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At least 775 records · Page 43Linked to original sources
PubMed2004

Validation of a new system of tracheal sound analysis for the diagnosis of sleep apnea-hypopnea syndrome.

STUDY OBJECTIVES: To evaluate the validity of a novel method of using tracheal sound analysis for the diagnosis of sleep apnea-hypopnea syndrome. DESIGN: Retrospective analysis in consecutive patients. SETTING: A sleep clinic in a general hospital. PATIENTS: A total of 383 patients who were referred for suspected sleep apnea-hypopnea syndrome and underwent diagnostic polysomnography with sufficient quality. INTERVENTIONS: N/A. MEASUREMENTS AND RESULTS: Ordinary polysomnography with simultaneous tracheal sound recording was performed. The apnea-hypopnea index (AHI) was calculated as the number of apnea and hypopnea events per hour of sleep. Tracheal sounds were digitized and recorded as power spectra. An automated computer program detected transient falls (TS-dip) in the time series of moving average of the logarithmic power of tracheal sound. We defined the tracheal sound-respiratory disturbance index (TS-RDI) as the number of TS-dips per hour of examination. We also calculated the oxygen desaturation index (the number of SaO2 dips of at least 4% per hour of examination). The TS-RDI highly correlated with AHI (r = 0.93). The mean (+/- SD) difference between the TS-RDI and AHI was -8.4 +/- 10.4. The diagnostic sensitivity and specificity of the TS-RDI when the same cutoff value was used as for AHI were 93% and 67% for the AHI cutoff value of 5 and 79% and 95% for the AHI cutoff value of 15. The agreement between the TS-RDI and AHI was better than that between the oxygen desaturation index and AHI. CONCLUSIONS: The fully automated tracheal sound analysis demonstrated a relatively high performance in the diagnosis of sleep apnea-hypopnea syndrome. We think that this method is useful for the portable monitoring of sleep apnea-hypopnea syndrome.

Adult↗
PubMed1999

The effect of halothane on the amplitude and frequency characteristics of heart sounds in children.

UNLABELLED: Although continuous auscultation has been used during surgery as a monitor of cardiac function for many years, the effect of anesthetics on heart sounds has never been quantified. We determined the root mean squared amplitude and frequency characteristics (peak frequency, spectral edge, and power ratios) of the first (S1) and second (S2) heart sounds in 19 healthy children during induction of anesthesia with halothane. In all patients, halothane decreased the amplitude of S1 (R2 = 0.87 +/- 0.12) and S2 (R2 = 0.66 +/- 0.33) and the high-frequency components (>80 Hz) of these sounds. These changes were clearly audible and preceded decreases in heart rate and blood pressure. The spectral edge decreased for S1 in 18 patients (R2 = 0.73 +/- 0.24) and for S2 in 13 patients (R2 = 0.58 +/- 0.25). Peak frequency did not change. The rapidity with which myocardial depression and its associated changes in heart sound characteristics occurred confirms that continuous auscultation of heart sounds is a useful clinical tool for hemodynamic monitoring of anesthetized infants and children. IMPLICATIONS: Heart sound characteristics can be used to monitor cardiac function during halothane anesthesia in children. The changes occur rapidly and precede noticeable changes in heart rate and blood pressure.

Age Factors↗
PubMed1996

Reduced order Kalman filtering for the enhancement of respiratory sounds.

In the processing and analysis of respiratory sounds, heart sounds present the main source of interference. This paper is concerned with the problem of cancellation of the heart sounds using a reduced-order Kalman filter (ROKF). To facilitate the estimation of the respiratory sounds, an autoregressive (AR) model is fitted to heart signal information present in the segments of the acquired signal which are free of respiratory sounds. The state-space equations necessary for the ROKF are then established considering the respiratory sound as a colored additive process in the observation equation. This scheme does not require a time alignment procedure as with the adaptive filtering-based schemes. The scheme is applied to several synthesized signals with different signal-to-interference ratios (SIR) and the results are presented.

Algorithms↗
PubMed2006

A robust method for estimating respiratory flow using tracheal sounds entropy.

