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PubMed2002

The rattling sound of rattlesnakes (Crotalus viridis) as a communicative resource for ground squirrels (Spermophilus beecheyi) and burrowing owls (Athene cunicularia).

Animal communication involves very dynamic processes that can generate new uses and functions for established communicative activities. In this article, the authors describe how an aposematic signal, the rattling sound of rattlesnakes (Crotalus viridis), has been exploited by 2 ecological associates of rattlesnakes: (a) California ground squirrels (Spermophilus beecheyi) use incidental acoustic cues in rattling sounds to assess the danger posed by the rattling snake, and (b) burrowing owls (Athene cunicularia) defend themselves against mammalian predators by mimicking the sound of rattling. The remarkable similarity between the burrowing owl's defensive hiss and the rattlesnake's rattling reflects both exaptation and adaptation. Such exploitation of the rattling sound has favored alternations in both the structure and the deployment of rattling by rattlesnakes.

Animal Communication↗
PubMed1980

Development of directional responses to sounds in the rat (Rattus norvegicus).

The first of two experiments was carried out to examine the tendency of rat infants (13-20 days of age) to approach auditory stimulation. Tests were conducted in a circular maze with a central start area and eight response areas at the periphery. Stimuli were played back over a loudspeaker placed behind one of the eight response areas. Signals included species calls at high and low intensities. A control condition with blank tapes was also used. The subjects showed a clear tendency to approach the low-intensity playback of a species "social" vocalization but did not approach the other stimuli. The aim of the second experiment was to investigate the importance of binaural cues for localization. Rat infants were tested with one ear blocked, both ears blocked, or neither ear blocked. The effect of the ear plug(s) was to attenuate the sound approximately 10 dB. The results indicated that only the binaurally blocked and normal control subjects approached the sound source at above chance levels. The failure of subjects in the monaural group to approach the sound probably resulted from a disruption of binaural cues. The ability of rat infants to localize sounds and process binaural cues is discussed in relation to the onset of hearing and in terms of physiological response that are present early in ontogeny.

Aging↗
PubMed1998

Relearning sound localization with new ears.

Because the inner ear is not organized spatially, sound localization relies on the neural processing of implicit acoustic cues. To determine a sound's position, the brain must learn and calibrate these cues, using accurate spatial feedback from other sensorimotor systems. Experimental evidence for such a system has been demonstrated in barn owls, but not in humans. Here, we demonstrate the existence of ongoing spatial calibration in the adult human auditory system. The spectral elevation cues of human subjects were disrupted by modifying their outer ears (pinnae) with molds. Although localization of sound elevation was dramatically degraded immediately after the modification, accurate performance was steadily reacquired. Interestingly, learning the new spectral cues did not interfere with the neural representation of the original cues, as subjects could localize sounds with both normal and modified pinnae.

Adaptation, Physiological↗
PubMed1995

A common neural code for frequency- and amplitude-modulated sounds.

Most naturally occurring sounds are modulated in amplitude or frequency; important examples include animal vocalizations and species-specific communication signals in mammals, insects, reptiles, birds and amphibians. Deciphering the information from amplitude-modulated (AM) sounds is a well-understood process, requiring a phase locking of primary auditory afferents to the modulation envelopes. The mechanism for decoding frequency modulation (FM) is not as clear because the FM envelope is flat (Fig. 1). One biological solution is to monitor amplitude fluctuations in frequency-tuned cochlear filters as the instantaneous frequency of the FM sweeps through the passband of these filters. This view postulates an FM-to-AM transduction whereby a change in frequency is transmitted as a change in amplitude. This is an appealing idea because, if such transduction occurs early in the auditory pathway, it provides a neurally economical solution to how the auditory system encodes these important sounds. Here we illustrate that an FM and AM sound must be transformed into a common neural code in the brain stem. Observers can accurately determine if the phase of an FM presented to one ear is leading or lagging, by only a fraction of a millisecond, the phase of an AM presented to the other ear. A single intracranial image is perceived, the spatial position of which is a function of this phase difference.

Brain Stem↗
PubMed1996

Enhancement of selective listening by illusory mislocation of speech sounds due to lip-reading.

