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PubMed2006

BAHA in children and adolescents with unilateral or bilateral conductive hearing loss: a study of outcome.

OBJECTIVES: Bilateral BAHAs in adults with bilateral hearing loss (BHL) have proven to be superior to unilateral fitting, in both audiologically measurements and in overall patient satisfaction. There have been no similar studies in children. Furthermore, a recent meta-analysis of children with unilateral hearing loss (UHL) has shown numerous negative consequences. The objectives of the study were to investigate whether fitting of bilateral BAHAs in children with conductive BHL give additional hearing benefits, to investigate the effects of unilateral hearing aids in children with conductive UHL, and to identify different aspects of auditory problems in children with conductive UHL or BHL. STUDY DESIGN: This was a prospective study involving 22 children with either conductive UHL (unaided or with unilateral hearing aid) or conductive BHL (with unilateral or bilateral BAHAs) and 15 controls. METHODS: Baseline audiometry, tone thresholds in a sound field, speech recognition in noise and sound localization were tested without, and with unilateral and bilateral hearing aids. Two questionnaires, MAIS & MUSS and IOI-HA, were completed. RESULTS: Two problem areas were identified in the children with hearing impairment: in reactions to sounds and in intelligibility of speech. An additional BAHA in the children with BHL resulted in a tendency to have improved hearing in terms of better sound localization and speech recognition in noise. Fitting of unilateral hearing aids in the children with UHL gave some supplementary benefit in terms of better speech recognition in noise but no positive effect on ability to localize sound could be detected. Even so, all children fitted with hearing aids - either unilaterally or bilaterally - reported a positive outcome with their devices in the self-assessment questionnaire. CONCLUSIONS: Children with either UHL or BHL displayed several problems within the hearing domain. Fitting of bilateral BAHAs in children with BHL and of a single-sided hearing aid in children with UHL appears to have some supplementary audiological benefits and also renders high patient satisfaction. In order to investigate the possible supplementary effects of hearing aids, a 3-month trial of BAHA on Softband, either unilaterally or bilaterally, may be of value in children with conductive UHL or BHL, respectively.

Adolescent↗

PubMed2001

Two types of auditory neglect.

Auditory neglect, defined as inattention to stimuli within the left hemispace, is mostly reported in association with left ear extinction in dichotic listening. However, it remains disputed as to how far dichotic extinction reflects a primary attentional deficit and is thus appropriate for the diagnosis of auditory neglect. We report here on four patients who presented left ear extinction in dichotic listening following right unilateral hemispheric lesions. Auditory spatial attention was assessed with two additional tasks: (i) diotic test by means of interaural time differences (ITDs), simulating bilateral simultaneous spatial presentation of the dichotic tasks without the inconvenience of interaural intensity or content difference; and (ii) sound localization. A hemispatial asymmetry on the ITD diotic test or a spatial bias on sound localization were found to be part of auditory neglect. Two patients (J.C.N. and M.B.) presented a marked hemispatial asymmetry favouring the ipsilesional hemispace in the ITD diotic test, but did not show any spatial bias in sound localization. Two other patients (A.J. and E.S.) had the reverse profile: no hemispatial asymmetry in the ITD diotic test, but a severe spatial bias directed to the ipsilesional side in sound localization. J.C.N. and M.B. had mainly subcortical lesions affecting the basal ganglia. A.J. and E.S. had cortical lesions in the prefrontal, superior temporal and inferior parietal areas. Thus, there are two behaviourally and anatomically distinct types of auditory neglect characterized by: (i) deficit in allocation of auditory spatial attention following lesions centred on basal ganglia; or (ii) distortion of auditory spatial representation following frontotemporoparietal lesions.

Adult↗

PubMed1989

Localization of sound in rooms. IV: The Franssen effect.