The relationship between respiratory sounds and flow is of great interest for researchers and physicians due to its diagnostic potentials. Due to difficulties and inaccuracy of most of the flow measurement techniques, several researchers have attempted to estimate flow from respiratory sounds. However, all of the proposed methods heavily depend on the availability of different rates of flow for calibrating the model, which makes their use limited by a large degree. In this paper, a robust and novel method for estimating flow using entropy of the band pass filtered tracheal sounds is proposed. The proposed method is novel in terms of being independent of the flow rate chosen for calibration; it requires only one breath for calibration and can estimate any flow rate even out of the range of calibration flow. After removing the effects of heart sounds (which distort the low-frequency components of tracheal sounds) on the calculated entropy of the tracheal sounds, the performance of the method at different frequency ranges were investigated. Also, the performance of the proposed method was tested using 6 different segment sizes for entropy calculation and the best segment sizes during inspiration and expiration were found. The method was tested on data of 10 healthy subjects at five different flow rates. The overall estimation error was found to be 8.3 +/- 2.8% and 9.6 +/- 2.8% for inspiration and expiration phases, respectively.

Adult↗
PubMedDate not supplied

Evaluation of a low-cost 3D sound system for immersive virtual reality training systems.

Since Head Mounted Displays (HMD), datagloves, tracking systems, and powerful computer graphics resources are nowadays in an affordable price range, the usage of PC-based "Virtual Training Systems" becomes very attractive. However, due to the limited field of view of HMD devices, additional modalities have to be provided to benefit from 3D environments. A 3D sound simulation can improve the capabilities of VR systems dramatically. Unfortunately, realistic 3D sound simulations are expensive and demand a tremendous amount of computational power to calculate reverberation, occlusion, and obstruction effects. To use 3D sound in a PC-based training system as a way to direct and guide trainees to observe specific events in 3D space, a cheaper alternative has to be provided, so that a broader range of applications can take advantage of this modality. To address this issue, we focus in this paper on the evaluation of a low-cost 3D sound simulation that is capable of providing traceable 3D sound events. We describe our experimental system setup using conventional stereo headsets in combination with a tracked HMD device and present our results with regard to precision, speed, and used signal types for localizing simulated sound events in a virtual training environment.

Acoustics↗
PubMed2004

The bat head-related transfer function reveals binaural cues for sound localization in azimuth and elevation.

Directional properties of the sound transformation at the ear of four intact echolocating bats, Eptesicus fuscus, were investigated via measurements of the head-related transfer function (HRTF). Contributions of external ear structures to directional features of the transfer functions were examined by remeasuring the HRTF in the absence of the pinna and tragus. The investigation mainly focused on the interactions between the spatial and the spectral features in the bat HRTF. The pinna provides gain and shapes these features over a large frequency band (20-90 kHz), and the tragus contributes gain and directionality at the high frequencies (60 to 90 kHz). Analysis of the spatial and spectral characteristics of the bat HRTF reveals that both interaural level differences (ILD) and monaural spectral features are subject to changes in sound source azimuth and elevation. Consequently, localization cues for horizontal and vertical components of the sound source location interact. Availability of multiple cues about sound source azimuth and elevation should enhance information to support reliable sound localization. These findings stress the importance of the acoustic information received at the two ears for sound localization of sonar target position in both azimuth and elevation.

Animals↗
PubMed2000

Recognizing transient low-frequency whale sounds by spectrogram correlation.

A method is described for the automatic recognition of transient animal sounds. Automatic recognition can be used in wild animal research, including studies of behavior, population, and impact of anthropogenic noise. The method described here, spectrogram correlation, is well-suited to recognition of animal sounds consisting of tones and frequency sweeps. For a sound type of interest, a two-dimensional synthetic kernel is constructed and cross-correlated with a spectrogram of a recording, producing a recognition function--the likelihood at each point in time that the sound type was present. A threshold is applied to this function to obtain discrete detection events, instants at which the sound type of interest was likely to be present. An extension of this method handles the temporal variation commonly present in animal sounds. Spectrogram correlation was compared to three other methods that have been used for automatic call recognition: matched filters, neural networks, and hidden Markov models. The test data set consisted of bowhead whale (Balaena mysticetus) end notes from songs recorded in Alaska in 1986 and 1988. The method had a success rate of about 97.5% on this problem, and the comparison indicated that it could be especially useful for detecting a call type when relatively few (5-200) instances of the call type are known.

Animals↗
PubMed2005

Velocity and attenuation of sound in the isolated fetal lung as it is expanded with air.

