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PubMed1980

The precedence effect and its possible role in the avoidance of interaural ambiguities.

The precedence effect, the observation that sound-source localization is determined largely by the interaural cues associated with the earlier-arriving direct sound to the neglect of later-arriving reflections, was investigated in several psychophysical experiments. The first experiment employed a stimulus composed of a continuous noise and its delayed repetition to simulate a direct sound and a single reflection. Comparison of the interaural amplitude and phase differences in this stimulus with its judged lateral position showed that the interaural amplitude and phase differences in this stimulus with its judged lateral position showed that the interaural differences do not predict lateralization judgments as simply as does a knowledge of the temporal pattern of stimulation, given the precedence effect. Most of the experiments were attempts to outline the time course of the precedence effect by measuring just-noticeable differences in interaural time and intensity of brief (less than 5 ms) wide-band noise bursts. The principal finding of these experiments was that interaural sensitivity to changes in both time and intensity follows a nonmonotonic course after the abrupt onset of as ound. Sensitivity is degraded for a period from approximately 0.5 to 10 ms after onset, with the largest jnd's at delays of 2-3 ms. The precedence effect can be understood as resulting from this temporary lapse of interaural sensitivity. It was speculated that this temporal variation in interaural acuity serves to inhibit: (1) the representation of multiple and ambiguous interaural time delays between corresponding points on the waves of periodic stimuli; and (2) the extraction of interaural phase at frequencies greater than approximately 1400 Hz.

Acoustic Stimulation↗
PubMed2003

Unilateral hemispheric lesions disrupt parallel processing within the contralateral intact hemisphere: an auditory fMRI study.

Evidence from activation studies suggests that sound recognition and localization are processed in two distinct cortical networks that are each present in both hemispheres. Sound recognition and/or localization may, however, be disrupted by purely unilateral damage, suggesting that processing within one hemisphere may not be sufficient or may be disturbed by the contralateral lesion. Sound recognition and localization were investigated psychophysically and using fMRI in patients with unilateral right hemisphere lesions. Two patients had a combined deficit in sound recognition and sound localization, two a selective deficit in sound localization, one a selective deficit in sound recognition, and two normal performance in both tasks. The overall level of activation in the intact left hemisphere of the patients was smaller than in normal control subjects, irrespective of whether the patient's performance in the psychophysical tasks was impaired. Despite this overall decrease in activation strength, patients with normal performance still exhibited activation patterns similar to those of the control subjects in the recognition and localization tasks, indicating that the specialized brain networks subserving sound recognition and sound localization in normal subjects were also activated in the patients with normal performance, albeit to an altogether lesser degree. In patients with deficient performance, on the other hand, the activation patterns during the sound recognition and localization tasks were severely reduced, comprising fewer and partly atypical activation foci compared to the normal subjects. This indicates that impaired psychophysical performance correlates with a breakdown of parallel processing within specialized networks in the contralesional hemisphere.

Adult↗
PubMedDate not supplied

3-D-orientation with the octavolateralis system.

Fish detect and localize a sound source with inner ear receptors and with the mechanosensory lateral line. The inner ear of fish is sensitive to the water displacements caused by sound waves through a direct, inertial response by hair cell epithelia of the ear. Hearing specialists, such as goldfish and herring, have accessory peripheral structures that provide additional sensitivity to the pressure component of a sound wave. While the inner ear of fish responds to the whole body motions caused by sound waves and--in case of hearing specialists--to sound pressure, the lateral line is only sensitive to water motions relative to the surface of the fish and to local pressure gradients. Using lateral line and/or acoustic input, some fish can determine the direction and the distance to a sound source. Most likely they do so by exploiting some of the mechanisms described in this paper. Piscivorous fish may use lateral line input to detect the wakes caused by swimming fish. Even in the absence of light catfish, for instance, can follow a 10 s old, three-dimensional wake left by a prey fish over distances up to 55 prey-body length.

Acoustic Stimulation↗
PubMed2006

Ventriloquism aftereffects occur in the rear hemisphere.