The Franssen effect is an illusion that causes human listeners to make large errors in localizing a sound source. This paper describes steps taken to convert the illusion into an experiment in order to study the localization precedence effect as it operates in rooms. The results of the experiment suggest that there are two components to the illusion: The first is the inability of listeners to localize a sine tone in a room in the absence of an onset; the second is the obscuring of modulation cues by the irregular transient response of a room. Experiments show that the Franssen effect fails completely in an anechoic environment, as expected if the effect depends upon the implausibility of steady-state cues in a room. The Franssen effect also fails when the spectrum of the sound is dense.

Auditory Perception↗

PubMed1987

Speculations about noise and the evolution of vertebrate hearing.

Two of the most conspicuous and celebrated properties of human hearing--the abilities to discriminate pitch and to localize sound sources, may have been secondary derivations to which the ear was preadapted by having evolved in the inevitable presence of noise.

Adaptation, Physiological↗

PubMed2004

Age-dependent changes in the lateral superior olive of the gerbil (Meriones unguiculatus).

Data from humans and animal models provide evidence for an age-dependent impairment in the ability to localize sound. The lateral superior olive (LSO) in the ascending auditory pathway is one important center involved in processing of binaural auditory stimuli. To identify potential age-dependent changes we characterized the LSO in young (< 15 months) and old (> or =3 years) gerbils with a special emphasis on the expression of GABA- and glycine-like immuno-reactivity. The dimensions of the LSO, as well as the number and density of glycine- and GABA-immuno-reactive neurons, were not significantly different between young and old gerbils. The size of glycine- and GABA-immuno-reactive neurons was significantly reduced in the high-frequency (medial) limb of the LSO. Over all, age-dependent changes in the LSO of the gerbil were small.

Aging↗

PubMed2003

Parallel auditory pathways: projection patterns of the different neuronal populations in the dorsal and ventral cochlear nuclei.

The cochlear nuclear complex gives rise to widespread projections to nuclei throughout the brainstem. The projections arise from separate, well-defined populations of cells. None of the cell populations in the cochlear nucleus projects to all brainstem targets, and none of the targets receives inputs from all cell types. The projections of nine distinguishable cell types in the cochlear nucleus-seven in the ventral cochlear nucleus and two in the dorsal cochlear nucleus-are described in this review. Globular bushy cells and two types of spherical bushy cells project to nuclei in the superior olivary complex that play roles in sound localization based on binaural cues. Octopus cells convey precisely timed information to nuclei in the superior olivary complex and lateral lemniscus that, in turn, send inhibitory input to the inferior colliculus. Cochlear root neurons send widespread projections to areas of the reticular formation involved in startle reflexes and autonomic functions. Type I multipolar cells may encode complex features of natural stimuli and send excitatory projections directly to the inferior colliculus. Type II multipolar cells send inhibitory projections to the contralateral cochlear nuclei. Fusiform cells in the dorsal cochlear nucleus appear to be important for the localization of sounds based on spectral cues and send direct excitatory projections to the inferior colliculus. Giant cells in the dorsal cochlear nucleus also project directly to the inferior colliculus; some of them may convey inhibitory inputs to the contralateral cochlear nucleus as well.

Animals↗

PubMed2002

Transformations in processing interaural time differences between the superior olivary complex and inferior colliculus: beyond the Jeffress model.

Interaural time differences (ITDs) are used to localize sounds and improve signal detection in noise. Encoding ITDs in neurons depends on specialized mechanisms for comparing inputs from the two ears. Most studies have emphasized how the responses of ITD-sensitive neurons are consistent with the tenets of the Jeffress model. The Jeffress model uses neuronal coincidence detectors that compare inputs from both sides and delay lines so that different neurons achieve coincidence at different ITDs. Although Jeffress-type models are successful at predicting sensitivity to ITDs in humans, in many respects they are a limited representation of the responses seen in neurons. In the superior olivary complex (SOC), ITD-sensitive neurons are distributed across both the medial (MSO) and lateral (LSO) superior olives. Similar response types are found in neurons sensitive to ITDs in two signal types: low-frequency sounds and envelopes of high-frequency sounds. Excitatory-excitatory interactions in the MSO are associated with peak-type responses, and excitatory-inhibitory interactions in the LSO are associated with trough-type responses. There are also neurons with responses intermediate between peak- and trough-type. In the inferior colliculus (IC), the same basic types remain, presumably due to inputs arising from the MSO and LSO. Using recordings from the SOC and IC, we describe how the response types can be described within a continuum that extends to very large values of ITD, and compare the functional organization at the two levels.

