with neural responses to the test stimuli. The interference fell into two categories: latency ambiguity and suppression. Units showing latency ambiguity responded to both the click and the test signal. However, when the click occurred within a window of approximately 3 ms before the onset of the test signal, the latency of the response to the test signal was affected. Units that were suppressed did not respond to clicks. Nevertheless, when a click was presented immediately before or simultaneously with a test signal, the response to the test signal was eliminated. Both types of units were found throughout the lateral lemniscus except for the columnar division of the ventral nucleus, where all units tested exhibited latency ambiguity. There is a close match between the single unit data and previous studies of range difference discrimination in the presence of clicks.

Temporary threshold shifts induced by low-pass and high-pass filtered noises in fetal sheep in utero

Auditory brainstem responses (ABRs) were obtained from nine late gestational age fetal sheep in utero before and after a 16-h exposure to low-pass (cut-off frequency 1.0 kHz) and high-pass (cut-off frequency 1.0 kHz) noises (approximately 120 dB sound pressure level, recorded in air). Bone-conduction ABRs were elicited by broadband clicks and 0.5, 1.0 and 2.0 kHz tone bursts. Following low-pass noise exposure, ABR thresholds and wave IV latencies increased significantly for 0.5 and 1.0 kHz tone bursts. The high-pass noise exposure produced significant shifts in ABR thresholds and wave IV latencies only for the 1.0 kHz tone bursts. These findings confirm previous reports of low-frequency sound transmission into the fetal inner ear.

Medial Olivocochlear Efferent System in Humans Studied With Amplitude-Modulated Tones

Evoked otoacoustic emissions (EOAEs) are assumed to be generated by outer hair cells (OHCs). It is now generally accepted that EOAEs represent a means of functional exploration of the active micromechanical properties of OHCs. Efferent fibers of the medial olivocochlear system (MOCS) are connected along the sides and the bases of OHCs. Some studies have shown that a suppression effect on EOAE amplitude is induced by the MOCS neurons during contralateral stimulation, presumably by modification of OHC motility. The contralateral acoustic stimuli used in experiments on the EOAE suppression effect have consisted mainly of sounds without a slow temporal fluctuation in their envelopes (broad-band noise, narrow-band noise, pure tones, or clicks). To elucidate further the parameters of MOCS activation, in the present study we looked at the contralateral suppression effect of amplitude-modulated (AM) tones. The results showed that EOAE amplitude was reduced with AM tones compared with no contralateral acoustic stimulation. The suppression effect mainly depended on three parameters. 1) Contralateral stimulation intensity: EOAE suppression occurred only with intensities > or = 40 dB SL. 2) The greater the modulation depth, the greater the suppression effect: statistical analysis showed a significant effect for 75 and 100% modulation depth. 3) The 100- and 140-Hz modulation frequencies gave the greatest suppression effect for 100 and 75% modulation depths. The suppression effect was frequency specific. The greatest decreases were observed when the carrier frequency of the contralateral AM tone was close to the frequency of the EOAE under study, i.e., 1 and 2 kHz. Acoustic cross talk and middle ear effects, which cannot be completely excluded, are discussed. However, the demonstrated frequency specificity of the EOAE suppression effect, together with observed presence of contralateral EOAE suppression in patients without stapedial reflex and the very weak intensities used (i.e., below acoustic reflex threshold), suggested that it was unlikely that the observed effects were due merely to middle ear reflexes. Our results confirm further the contralateral suppression effect on human cochlea mechanisms and show that the suppression effect can be influenced by amplitude modulations of the suppressor, characteristic of sounds in the environment.