Mechanisms of human attention allow selective processing of just the relevant events among the many stimuli bombarding our senses. Most laboratory studies examine attention within just a single sense, but in the real world many important events are specified multimodally, as in verbal communication. Speech comprises visual lip movements as well as sounds, and lip-reading contributes to speech perception, even for listeners with good hearing, by a process of audiovisual integration. Such examples raise the problem of how we coordinate our spatial attention across the sensory modalities, to select sights and sounds from a common source for further processing. Here we show that this problem is alleviated by allowing some cross-modal matching before attentional selection is completed. Cross-modal matching can lead to an illusion, whereby sounds are mislocated at their apparent visual source; this crossmodal illusion can enhance selective spatial attention to speech sounds.

Attention↗
PubMed2003

Plasticity in human sound localization induced by compressed spatial vision.

Auditory and visual target locations are encoded differently in the brain, but must be co-calibrated to maintain cross-sensory concordance. Mechanisms that adjust spatial calibration across modalities have been described (for example, prism adaptation in owls), though rudimentarily in humans. We quantified the adaptation of human sound localization in response to spatially compressed vision (0.5x lenses for 2-3 days). This induced a corresponding compression of auditory localization that was most pronounced for azimuth (minimal for elevation) and was restricted to the visual field of the lenses. Sound localization was also affected outside the field of visual-auditory interaction (shifted centrally, not compressed). These results suggest that spatially modified vision induces adaptive changes in adult human sound localization, including novel mechanisms that account for spatial compression. Findings are consistent with a model in which the central processing of sound location is encoded by recruitment rather than by a place code.

Acoustic Stimulation↗
PubMed2000

Measuring sound in hospital nurseries.

This article provides practical advice on how to document sound levels in a nursery: How do you use sound-level meters, noise dosimeters, and spectrum analyzers? Where is the best position for microphones in a sound survey? How do you present results to nursery staff? The goal is to provide informal instruction on how to use these devices and interpret their measurements. The intended audience is medical personnel, not engineers. A companion article in this issue provides background on the technical aspects of sound measurement. There is an appendix with hints about finding help and purchasing equipment.

Acoustics↗
PubMed2000

Hearing and behavioral responses to sound in full-term newborns.

This article, addressed to clinicians caring for and interacting with newborns, summarizes information from the research literature about newborn infants' hearing and behavioral responses to sound. While the emphasis is on current knowledge, older studies show how the investigators' assumptions have influenced the questions they have asked. Although these studies do not make up a neat package of information for clinicians, they do reveal broad outlines of newborn hearing abilities and the affects of sound on sleeping, quieting from crying, habituating, and paying attention. The newborn's responses to and preferences for particular sounds such as speech, music, and heartbeats are reviewed. These studies present the term newborn as an active listener and learner who, despite a somewhat immature auditory system and a limited repertoire of behavioral responses, is highly discriminating regarding the sounds of speech and whose efforts at sleeping, quieting, and paying attention may be hindered by noise such as that commonly found in hospital nurseries.

Habituation, Psychophysiologic↗
PubMed2000

Physiological effects of sound on the newborn.

Excessive sound is an acknowledged problem in neonatal intensive care units (NICUs); however, there is relatively little objective information about the effects of sound on the newborn. The cardiovascular and respiratory systems have been the most extensively studied systems. The patterns of response in these systems may be influenced by a variety of factors, including: the intensity of the sound, the infant's behavioral state, the infant's maturity and postnatal age, and the perinatal history. This article reviews the known cardiovascular, respiratory, and other physiological effects of sound on neonates.

Cardiovascular Physiological Phenomena↗
PubMed1977

Sound pressure in insert earphone couplers and real ears.

It is known that sound pressure, measured in couplers via a probe-tube microphone, often shows a pressure vs frequency response that drops sharply at a single frequency. In this study sound pressure was theoretically determined at various locations within a hard-walled cylindrical cavity, driven by a constant-volume velocity source with circular symmetry. At each location in the volume, a transfer impedance was defined as the ratio of pressure to inlet-volume velocity. In the region around the inlet, the transfer impedance passes through zero as it changes from negative to positive reactance with increasing frequency. Two hard-walled cavity examples were examined in detail (1) the main cavity of a 2-cm3 HA-2 coupler, and (2) a cavity having dimensions approximately equal to the occluded ear canal between an ear-mold tip and the eardrum. Contours of constant minimum sound pressure vs frequency are given for these two cylindrical volumes with experimental verification. Implications for probe microphone calibration and measurement of sound pressure in ears are discussed.