Acoustic Stimulation↗

PubMed2000

Improved auditory spatial sensitivity in near-sighted subjects.

There is a great deal of anecdotal and empirical evidence in favor of compensatory plasticity of the sensorial modalities when one of them undergoes a total deficit. Yet, while most research has focused on the development of spatial hearing in totally blind individuals, there are few works dealing with auditory compensation in the case of a partial visual deprivation. In the present study, three experiments show that subjects undergoing a visual deficit like myopia are more accurate at localizing sounds than normal-sighted subjects.

Acoustic Stimulation↗

PubMed1993

Tracking of "moving" fused auditory images by children.

Recent investigations (Cranford, Boose, & Moore, 1990a,b; Moore, Cranford, & Rahn, 1990) studied the ability of normal adult subjects to localize sounds under conditions that elicit the Precedence Effect. In different tests, subjects were required either to report the perceived location of a stationary fused auditory image (FAI) or track the apparent motion of a "moving" FAI. Movement of the FAI was simulated by incrementally varying the delay between pairs of clicks presented, one each, from two matched loudspeakers placed on opposite sides of the listener. In the present study, groups of normally developing children, ranging in age from 6 to 12 years of age, were tested with these two procedures. Although subjects performed at normal adult levels with the stationary FAI test, a significant age-related trend was observed with the moving FAI test. The younger children exhibited poorer tracking performances than did the older children. These results provide evidence that significant changes in binaural temporal processing abilities may occur in the early childhood years.

Acoustic Stimulation↗

PubMed1991

A blind mobility aid modeled after echolocation of bats.

A new model of a mobility aid for the blind was designed using microprocessor and ultrasonic devices. This mobility aid was evaluated based on psychophysical experiments. In this model, a downswept FM ultrasound signal is emitted from a transmitting array with broad directional characteristics in order to detect obstacles. The ultrasound reflections from the obstacles are picked up by a two-channel receiver. The frequency of the emitted ultrasound is swept from 70 to 40 kHz within 1 ms, so it has almost the same characteristics as the ultrasound a bat produces for echolocation. The frequency of the reflected ultrasound wave is down converted by about 50:1 by using a microcomputer with A/D and D/A converters. These audible waves are then presented binaurally through earphones. In this method obstacles may be perceived as localized sound images corresponding to the direction and the size of the obstacles. From the results of psychophysical experiments, it was found that downswept FM ultrasound was superior for the recognition of small obstacles compared to other ultrasonic schemes. With it a blind person can recognize a 1-mm-diameter wire. It was also proved that the blind could discriminate between several obstacles at the same time without any virtual images. This mobility aid, modeled after the bat's echolocation system, is very effective at detecting small obstacles placed in front of the head.

Animals↗

PubMed1994

Phase-locked response characteristics of single neurons in the frog "cochlear nucleus" to steady-state and sinusoidal-amplitude-modulated tones.