After exposure to a consistent spatial disparity of auditory and visual stimuli, subjective localization of sound sources is usually shifted in the direction of the visual stimuli. This study investigates whether such aftereffects can be observed in humans after exposure to a conflicting bimodal stimulation in virtual reality and whether these aftereffects are confined to the trained locations. Fourteen subjects participated in an adaptation experiment, in which auditory stimuli were convolved with non-individual head-related transfer functions, delivered via headphones. First, we assessed the auditory localization of subjects in darkness. They indicated the perceived direction of a sound using an angular pointer. We then immersed the subjects in a virtual environment by means of a head-mounted display. They were asked to reproduce sequences of movements of virtual objects with a mouse click on the objects. However, we introduced a spatial disparity of 15 degrees between the visual event and the concurrent auditory stimulation. After 20 min of exposure, we tested the subjects again in total darkness to determine whether their auditory localization system had been modified by the conflicting visual signals. We observed a shift of subjective localization towards the left in both dorsal and frontal hemifields of the subject, mainly for auditory stimuli located in the right hemispace. This result suggests that interaural difference cues and monaural spectral cues were not equally adapted, and that visual stimuli mainly influence the processing of binaural directional cues of sound localization.

Acoustic Stimulation↗
PubMed2006

Cochlear efferent feedback balances interaural sensitivity.

Neurons in the lateral superior olive (LSO) compute sound location based on differences in interaural intensity, coded in ascending signals from the two cochleas. Unilateral destruction of the neuronal feedback from the LSO to the cochlea, the lateral olivocochlear efferents, disrupted the normal interaural correlation in response amplitudes to sounds of equal intensity. Thus, lateral olivocochlear feedback maintains the binaural balance in neural excitability required for accurate localization of sounds in space.

Acoustic Stimulation↗
PubMed1993

Direction-dependent spectral sensitivity and interaural spectral difference in a dolphin: evoked potential study.

Sensitivity and interaural intensity difference (IID) dependence on sound frequency and direction was measured in an Amazon river dolphin Inia geoffrensis by recording the auditory nerve evoked response from the body surface. The maximal sensitivity in the horizontal plane was found when the sound direction was 5 degrees to 10 degrees ipsilateral to the recorded ear; the direction dependence of sensitivity was more pronounced at higher frequencies than at lower ones. The IID reached its peak at small azimuthal angles (7.5 degrees to 15 degrees) and higher sound frequencies (100 kHz), or at large azimuthal angles (30 degrees to 45 degrees) and lower sound frequencies (20 to 30 kHz). Each sound direction featured its specific pattern of spectral sensitivity and of interaural spectral difference. The interaural spectral difference fluctuated within a range of more than 20 dB depending on sound direction. The data indicate that interaural intensity as well as spectral difference may be cues for binaural localization of sound direction by dolphins.

Acoustic Stimulation↗
PubMed1981

[Recognition of the emotional and prosodic characteristics of voice and complex nonverbal sounds by patients with local brain lesions].

Under examination there were 69 patients with cerebral cortex pathologies of various localization. Use was made of five speech tests and three non-speech ones that required identification or comparison of the sounds. it was found that all the patients had difficulties in discerning the emotional aspect of a speech communication, these difficulties being especially great in patients with disturbances of the speech, writing and reading. Maximal difficulties in fulfilling the requirements of the tests were revealed in patients with the temporal localization of the pathological foci. It is supposed that the emotional colouring of speech is discerned owing to a joint activity of a number of cortical zones in which the temporal divisions play the leading role.

Adult↗
PubMed1983

Central auditory processing. III. The "cocktail party" effect and anterior temporal lobectomy.

The capacity to selectively attend to only one of multiple, spatially separated. simultaneous sound sources--the "cocktail party" effect--was evaluated in normal subjects and in those with anterior temporal lobectomy using common environmental sounds. A significant deficit in this capacity was observed for those stimuli located on the side of space contralateral to the lobectomy, a finding consistent with the hypothesis that within each anterior temporal lobe is a mechanism that is normally capable of enhancing the perceptual salience of one acoustic stimulus on the opposite side of space, when other sound sources are present on that side. Damage to this mechanism also appears to be associated with a deficit of spatial localization for sounds contralateral to the lesion.