Energy detection and temporal integration in the noctuid A1 auditory receptor

The temporal integration of the A1 auditory receptor of two species of noctuid moths (Lepidoptera, Noctuidae) was investigated. Tympanal nerve spikes were recorded while stimulating the ear with broad band clicks. Thresholds were measured for single clicks, pairs of clicks with a separation of 1–20 ms, and trains of up to 8 clicks at separations of 1–2 ms. The average threshold for single clicks was 52.9 dB peSPL (SD 1.7 dB, n = 40) for Noctua pronuba and 50.1 dB peSPL (SD 4.0 dB, n = 27) for Spodoptera littoralis. The thresholds for double clicks with a 1 ms separation were lower than the thresholds for single clicks. The difference decreased as the separation between the clicks was increased. The results were fully consistent with an energy detector model (a leaky integrator with an exponential decay) with a time constant of about 4 ms. The results are compared to previously published results with pure tone intensity/duration trading. A common underlying mechanism is suggested, based on the passive electric properties of the receptor cell membrane. It is suggested, that the time constant revealed in the present study characterizes auditory receptors in general, and is related to the short time constants in vertebrate audition.

Audiogram Construction Using Frequency-Specific Auditory Brainstem Response (ABR) Thresholds

Brainstem evoked response audiometry (ABR) permits auditory pathway assessment without the need for voluntary response. Brainstem responses are unaffected by attention, drugs, and most other confounding conditions. Consequently, if ABR could be used to determine hearing threshold in the speech frequencies, it would have great value for patients who are unable or unwilling to respond accurately during behavioral audiometric testing. Utilizing broad band clicks, one can only estimate hearing sensitivity in the frequency range of 2,000 to 4,000 Hz. This is inadequate for medical or legal purposes in which hearing in the speech frequencies must be assessed. Consequently, we have developed a modified ABR technique that permits a more accurate determination of hearing threshold at 500, 1,000, 2,000 and 3,000 Hz, as illustrated in tests on 27 normal ears. This technique has great potential value for neonatal and mentally handicapped populations, as well as for individuals involved in hearing loss litigation.

Signal strength, timing, and self-deafening: the evolution of echolocation in bats

We propose that the ancestors of bats were small, nocturnal, sylvatic gliders that used echolocation for general orientation. Their echolocation calls were short, low intensity, broadband clicks, which translated into a very short operational range. In the lineage that gave rise to bats, a switch to stronger, tonal signals permitted the use of echolocation to detect, track, and assess flying insects in subcanopy settings. We propose that these animals hunted from perches and used echolocation to detect, track, and assess flying insects, which they attacked while gliding. In this way, the perfection of echolocation for hunting preceded the appearance of flapping flight, which marked the emergence of bats. Flapping flight had appeared by the Eocene when at least eight families are known from the fossil record. Stronger signals and adaptations to minimize self-deafening were central to the perfection of echolocation for locating flying prey. Echolocation constituted a key innovation that permitted the evolution and radiation of bats. At the same time, however, its short effective range imposed a major constraint on the size of bats. This constraint is associated with flight speed and the very small time intervals from detection of, and contact with a flying target. Gleaning and high duty cycle echolocation are two derived approaches to hunting prey in cluttered situations, places where echoes from background and other objects arrive before or at the same time as echoes from prey. Both had appeared by the Eocene.

Coats Electrode를 이용한 고막외적 유도법에 의한 전기와우도

Electrocochleography(ECoG) is a method of recording the stimulus-related potentials of the cochlear and auditory nerve. Clinically the electrodes used for ECoG recording in human are classified as invasive or noninvasive depending on whether or not they penetrate the ear drum. Non-invasive extratympanic ECoG was performed on 46 normal hearing ears and 40 ears with positive recruitment of other origin than endolymphatic hydrops with Coats electrode. We have measured the normal value of latency and amplitude of SP, AP and SP/AP ratio at 87dB HL of alternating broad band & IK, 4K, 8KHz narrow band click sound and compared the latency and amplitude on normal hearing ears and cochlear learing ears at same condition. We also compared the amplitiude and the latency of SP, AP and SP/AP with transtympanic and extratympanic ECoG in normal hearing ear. The results were as follows: There were no significant different latency and amplitude of SP and AP according to frequency of click stimuli. And maxiuni value of amplitude with minium SD was obtained at broad band click. In normal hearing ears, the amplitude of SP and that of AP were 0.58±0.44 and 4.14±0J4respectively and the latencies of SP and AP were 1.09±0.14msec and 1.66±0.11msec respecitvley at 87dB HL broad band click. There were significant decreased amplitudes of SP and AP of cochlear hearing loss ears than normal hearing ears at each frequencies(p<0.05). There were significant prolonged latencies of SP and AP of cochlear hearing loss ears than normal hearing ears at each frequencies. Although the amplitudes of SP and AP with noninvasive extratympanic ECoG were 1/6 to 1/7 of that with invasive ttranstympanic ECoG, SP/AP with extratympanic and transtympanic ECoG of normal hearing ears were nearly equal and about 0.46. Authors concluded that extratympanic ECoG recording with Coats electrode is enough diagnostic tool for inner ear disease.