We measured the velocity and attenuation of audible sound in the isolated lung of the near-term fetal sheep to test the hypothesis that the acoustic properties of the lung provide a measure of the volume of gas it contains. We introduced pseudorandom noise (bandwidth 70 Hz-7 kHz) to one side of the lung and recorded the noise transmitted to the surface immediately opposite, starting with the lung containing only fetal lung liquid and making measurements after stepwise inflation with air until a leak developed. The velocity of sound in the lung fell rapidly from 187 +/- 28.2 to 87 +/- 3.7 m/s as lung density fell from 0.93 +/- 0.01 to 0.75 +/- 0.01 g/ml (lung density = lung weight/gas volume plus lung tissue volume). For technical reasons, no estimate of velocity could be made before the first air injection. Thereafter, as lung density fell to 0.35 +/- 0.01 g/ml, there was a further decline in velocity to 69.6 +/- 4.6 m/s. High-frequency sound was attenuated as lung density decreased from 1.0 to 0.5 g/ml, with little change thereafter down to a density of 0.35 +/- 0.01 g/ml. We conclude that both the velocity of audible sound through the lung and the degree to which high-frequency sound is attenuated in the lung provide information on the degree of inflation of the isolated fetal lung, particularly at high lung densities. If studies of sound transmission through the lung in the intact organism were to confirm these findings, the acoustic properties of the lung could provide a means for monitoring lung aeration during mechanical ventilation of newborn infants.

Acoustic Stimulation↗
PubMed1990

Inspiratory and expiratory vesicular breath sounds.

Unfiltered breath sounds (NF) from the apical area of the heart, lung volume and ECG signals were recorded in 5 normal subjects. The signals were digitized and subjected to three methods of heart sound cancellation: 75-Hz high-pass filtering (75 HF), ECG-triggered blanking (BL) and adaptive filtering (AF). The sound signals were then subjected to the fast Fourier transform algorithm to obtain power spectra. Inspiratory and expiratory phase sounds of five breaths of each subject were analyzed separately. The inspiratory and expiratory sound power spectra were very similar and skewed slightly to the right, and therefore characterized by median frequencies. The differences between inspiratory and expiratory median frequencies were insignificant for NF: 42.90 +/- 2.03 (mean +/- SD) vs. 46.64 +/- 2.53 Hz (p greater than 0.1); for 75 HF: 106.43 +/- 10.27 vs. 118.22 +/- 6.30 Hz (p greater than 0.5); for BL: 44.46 +/- 3.33 vs. 66.73 +/- 2.93 Hz (p greater than 0.1), for AF: 49.72 +/- 5.68 vs. 79.20 +/- 13.07 Hz (p greater than 0.1). We conclude that the lack of significant differences suggests similar mechanisms and sites of production of inspiratory and expiratory vesicular breath sounds.

Adult↗
PubMed1996

Averaged and time-gated spectral analysis of respiratory sounds. Repeatability of spectral parameters in healthy men and in patients with fibrosing alveolitis.

STUDY OBJECTIVE: To obtain a basis for assessment of changes in breath sound spectra in patients with pulmonary diseases, short-term and day-to-day repeatability of spectral parameters was studied. DESIGN: Breath sounds were recorded simultaneously from the trachea and from the chest twice at an interval of 15 min (short-term repeatability) and of 1 to 3 days (day-to-day repeatability). During recordings, air flow at the mouth was controlled, the target inspiratory and expiratory peak flow being 1.25 L/s. Inspiratory and expiratory breath sound spectra were averaged over 7 to 10 successive respiratory cycles. The repeatability of sound intensity (RMS), frequency of maximum intensity (Fmax), and median frequency (F50) was analyzed with analysis of variance. PARTICIPANTS: Short-term repeatability was studied in 10 healthy nonsmoking men (age 25 to 44 years), and day-to-day repeatability was studied in 10 healthy nonsmoking men (age 23 to 41 years) and in 12 patients with clinically stable fibrosing alveolitis (age 35 to 82 years). RESULTS: Short-term coefficient of variation (CoV) of Fmax and F50 was 2.6 to 6.7% when recorded from the chest, and 6.2 to 8.7% when recorded from the trachea. Day-to-day CoV of Fmax and F50 in healthy subjects was 4.7 to 8.5% and 5.0 to 8.7% recorded from the chest or from the trachea, respectively. Inspiratory day-to-day variation in those parameters was higher in patients with fibrosing alveolitis. CoV of RMS was high, ranging from 18 to 47% in different subject groups and sampling situations. CONCLUSIONS: Repeatability of F50 of averaged flow-controlled lung sound spectra is good both in healthy subjects and in patients with fibrosing alveolitis. Thus, F50 of respiratory sound spectra may be useful in monitoring of changes induced by respiratory diseases and interventions. These results emphasize the importance of standardization of recording conditions and of analyzing techniques.