Attention↗
PubMed1993

Localization using nonindividualized head-related transfer functions.

A recent development in human-computer interfaces is the virtual acoustic display, a device that synthesizes three-dimensional, spatial auditory information over headphones using digital filters constructed from head-related transfer functions (HRTFs). The utility of such a display depends on the accuracy with which listeners can localize virtual sound sources. A previous study [F. L. Wightman and D. J. Kistler, J. Acoust. Soc. Am. 85, 868-878 (1989)] observed accurate localization by listeners for free-field sources and for virtual sources generated from the subjects' own HRTFs. In practice, measurement of the HRTFs of each potential user of a spatial auditory display may not be feasible. Thus, a critical research question is whether listeners can obtain adequate localization cues from stimuli based on nonindividualized transforms. Here, inexperienced listeners judged the apparent direction (azimuth and elevation) of wideband noisebursts presented in the free-field or over headphones; headphone stimuli were synthesized using HRTFs from a representative subject of Wightman and Kistler. When confusions were resolved, localization of virtual sources was quite accurate and comparable to the free-field sources for 12 of the 16 subjects. Of the remaining subjects, 2 showed poor elevation accuracy in both stimulus conditions, and 2 showed degraded elevation accuracy with virtual sources. Many of the listeners also showed high rates of front-back and up-down confusions that increased significantly for virtual sources compared to the free-field stimuli. These data suggest that while the interaural cues to horizontal location are robust, the spectral cues considered important for resolving location along a particular cone-of-confusion are distorted by a synthesis process that uses nonindividualized HRTFs.

Acoustic Stimulation↗
PubMed1987

Development of the auditory orientation response in the albino rat (Rattus norvegicus).

The development of head orientation to auditory stimulation was examined in rat pups at Postnatal Days 8, 11, 14, 17, and 20. The animals were tested in a quiet environment with single bursts of 65 dB (SPL) broad-band noise. A reflexive head turn toward the sound was first seen on Postnatal Day 14 and subsequently on Days 17 and 20. This result demonstrates that the onset of directional auditory responses occurred between Day 11 and Day 14. The role of binaural cues in early sound orientation was examined in 17-day-old pups with monaural ligation of the external meatus. These animals were unable to localize a sound source and consistently turned toward the side of the unligated ear regardless of the position of the stimulus. Thus binaural cues were shown to be important for head orientation to sound in early development. In a separate study, head orientation to high and low frequency tone pips was examined. Directional responses were first seen on Day 12 for a 16-kHz tone and Day 14 for a 2-kHz tone. These results indicate an earlier onset for orientation to high frequency sounds in the rat.

Aging↗
PubMed2000

Ultrasound-guided laparoscopic resection of pancreatic islet cell tumors.

Pancreatic islet cell tumors represent a diverse group of neuroendocrine lesions. These tumors may be singular or multiple, benign or malignant, sporadic, or part of the constellation of multiple endocrine neoplasia type 1. Tumors such as insulinomas and gastrinomas produce gastrointestinal peptides that lead to diagnosis. Nonfunctioning lesions may be found incidentally or by screening patients at high risk for such tumors. Successful management of patients with pancreatic islet cell tumors relies on accurate localization and sound operative technique. With proper preoperative localization, advanced laparoscopic methods can be used to manage patients with these pancreatic neoplasms. Preoperative localization of pancreatic islet cell tumors was difficult in the past. Standard imaging and localizing modalities, such as computed tomography scanning, magnetic resonance imaging, angiography, transabdominal sonography, and portal venous sampling, yield only 24% to 75% accuracy. Consequently, many biochemically suspected lesions cannot be imaged with current techniques. Decreased tactile sensation of laparoscopy adds complexity to intraoperative identification. Endoscopic sonography and laparoscopic sonography provide accurate preoperative and intraoperative localization to enhance laparoscopic and open resection. The authors treated two patients with islet cell neoplasms using endoscopic sonography to preoperatively visualize the tumors and laparoscopic sonography to guide laparoscopic enucleation. Their approach and difficulties are discussed.

Adenoma, Islet Cell↗
PubMed2004

Processing of frequency-modulated sounds in the lateral auditory belt cortex of the rhesus monkey.