The ototoxicity of 3,3′-iminodipropionitrile: Functional and morphological evidence of cochlear damage

Previous reports have suggested that IDPN may be ototoxic (Wolff et al., 1977; Crofton and Knight, 1991). The purpose of this research was to investigate the ototoxicity of IDPN using behavioral, physiological and morphological approaches. Three groups of adult rats were exposed to IDPN (0–400 mg/kg/day) for three consecutive days. In the first group, at 9–10 weeks post-exposure, thresholds for hearing of 5.3- and 38-kHz filtered clicks were measured electrophysiologically and brainstem auditory evoked responses (BAERs) were also recorded to a suprathreshold broadband click stimulus. A second set of animals was tested at 9 weeks for behavioral hearing thresholds (0.5- to 40-kHz tones) and at 11–12 weeks post-exposure for BAER thresholds (5- to 80-kHz filtered clicks). A third group of animals was exposed (as above), and killed at 12–14 weeks post-exposure for histological assessment. Kanamycin sulfate was used as a positive control for high-frequency selective hearing loss. Surface preparations of the organ of Corti were prepared in order to assess hair cells, and mid-modiolar sections of the cochlea were used to examine Rosenthal's canal and the stria vascularis. Functional data demonstrate a broad-spectrum hearing loss ranging from 0.5 kHz (30 dB deficit) to 80 kHz (40 dB deficit), as compared to a hearing deficit in kanamycin-exposed animals that was only apparent at frequencies greater than 5 kHz. Surface preparations revealed IDPN-induced hair cell loss in all turns of the organ of Corti, with a basal-to-apical gradient (more damage in the basal turns) at the lower dosages. At higher dosages there was complete destruction of the organ of Corti. There was also a dosage-related loss of spiral ganglion cells in all turns of the cochlea, again with a basal-to-apical gradient at the lower dosages. These data demonstrate that IDPN exposure in the rat results in extensive hearing loss and loss of neural structures in the cochlea.

Brainstem Auditory Evoked Potentials

Brainstem auditory evoked potentials (BAEPs) have obtained widespread clinical application in assessing neurologic and audiologic problems. Seven waves (I-VII) are usually recorded in the first 10 ms following broad-band and high-intensity clicks. Latencies of waves I, III, and V, interpeak latencies of I-III, III-V, and I-V, and the amplitude ratio of wave V to wave I are common parameters evaluated for assessing clinically relevant abnormalities of BAEPs. Usually two-channel recordings are obtained: vertex (Cz) to ipsilateral ear and Cz to contralateral earlobe derivation. Evaluating different components in the two derivations helps their identification, particularly when the BAEPs are abnormal. Several technical and subject-related factors affect the amplitude and latencies of BAEP components besides lesions and dysfunctions involving the peripheral auditory structures and brainstem auditory pathways. BAEPs have maximal clinical utility in evaluating comatose patients, in patients with suspected demyelinating disorders, posterior fossa tumors, or in audiologic evaluation, especially in infants. They are also used for intraoperative monitoring of eighth-nerve and brainstem function during different types of posterior fossa surgery.