Adult↗
PubMed1990

[Friction sound as an objective sign of completion of root planing].

Root planing is one of the most important procedures in periodontal treatment. However, there are no objective clinical signs to indicate completion of this procedure. The purpose of this study was to examine the friction sound produced by curettes and root surfaces during root planing and to test the possibility of utilizing the sound changes as an objective parameter for evaluating completion of the procedure. The study consisted of a clinical and laboratory experiment. Seven periodontally diseased teeth were utilized in the clinical trial. During scaling and root planing with the Gracey curette, the friction sound was clinically analyzed with a sound spectrograph. The root surface, in situ, was observed by scanning electron microscopy (SEM) with the replica technique. Twenty-one periodontally diseased teeth were used in the laboratory study. Root planed surfaces were classified as pre-root planed and post-root planed according to their friction sounds during root planing. Each surface was examined by the following methods: 1) measuring root surface roughness 2) SEM observations 3) determination of number of adherent cells by the cultured fibroblast technique. As a result, post-root planed surfaces were well root planed as evaluated by SEM observations and the profilometer. Similarly, adherent cell counts were increased on post-root planed surfaces. These results indicated the possible usefulness of friction sound analysis to judge the completion of root planing.

Cell Adhesion↗
PubMed2005

Association between phonocardiographic third and fourth heart sounds and objective measures of left ventricular function.

CONTEXT: The third (S3) and fourth (S4) heart sounds detected by phonocardiography are considered to represent the criterion standards of the gallop sounds, but their test characteristics have not been explored. OBJECTIVE: To determine the diagnostic test characteristics of the S3 and S4 for prediction of left ventricular dysfunction using a computerized heart sound detection algorithm. DESIGN, SETTING, AND PARTICIPANTS: Prospective study of 90 adult patients undergoing elective left-sided heart catheterization at a single US teaching hospital between August 2003 and June 2004. The mean age was 62 (SD, 13) years (range, 24-90 years) and 61 (68%) were male. Within a 4-hour period, participants underwent computerized heart sound phonocardiographic analysis, cardiac catheterization, transthoracic echocardiography, and blood sampling for assessment of an S3/S4, left ventricular end-diastolic pressure (LVEDP), left ventricular ejection fraction (LVEF), and B-type natriuretic peptide (BNP), respectively. MAIN OUTCOME MEASURES: Diagnostic test characteristics of the computerized phonocardiographic S3 and S4 using markers of left ventricular function as criterion standards. RESULTS: Mean (SD) LVEDP was significantly elevated (18.4 [6.9] mm Hg vs 12.1 [7.3] mm Hg; P<.001), mean (SD) LVEF was reduced (49.4% [20.2%] vs 63.6% [14.8%]; P<.001), and median (interquartile range) BNP was elevated (330 [98-1155] pg/mL vs 86 [41-192] pg/mL; P<.001) in those with an S3, S4, or both compared with patients without a diastolic heart sound. The sensitivities of these heart sounds to detect an elevated LVEDP, reduced LVEF, or elevated BNP were 41%, 52%, and 32% for an S3, and 46%, 43%, and 40% for an S4, respectively. For abnormal levels of the same markers of ventricular function, the specificities of the S3 were 92%, 87%, and 92%, while the specificities of the S4 were 80%, 72%, and 78%, respectively. CONCLUSIONS: Neither the phonocardiographic S3 nor the S4 is a sensitive marker of left ventricular dysfunction. The phonocardiographic S3 is specific for left ventricular dysfunction and appears to be superior to the moderate specificity of the phonocardiographic S4.

Adult↗
PubMed2005

Human brain activation during passive listening to sounds from different locations: an fMRI and MEG study.