Single neurons were recorded from the lateral belt areas, anterolateral (AL), mediolateral (ML), and caudolateral (CL), of nonprimary auditory cortex in 4 adult rhesus monkeys under gas anesthesia, while the neurons were stimulated with frequency-modulated (FM) sweeps. Responses to FM sweeps, measured as the firing rate of the neurons, were invariably greater than those to tone bursts. In our stimuli, frequency changed linearly from low to high frequencies (FM direction "up") or high to low frequencies ("down") at varying speeds (FM rates). Neurons were highly selective to the rate and direction of the FM sweep. Significant differences were found between the 3 lateral belt areas with regard to their FM rate preferences: whereas neurons in ML responded to the whole range of FM rates, AL neurons responded better to slower FM rates in the range of naturally occurring communication sounds. CL neurons generally responded best to fast FM rates at a speed of several hundred Hz/ms, which have the broadest frequency spectrum. These selectivities are consistent with a role of AL in the decoding of communication sounds and of CL in the localization of sounds, which works best with broader bandwidths. Together, the results support the hypothesis of parallel streams for the processing of different aspects of sounds, including auditory objects and auditory space.

Animals↗
PubMed2000

A low-cost approach to public health education using multimedia packages.

The effect of health education programmes depends on the number of people exposed to the messages, as well as the method and style in which the information is transmitted. We conducted a pilot project to encourage healthier lifestyles by presenting culturally sensitive information using a variety of media. Material intended to provoke discussion was shared with a range of audiences in Barbados and Montserrat in the West Indies by a series of lecture discussions, which were videorecorded for local television and sound recorded for local radio. The lecture was also disseminated by newspaper articles, a special magazine and by publication on the Internet. The aim of the project was to achieve maximum effect for minimum effort, thus making optimum use of resources. The feedback obtained at the lecture discussions and in response to the radio broadcasts and newspaper articles provided a needs assessment on which to base a definitive programme, and confirmed that radio and television are the most effective media for health education.

Barbados↗
PubMedDate not supplied

Masking level difference: another tool for the evaluation of peripheral and cortical defects.

Masking level difference (MLD) due to binaural unmasking was measured for speech signals (5-word meaningful sentences) masked by broad-band noise. Tests were carried out in a group of patients with unilateral cerebral lesions of vascular origin and apparently normal pure-tone audiograms (CNS patients), in a control group (normally hearing young adults) and in 5 other groups of patients (conductive symmetrical hearing loss, conductive asymmetrical hearing loss, bilateral presbyacusis, unilateral sudden deafness, Menière's disease). Testing pattern implied three or more S/N ratios in the listening conditions, of SmNm, Sdelta tNo and SmNu (noise correlated), and the speech signal intensity was 70 dB SPL re 20 muPa for the control group, whilst for the pathological cases, speech level intensities were established by means of alternate binaural loudness balance and simultaneous balancing median-plane localization procedures to assess subjective suprathreshold sound image localization at the midline. The results obtained in the control group and in the patients are discussed. With specific reference to the CNS patients, a statistically significant tendency was evident for the binaural condition to produce more MLD when the ear leading in time was ipsilateral to the normal hemisphere. The importance of this and of sensitized speech testing methods in CNS disorders is discussed on the basis of the results obtained in the CNS patients.

Acoustic Stimulation↗
PubMedDate not supplied

Anatomy of the auditory cortex.