Binaural masking and lateralization of click trains with alternating interaural time delays

Broadband click trains were used to investigate the effect of onset and ongoing interaural time delays (ITDs) on lateralization and binaural masking. Within a train, successive click pairs had ITDs that were either identical or alternated between two values. The interclick interval was 2 ms and the total duration of each train was 250 ms. Perceived intracranial position of the signals was estimated using an acoustic pointer. Detection thresholds for the same trains were obtained in the presence of a continuous white noise masker with a fixed interaural delay. It was found that lateralization generally followed the ITD of the very first click pair in the train. Masked thresholds were dependent upon the proximity of one or both signal ITDs to the masker ITD, but were independent of the perceived lateral position of the signal relative to that of the masker. These results suggest that while the onset ITD may dominate lateralization for click trains, it has no influence on masked binaural detection of the same signals. [Work supported by NIDCD Grant No. DC01625.]

Effects of hyperthermia on the auditory-evoked brainstem responses in mice.

This study investigated the effects of increased body temperature on the latencies and amplitudes of the auditory-evoked brainstem response (ABR) in mice. Six eleven-week-old male CBA/CaJ mice were anesthetized with pentobarbital and screened for normal hearing. Hyperthermia was induced by placing the animal in a thermostatically controlled chamber; a thermistor connected to a digital thermometer measured the rectal temperature. ABRs were evoked with broad-band clicks presented at repetition rates of 21.1/s and 61.1/s. The latencies and amplitudes of waves I-V were measured at 1-degree and/or 0.5-degree intervals between 37 and 42 degrees C. Temperature elevation between 37 and 41 degrees C shortened the latencies of all the ABR waves, the effect being linear and cumulative across the time window. Change in this trend occurred between 41 and 42 degrees C, whereby the latencies of all the waves stabilized or showed minimal prolongation. Amplitudes of the most robust waves I and II showed a trend similar to the latencies, whereas the later waves showed erratic and uninterpretable changes. These findings in the mouse may be indicative of the physiological limit of thermal tolerance and as such may be regarded as a premonitory signal of permanent damage.

Origin of the click-evoked binaural interaction potential, β, of humans

The human click-evoked binaural difference waveform has as its most prominent feature the peak, β, which has been shown to be related to binaural perception. In normal human subjects, we investigated the effect upon β of (1) delivering the clicks in the presence of high passed masking noise (4000 Hz cut-off) and (2) reversing click polarity. In the presence of the masker, little activity occurs at the time the click-evoked β would be expected. No significant change in β latency occurs when the click polarity is inverted. We conclude that β is principally due to the high-frequency components of the broad band click, so that it is through the activity in high characteristic frequency auditory nerve fibers that click-evoked β is generated. Because the medial superior olive is the major nucleus of the human superior olivary complex, our results suggest that β is possibly generated by the high-frequency cells of the medial superior olive.

Assessment of cisplatin-induced ototoxicity using derived-band ABRs

Ototoxicity is an adverse side effect of numerous therapeutic agents (aminoglycoside antibiotics, blood chelating agents, diuretics and oncologic drugs) used in treatment of both adult and pediatric patients. Recently, there has been increasing interest in using the auditory brainstem response (ABR) to detect both short-term effects of ototoxicity in adults and long-term effects of drug administration on neonates and children. Since click ABRs have relatively poor frequency selectivity they best approximate the pure-tone hearing threshold in the 2000–4000 Hz frequency range. Hearing loss above or below that frequency range can be present without producing significant abnormalities in the ABR waveform parameters. Frequency-specific ABRs can be obtained using the derived response technique. The purpose of this study was to investigate early cisplatin ototoxicity using both the broadband click and derived ABR and to monitor progressive hearing loss with repeated drug trials in 18 patients studied over a 2-year period. ABRs were obtained serially prior to and following intravenous administration of cisplatin. Derived ABRs were found to be more sensitive than broadband click ABR in detecting early high-frequency hearing loss. For click ABRs, the cumulative dosage of cisplatin at age of ABR examination was correlated with hearing loss in only those patients under 3 years of age. No significant correlation was found between cumulative cisplatin dosage when tested and degree of hearing loss in those patients over 3 years of age.