Acoustic Impedance Tests↗
PubMed1996

Canine tooth guidance and temporomandibular joint sounds in non-patients and patients.

In 46 non-patients and 46 patients, the authors examined the presence (+) and absence (-) of canine tooth guidance (CG), i.e. dynamic dental articulation events in contrast to static dental occlusion events. During a right and a left laterotrusion of the mandible, the number of simple, mutually exclusive and exhaustive tooth guidance events (possibilities) was four. In addition, the authors examined the associations between temporomandibular joint (TMJ) sounds and canine guidance events. In non-patients, CG+ was relatively infrequent (30%), and CG- was relatively frequent (70%). In patients, CG+ was relatively infrequent (22%), and CG- was relatively frequent (78%). In both non-patients and patients, bilateral CG+ was rather infrequent (15%). In both non-patients and patients with the presence of TMJ sounds, CG+ was relatively infrequent (38%) while CG- was relatively frequent (61%). In non-patients as well as patients, no evidence was found that distal CG+ (putative lateral retrusive guidance) was associated with ipsilateral TMJ sounds (relative risk = 0%), nor that the association between mesial CG+ (putative lateral protrusive guidance) and ipsilateral TMJ sounds was beyond that of mere chance (relative risk = 50%).

Cuspid↗
PubMed1996

Mediotrusive tooth guidance and temporomandibular joint sounds in non-patients and patients.

In 46 non-patients and 46 patients, the authors examined the presence (+) and the absence (-) of laterotrusive (LG) and mediotrusive (MG) tooth guidance, i.e. dynamic dental articulation events in contrast to static dental occlusion events. During a right and left laterotrusion/mediotrusion of the mandible, the number of compound, mutually exclusive and exhaustive tooth guidance events (possibilities) was six. In addition, the presence and the absence of temporomandibular joint (TMJ) sounds, provoked TMJ pains, and the associations between TMJ sounds and tooth guidance events were examined. In non-patients, LG+ and MG+ was relatively infrequent (30%) while LG+ and MG- was relatively frequent (70%). In patients, LG+ and MG+ was relatively frequent (58%) while LG+ and MG- was relatively infrequent (42%). LG- and MG+ was absent in non-patients and rare in patients (3%). Either unilateral or bilateral MG+ was relatively infrequent in non-patients (30%) and relatively frequent in patients (59%). Bilateral MG+ was relatively infrequent in non-patients (20%) and relatively frequent in patients (52%). Either unilateral or bilateral TMJ sounds were relatively infrequent in non-patients (39%) and relatively frequent in patients (74%). Either unilateral or bilateral provoked TMJ pains were absent in non-patients and relatively frequent in patients (72%). The authors found no evidence that TMJ sounds were associated with the ipsilateral absence of so-called balancing contacts (MG-) in non-patients and patients. Finally, no evidence supporting the use of a so-called positive predictive value, and "extension concept' of probability theory was found.

Adult↗
PubMed1998

Subjective assessment of temporomandibular joint sounds.

If it could be shown that the human ear was sufficiently sensitive to describe TMJ sounds, there would be no need to use sophisticated electronic equipment to analyse the sounds. To test this, the ability of normal listeners to distinguish the subtle changes in position, pitch, duration and latency present in TMJ sounds is measured using triangle tests to determine the just-noticeable differences. The results suggest that the human ear is a rather poor instrument for describing subtle differences in the position, duration and latency of TMJ sounds, but is capable of detecting small differences in frequency. It is therefore doubtful that the human ear can distinguish the reciprocal click associated with disc displacement with reduction from clicks due to defects of form on the basis of their relative position in the envelope of movement.

Computers↗
PubMed1999

False localization of TMJ sounds to side is an important source of error in TMD diagnosis.

The results of the study indicate that the head tissues act as a band pass filter that is far from flat. Instead there seems to be strong frequency variations in attenuation of transmitted sounds. The sounds are subject to phase shift and time delay, which can be used to decide from which TMJ the sound comes. Bilateral electronic recording with high sampling rate (>> 44 kHz) is needed to accurately and consistently identify the origin of a TMJ sound. Further studies on autopsy specimens and large subject groups are motivated.

Acoustics↗
PubMed2002

Opposing effects of head position on sound localization in blind and sighted human subjects.