Cortical auditory areas located in the superior temporal region (STR) in monkey and human. The primary auditory area (AI) occupies the cortex of the supratemporal plane (STP) and is surrounded by auditory association areas in circular sulcus and superior temporal gyrus (STG). Architectonic studies have parcellated auditory areas into a number of subregions. Beginning from the temporal polar proisocortex up to the parietal cortex, these areas shows progressive laminar differentiation, and are arranged into three parallel lines. The most medial line occupies the cortex of the circular sulcus. The regions of this line maintains limbic features and is termed as root line. Another line is located in STG. The regions of this line show progressive emphasis in the third and fourth layer neurons and is termed as belt line. Interposed between root and belt line is a core line located in STP. In this line there is greater accumulation of fourth layer neurons. Recent physiological studies have outlined several auditory representations surrounding AI. These auditory representations correspond to above mentioned architectonic subregions of STR. The subregions within each line have bidirectional connectional laminar specificity. The feedforward connections originate from the supragranular layer III and terminate in the around layer IV of the rostrally adjacent region. Feedback projections in contrast stem from the infragranular layers and terminate in layer I. The long association connections of auditory areas are with the prefrontal cortex (PFC), the multimodal areas and the limbic regions, and are derived from belt and root line areas of STR. These projections follow the rostro-caudal architectonic differentiation of STR. Thus the rostral STG areas are mainly connected with orbital and medial PFC areas whereas the caudal STG areas are connected with caudal PFC. The intermediate STG areas are preferentially related to the lateral PFC regions. It seems that STG-PFC connections are between the areas with similar level of architectonic differentiation. The thalamic connections of the subregions of STR also follow the architectonic organizations. The core line areas are preferentially related to ventral nucleus (MGv) of medial geniculate nucleus (MGN) whereas the root and belt line areas are connected respectively to magnocellular (MGmc) and dorsal (MGd) subdivisions of MGN. The root and belt areas share some connections and are also related to pulvinar, suprageniculate, dorsomedial and intralaminar nuclei. It seems therefore that progressive laminar and tripartrate organization of auditory regions of STR is reflected in intrinsic, association and thalamic connections. The feedforward connections may be engaged in analysis of external environmental cues whereas feedback connections may have a role in matching learned or stored information with incoming auditory signals. The preferential core line connectivity with MGv may be involved in spectral analysis of sound whereas the connections of the belt and root areas with MGmc, MGd, and pulvinar may have role in sound pattern recognition, auditory memory, the localization of sound in space as well as matching auditory information with other modalities.

Animals↗
PubMed2005

Benefit of wearing a hearing aid on the unimplanted ear in adult users of a cochlear implant.

The purpose of this investigation was to document performance of participants wearing a cochlear implant and hearing aid in opposite ears on speech-perception and localization tests. Twelve individuals who wore a cochlear implant and a hearing aid on contralateral ears were tested on their abilities to understand words in quiet and sentences in noise, and to localize everyday sounds. All speech stimuli were presented from the front, with the noise stimuli presented from the front, the right, or the left at a 90 degrees angle. Binaural summation in quiet and in noise, binaural squelch effects, and localization were studied to determine bilateral advantages. The magnitude of the monaural head shadow effect (the difference in unilateral performance when noise was facing the unilateral device vs. when the noise was opposite the unilateral device) also was studied. The test setup for localization was composed of an 8-speaker array spanning an arc of approximately 108 degrees in front of each participant. Group results yielded a statistically significant combined benefit of wearing a hearing aid in conjunction with a cochlear implant on opposite ears in noise conditions. Those participants who received a binaural advantage in 1 condition did not necessarily show a binaural advantage in another. Only 2 participants out of 12 were able to localize when wearing 2 devices. Further efforts are required to improve the integration of information from combined use of cochlear implant and hearing aid devices for enhancement of speech perception in noise and localization.

Aged↗
PubMed2004

Complex auditory behaviour emerges from simple reactive steering.

The recognition and localization of sound signals is fundamental to acoustic communication. Complex neural mechanisms are thought to underlie the processing of species-specific sound patterns even in animals with simple auditory pathways. In female crickets, which orient towards the male's calling song, current models propose pattern recognition mechanisms based on the temporal structure of the song. Furthermore, it is thought that localization is achieved by comparing the output of the left and right recognition networks, which then directs the female to the pattern that most closely resembles the species-specific song. Here we show, using a highly sensitive method for measuring the movements of female crickets, that when walking and flying each sound pulse of the communication signal releases a rapid steering response. Thus auditory orientation emerges from reactive motor responses to individual sound pulses. Although the reactive motor responses are not based on the song structure, a pattern recognition process may modulate the gain of the responses on a longer timescale. These findings are relevant to concepts of insect auditory behaviour and to the development of biologically inspired robots performing cricket-like auditory orientation.

Acoustic Stimulation↗
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↗