Complex and Pure-Tone Signals in the Evaluation of Hearing-Aid Characteristics

In recent years, a number of commercially available systems have been developed to analyze the electroacoustic characteristics of hearing aids. In addition to pure-tone signals, these systems often use a wide variety of complex signals such as broadband noise, clicks, and multitonal complexes. In this paper, a number of practical and theoretical issues concerning the use of pure-tone and complex signals in the evaluation of hearing-aid characteristics are described. The circumstances under which discrepancies in estimated gain and maximum output might occur using these two types of signals are described and the clinical implications of these differences are discussed.

Late components in the compound action potentials (CAP) recorded from the intracranial portion of the human eighth nerve

The compound action potential (CAP) that can be recorded from the exposed intracranial portion of the eighth nerve in man to stimulation with broadband clicks of about 100 dB Pe SPL normally has an initial (small) positivity followed by a sharp negative peak with a latency of about 3 to 3.5 ms. The negative peak is usually followed by another positive-negative deflection with a latency of about 4 ms. Usually, no stimulus-related potential can be discerned at latencies longer than 5 ms. However, in a few patients we found a series of waves that occurred between 4 and 12 ms after the stimulation. The polarity of these waves reversed precisely (180° phase shift) when the polarity of the sound was reversed. Thus, these waves appeared clearly when the responses to clicks of opposite polarity were subtracted. These late waves were quasiperiodic with intervals between 1 and 2 ms. The waveform and duration differed between patients, but were remarkably constant in each patient. The timing of these late peaks was nearly independent of the stimulus intensity in the range studied (between 105 and 70 dB Pe SPL); in this respect the late waves differ fundamentally from the initial peaks, which showed a monotone decrease in latency with increasing stimulus intensity over this intensity range. Although the origin of these late waves is not known, the similarities between these waves and stimulated otoacoustic emissions indicate that the late waves may be the result of active cochlear processes similar to those that produce the cochlear echo.

Responses from the exposed human auditory nerve to pseudorandom noise

Whole-nerve responses to lowpass-filtered noise (2.5 kHz) and broadband click stimuli were recorded from the exposed intracranial portion of the eighth nerve in patients with normal hearing who were undergoing neurosurgical operations to relieve vascular compression of cranial nerves V, VII, and VIII. Cross-correlograms between the response and the noise showed a large degree of individual variation. When noise of 95 dB SPL was used, the correlograms in some patients had a large peak that represented a positive correlation between a negative nerve potential and the rarefaction phase of the sound and that peak could usually be identified at a delay that was close to the latency of the main negative peak in the response to high-intensity broadband click sounds (3.0–3.5 ms). The amplitude of these components decreased when the sound intensity was decreased, and, at stimulus intensities below 80 dB, the correlograms became dominated by components at longer delays. In other patients, peaks of a similar amplitude appeared in the cross-correlograms between delays of 2 and 12 ms in the entire range of sound intensities that were studied (65–105 dB SPL). In all patients the location of the peaks was little affected by the stimulus intensity in the range studied. All reproducible peaks that appeared at delays longer than 2.8 ms shifted towards longer delays when the recording electrode was moved from a location near the porus acusticus to a more central location (near the brainstem) on the exposed intracranial portion of the eighth nerve, indicating that components at longer delays than 2.8 ms result from propagated neural activity in the auditory nerve. It is assumed on the basis of the results that these correlograms are measures of phase-locking of neural activity to a complex stimulus sound (noise).