Up to now, there is an unsolved contradiction between the view that the development of an auditory spatial representation needs calibration by vision and the psychophysical demonstration of quite precise sound localization in early blind humans. The present study provides a link between these two competing conceptions. Two experiments were conducted with congenitally or early blind subjects and sighted controls. In the first experiment, subjects pointed with their head to actual sound sources located in the azimuthal plane. In the second experiment, lateralization of dichotic sound stimuli, presented via headphones, was investigated with variation of head-to-trunk position. The results showed opposing systematic errors of sound localization or lateralization, depending on head position, made by blind and sighted subjects. These differences suggest that audiomotor feedback replaces vision so as to calibrate auditory space in blind individuals. That is, in contrast to the widespread opinion of compensation of visual loss by a general sharpening of audition, compensatory plasticity in the blind may specifically be related to enhanced processing of proprioceptive and vestibular information with the auditory spatial input.

Adaptation, Physiological↗
PubMed2002

Human cortical representation of virtual auditory space: differences between sound azimuth and elevation.

Sounds convolved with individual head-related transfer functions and presented through headphones can give very natural percepts of the three-dimensional auditory space. We recorded whole-scalp neuromagnetic responses to such stimuli to compare reactivity of the human auditory cortex to sound azimuth and elevation. The results suggest that the human auditory cortex analyses sound azimuth, based on both binaural and monaural localization cues, mainly in the hemisphere contralateral to the sound, whereas elevation in the anterior space and in the lateral auditory space in general, both strongly relying on monaural spectral cues, are analyzed in more detail in the right auditory cortex. The binaural interaural time and interaural intensity difference cues were processed in the auditory cortex around 100-150 ms and the monaural spectral cues later around 200-250 ms.

Acoustic Stimulation↗
PubMed2001

Prognostic importance of elevated jugular venous pressure and a third heart sound in patients with heart failure.

BACKGROUND: The independent prognostic value of elevated jugular venous pressure or a third heart sound in patients with heart failure is not well established. METHODS: We performed a retrospective analysis of the Studies of Left Ventricular Dysfunction treatment trial, in which 2569 patients with symptomatic heart failure or a history of it were randomly assigned to receive enalapril or placebo. The mean (+/-SD) follow-up was 32+/-15 months. The presence of elevated jugular venous pressure or a third heart sound was ascertained by physical examination on entry into the trial. The risks of hospitalization for heart failure and progression of heart failure as defined by death from pump failure and the composite end point of death or hospitalization for heart failure were compared in patients with these findings on physical examination and patients without these findings. RESULTS: Data on 2479 patients were complete and analyzed. In multivariate analyses that were adjusted for other markers of the severity of heart failure, elevated jugular venous pressure was associated with an increased risk of hospitalization for heart failure (relative risk, 1.32; 95 percent confidence interval, 1.08 to 1.62; P<0.01), death or hospitalization for heart failure (relative risk, 1.30; 95 percent confidence interval, 1.11 to 1.53; P<0.005), and death from pump failure (relative risk, 1.37; 95 percent confidence interval, 1.07 to 1.75; P<0.05). The presence of a third heart sound was associated with similarly increased risks of these outcomes. CONCLUSIONS: In patients with heart failure, elevated jugular venous pressure and a third heart sound are each independently associated with adverse outcomes, including progression of heart failure. Clinical assessment for these findings is currently feasible and clinically meaningful.

Aged↗
PubMed2001

Identification of visual stimuli is improved by accompanying auditory stimuli: the role of eye movements and sound location.

Can auditory signals influence the processing of visual information? The present study examined the effects of simple auditory signals (clicks and noise bursts) whose onset was simultaneous with that of the visual target, but which provided no information about the target. It was found that such a signal enhances performance in the visual task: the accessory sound reduced response times for target identification with no cost to accuracy. The spatial location of the sound (whether central to the display or at the target location) did not modify this facilitation. Furthermore, the same pattern of facilitation was evident whether the observer fixated centrally or moved their eyes to the target. The results were not altered by changes in the contrast (and therefore visibility) of the visual stimulus or by the perceived utility of the spatial location of the sound. We speculate that the auditory signal may promote attentional 'disengagement' and that, as a result, observers are able to process the visual target sooner when sound accompanies the display relative to when visual information is presented alone.

Adolescent↗