Recent animal and human studies indicate the existence of a neural pathway for sound localization, which is similar to the "where" pathway of the visual system and distinct from the sound identification pathway. This study sought to highlight this pathway using a passive listening protocol. We employed fMRI to study cortical areas, activated during the processing of sounds coming from different locations, and MEG to disclose the temporal dynamics of these areas. In addition, the hypothesis of different activation levels in the right and in the left hemispheres, due to hemispheric specialization of the human brain, was investigated. The fMRI results indicate that the processing of sound, coming from different locations, activates a complex neuronal circuit, similar to the sound localization system described in monkeys known as the auditory "where" pathway. This system includes Heschl's gyrus, the superior temporal gyrus, the supramarginal gyrus, and the inferior and middle frontal lobe. The MEG analysis allowed assessment of the timing of this circuit: the activation of Heschl's gyrus was observed 139 ms after the auditory stimulus, the peak latency of the source located in the superior temporal gyrus was at 156 ms, and the inferior parietal lobule and the supramarginal gyrus peaked at 162 ms. Both hemispheres were found to be involved in the processing of sounds coming from different locations, but a stronger activation was observed in the right hemisphere.

Acoustic Stimulation↗
PubMed1997

Effects of tectal grafts on sound localization deficits induced by inferior colliculus lesions in hooded rats.

The goals of this research were to examine the role of the inferior colliculus (IC) in mediating sound localization behavior and the ability of tectal grafts to restore function after IC ablation in the Long-Evans rat. Previous work has suggested that the IC is a major center for processing of information used in localizing sound sources in space. Adult rats were trained on a lick suppression paradigm to discriminate the location of the second pulse in a noise burst pair presented in the horizontal interaural plane. Following baseline testing, rats received bilateral IC lesions, bilateral lesions followed in 1 week by bilateral tectal grafts, or were sham operated. Sound localization ability was then tested 15 to 30 days and 40 to 50 days following surgical procedures. Performance across experimental groups was statistically the same during baseline testing. During the first operative test period lesion-only and grafted animals showed deficits in sound localization ability relative to controls. By the second postoperative test period control and grafted animals did not differ statistically in sound localization ability and performance of both groups was superior to that of lesion-only animals. Histology revealed a similar extent of IC damage in lesion-only and lesion-graft animals and revealed the presence of implanted tectal tissue in all grafted animals. There was significant neuron loss in the dorsal nucleus of lateral lemniscus (DNLL) in lesion-only animals relative to grafted rats and sham controls. Behavioral results suggest that the IC of pigmented rat is important for sound localization ability. The sparing of DNLL neurons in grafted animals suggests that the tectal grafts may directly integrate into or aid intrinsic recovery of the host auditory pathway.

Animals↗
PubMed2000

Discrimination of speech and of complex nonspeech sounds of different temporal structure in the left and right cerebral hemispheres.

The key question in understanding the nature of speech perception is whether the human brain has unique speech-specific mechanisms or treats all sounds equally. We assessed possible differences between the processing of speech and complex nonspeech sounds in the two cerebral hemispheres by measuring the magnetic equivalent of the mismatch negativity, the brain's automatic change-detection response, which was elicited by speech sounds and by similarly complex nonspeech sounds with either fast or slow acoustic transitions. Our results suggest that the right hemisphere is predominant in the perception of slow acoustic transitions, whereas neither hemisphere clearly dominates the discrimination of nonspeech sounds with fast acoustic transitions. In contrast, the perception of speech stimuli with similarly rapid acoustic transitions was dominated by the left hemisphere, which may be explained by the presence of acoustic templates (long-term memory traces) for speech sounds formed in this hemisphere.

Adolescent↗
PubMed2001

Distinct pathways involved in sound recognition and localization: a human fMRI study.

Evidence from psychophysical studies in normal and brain-damaged subjects suggests that auditory information relevant to recognition and localization are processed by distinct neuronal populations. We report here on anatomical segregation of these populations. Brain activation associated with performance in sound identification and localization was investigated in 18 normal subjects using fMRI. Three conditions were used: (i) comparison of spatial stimuli simulated with interaural time differences; (ii) identification of environmental sounds; and (iii) rest. Conditions (i) and (ii) required acknowledgment of predefined targets by pressing a button. After coregistering, images were normalized and smoothed. Activation patterns were analyzed using SPM99 for individual subjects and for the whole group. Sound recognition and localization activated, as compared to rest, inferior colliculus, medial geniculate body, Heschl gyrus, and parts of the temporal, parietal, and frontal convexity bilaterally. The activation pattern on the fronto-temporo-parietal convexity differed in the two conditions. Middle temporal gyrus and precuneus bilaterally and the posterior part of left inferior frontal gyrus were more activated by recognition than by localization. Lower part of inferior parietal lobule and posterior parts of middle and inferior frontal gyri were more activated, bilaterally, by localization than by recognition. Regions selectively activated by sound recognition, but not those selectively activated by localization, were significantly larger in women. Passive listening paradigm revealed segregated pathways on superior temporal gyrus and inferior parietal lobule. Thus, anatomically distinct networks are involved in sound recognition and sound localization.