Detection of sonar signals in the presence of pulses of masking noise by the echolocating bat,Eptesicus fuscus

Two big brown bats (Eptesicus fuscus) were trained to report the presence or absence of a virtual sonar target. The bats' sensitivity to transient masking was investigated by adding 5 ms pulses of white noise delayed from 0 to 16 ms relative to the target echo. When signal and masker occurred simultaneously, the bats required a signal energy to noise spectrum level ratio of 35 dB for 50% probability of detection. When the masker was delayed by 2 ms or more there was no significant masking and echo energy could be reduced by 30 dB for the same probability of detection. The average duration of the most energetic sonar signal of each trial was measured to be 1.7 ms and 2.4 ms for the two bats, but a simple relation between detection performance and pulse duration was not found. In a different experiment the masking noise pulses coincided with the echo, and the duration of the masker was varied from 2 to 37.5 ms. The duration of the masker had little or no effect on the probability of detection. The findings are consistent with an aural integration time constant of about 2 ms, which is comparable to the duration of the cries. This is an order of magnitude less than found in backward masking experiments with humans and may be an adaptation to the special constraints of echolocation. The short time of sensitivity to masking may indicate that the broad band clicks of arctiid moths produced as a countermeasure to bat predation are unlikely to function by masking the echo of the moth.

Instrumentation for dolphin echolocation experiments

The use of personal computers has contributed significantly in dolphin echolocation research by providing an inexpensive instrument to measure echolocation signals, monitor and control experimental devices, and to store data. Dolphins typically emit short duration (50–100 μs), broadband click signals with repetition rates that can vary from tens of clicks per second to several hundred clicks per second. In this paper, three electronic measurement devices used with Apple II computers in dolphin echolocation experiments will be discussed. The first device measures the number of clicks emitted, the intervals between clicks, the peak‐to‐peak amplitude of each click, and the time of activation of various switches. The second device measures the frequency spectrum (between 30 and 135 kHz) of each emitted click signal in real time, with a resolution of 15 kHz. The third device is a phantom electronic target simulator that digitizes each emitted click and then retransmits the click signal under control of the computer. The development of these three devices has been a process of evolution in sophistication over a period of several years of dolphin echolocation research conducted at the Naval Ocean Systems Center.

Structural effects of short term and chronic extracochlear electrical stimulation on the guinea pig spiral organ

To assess the effects of extracochlear electrical stimulation on cochlear structure, guinea pigs were implanted and stimulated with single middle ear electrodes either at round window or promontory sites, and their cochleae examined by transmission electron microscopy. Implanted but unstimulated, or unimplanted control animals were examined in the same way. Alternating current stimulation at the promontory for 2 h at 150 Hz, 500 μA, caused outer hair cell efferent endings to become dense and vacuolated, but no hair cells were damaged. With direct current stimulation at 500 μA for 2 h the basal regions of the stimulated cochlea were badly damaged and many outer hair cells lysed. Long term (up to 1200 h) round window stimulation at 100 or 141 Hz, 15–91 μA rms. did not cause cell death or inner hair cell damage, but basal outer hair cells and their efferent endings were badly affected in both ipsilateral and contralateral cochleae. The compound action potential of the auditory evoked response to broad band click stimuli was not altered by chronic electrical stimulation. It is concluded that chronic stimulation with the parameters used does not threaten cochlear survival, and it is proposed that the bilateral structural changes induced by chronic stimulation are caused by excessive activation of the cochlear efferent pathways.

Effect of Click Spectrum and Polarity on Round Window N1N2Response in the Rat1

The effect of the duration of click stimuli on the compound action potential recorded from the round window in the rat and the effect of low-pass filtering of short click sounds were studied. Thus the intensity functions of the round window N1 potential have a two-segment course and there is a difference in the response to rarefaction and condensation clicks, depending upon the content of low-frequency components in the click stimulus. The intensity function of the rat's response to broadband clicks does not show the same two-segment course as has been reported in experiments in other animals, and there is little difference between the response to condensation clicks and that to rarefaction clicks in this animal. However, when the duration of the click is increased or when broadband clicks are subjected to low-pass filtering, the intensity functions in response to condensation clicks do show a change in course, while the response to rarefaction clicks remains essentially unchanged. A similar change in the response to a broadband click can be induced by adding a low-pass-filtered click to the broadband click. The response to such a combination is not only a linear summation of the neural response to the individual components of the stimuli and the cochlear microphonics, but the low-frequency components that are added also affect the response to the broadband click, mainly by reducing the amplitude of the response.