Adult↗
PubMed1996

Effects of sound direction on the processing of amplitude-modulated signals in the frog inferior colliculus.

Single-unit recordings were made from 143 neurons in the frog (Rana p. pipiens) inferior colliculus (IC) to investigate how free-field sound direction influenced neural responses to sinusoidal-amplitude-modulated (SAM) tone and/or noise. Modulation transfer functions (MTFs) were derived from 3 to 5 sound directions within 180 degrees of frontal field. Five classes of MTF were observed: low-pass, high-pass, band-pass, multi-pass, and all-pass. For 64% of IC neurons, the MTF class remained unchanged when sound direction was shifted from contralateral 90 degrees to ipsilateral 90 degrees. However, the MTFs of more than half of these neurons exhibited narrower bandwidths when the loudspeaker was shifted to ipsilateral azimuths. There was a decrease in the cut-off frequency for neurons possessing low-pass MTFs, an increase in cut-off frequency for neurons showing high-pass MTFs, or a reduction in the pass-band for neurons displaying bandpass MTFs. These results suggest that sound direction can influence amplitude modulation (AM) frequency tuning of single IC neurons. Since changes in periodicity of SAM tones alter both the temporal parameters of sounds as well as the sound spectrum, we examined whether directional effects on spectral selectivity play a role in shaping the observed direction-dependent AM selectivity. The directional influence on AM selectivity to both SAM tone and SAM noise was measured in 62 neurons in an attempt to gain some insight into the mechanisms that underlie directionally-induced changes in AM selectivity. Direction-dependent changes in the shapes of the tone and noise derived MTFs were different for the majority of IC neurons (55/62) tested. These data indicate that a spectrally-based and a temporally-based mechanism may be responsible for the observed results.

Acoustic Stimulation↗
PubMed1993

Sound and vibration sensitivity of VIIIth nerve fibers in the frogs Leptodactylus albilabris and Rana pipiens pipiens.

1. Responses of 73 fibers to dorso-ventral vibration were recorded in the saccular and utricular branchlets of Rana pipiens pipiens using a ventral approach. The saccular branchlet contained nearly exclusively vibration-sensitive fibers (33 out of 36) with best frequencies (BFs) between 10 and 70 Hz, whereas none of the 37 fibers encountered in the utricular branchlet responded to dorso-ventral vibrations. 2. Using a dorsal approach we recorded from the VIIIth nerve near its entry in the brainstem and analyzed responses to both sound and vibration stimuli for 65 fibers in R. pipiens pipiens and 25 fibers in Leptodactylus albilabris. The fibers were classified as amphibian papilla (AP), basilar papilla (BP), saccular or vestibular fibers based on their location in the nerve. Only AP and saccular fibers responded to vibrations. The AP-fibers responded to vibrations from 0.01 cm/s2 and to sound from 40 dB SPL by increasing their spike rate. Best frequencies (BFs) ranged from 60 to 900 Hz, and only fibers with BFs below 500 Hz responded to vibrations. The fibers had identical BF's for sound and vibration. The saccular fibers had BFs ranging from 10 to 80 Hz with 22 fibers having BFs at 40-50 Hz. The fibers responded to sound from 70 dB SPL and to vibrations from 0.01 cm/s2. 3. No differences in sensitivity, tuning or phase-locking were found between the two species, except that most BP-fibers in R. pipiens pipiens had BFs from 1.2 to 1.4 kHz, whereas those in L. albilabris had BFs from 2.0 to 2.2 kHz (matching the energy peak of L. albilabris' mating call). 4. The finding that the low-frequency amphibian papilla fibers are extremely sensitive to vibrations raises questions regarding their function in the behaving animal. They may be substrate vibration receptors, respond to sound-induced vibrations or bone-conducted sound.

Animals↗