1. We made extracellular recordings from 164 single neurons in the frog dorsal medullary nucleus (DMN), a homologue of the cochlear nucleus. Phase-locked responses to tones at the unit's characteristic frequency (CF) and to off-CF tones were evaluated. We also stimulated units with tones at CF that were amplitude modulated sinusoidally between 5 and 1,000 Hz and examined responses to these stimuli. 2. Results showed that single neurons in the frog DMN displayed phase-locked discharges to tones at frequencies < or = 800 Hz. Phase-locking was robust at low frequencies (< 400 Hz) and became poorer at higher frequencies; the variation of the synchronization coefficient (SC) with frequency typically showed a low-pass characteristic. 3. The capacity of phase-locking to tones was correlated with the functional classification of a DMN neuron and the firing rate of its CF response. Primarylike neurons exhibited various degrees of phase-locked discharges to tones at off-CF frequencies. The average upper cutoff frequency, i.e., the frequency at which the SC dropped to 0.5 of maximum value, differed for the three classes of primarylike neurons. The average cutoff frequency was respectively 183, 325, and 536 Hz for primarylike neurons that displayed low (PL-1), intermediate (PL-2), and high (PL-3) steady-state firing rates to CF stimulation. The phasic neurons showed poor phase-locking capacities at all tone frequencies. 4. The frequency range of phase-locking to amplitude-modulated stimuli was also different for the different cell types, as evidenced by the units' modulation transfer functions (MTFs). The primarylike neurons exhibited mostly all-pass or low-pass sync-based MTFs. The mean upper cutoff frequencies for primarylike neurons having low-pass MTFs were 155 Hz for PL-1 neurons, 176 Hz for PL-2 neurons, and 218 Hz for PL-3 neurons. Pauser, chopper, phasic, and phasic-burst neurons gave mostly low-pass MTFs having a mean upper cutoff frequency of 219, 235, 242, and 251 Hz, respectively. 5. The phase-locking ability of DMN neurons to tones and to amplitude-modulated stimuli are compared with those of frog's primary afferent fibers and with those of avian and mammalian cochlear nucleus neurons. The significance of results in terms of sound localization and sound pattern recognition is discussed.

Animals↗

PubMed1999

Kinematics of eye movements of cats to broadband acoustic targets.

Operant conditioning was used to train cats with their heads immobilized to localize sound by directing their eyes to the location of the sources. The kinematics of those eye movements were studied and compared with eye movements to visual targets at the same locations. The main finding of this study is that eye movements to broadband long-duration acoustic targets have two components: an initial slow phase of variable duration and a fast, normal saccade. The slow component is characterized by a persistent, shallow velocity ramp, while the saccadic component of the response falls on the main sequence computed from eye movements to visual targets. The slow component was shorter before saccades to long-duration stimuli performed under the delayed-saccade task and practically absent before saccades to transient acoustic stimuli. The results suggest that the initial slow component is used by cats to deal with uncertainty associated with the location of long-duration broadband targets and that the input to the saccade integrator(s) is similar under both visual and acoustic conditions.

Acoustic Stimulation↗

PubMedDate not supplied

An approach to the development of hearing standards for hearing-critical jobs.

Many jobs at the Department of Fisheries and Oceans Canada (DFO) have several features in common: they are often performed in noisy environments and involve a number of auditory skills and abilities, such as speech communication, sound localization, and sound detection. If an individual lacks these skills and abilities, it may constitute a safety risk for this individual, as well as for fellow workers and the general public. A number of scientific models have been developed to predict performance on these auditory skills based on diagnostic measures of hearing such as pure-tone audiograms. While these models have significant scientific and research value, they are unable to provide accurate predictions of real life performance on auditory skills necessary to perform hearing-critical jobs. An alternative and more accurate approach has been developed in this research project. A direct measure of functional speech perception in noise (Hearing in Noise Test: HINT) has been identified and validated for use in screening applicants for hearing-critical jobs in DFO. This screening tool has adequate and well-defined psychometric properties (e.g. reliability, sensitivity, and validity) so that screening test results can be used to predict an individual's ability to perform critical auditory skills in noisy environments, with a known degree of prediction error. Important issues must be considered when setting screening criteria. First, the concept of hearing-critical tasks must be reviewed, since these tasks are often performed in high noise levels where normally-hearing people cannot hear adequately. Second, noise-induced hearing loss is frequent in these noisy environments, and workers who acquire a hearing loss might not continue to meet the minimal auditory screening criteria throughout their career. Other senses (e.g., vision, touch) also play an important role in these environments. Third, adaptation strategies have to be considered when recruits or incumbents fail the screening test.

Adult↗

PubMed2000

Plasticity in the neural coding of auditory space in the mammalian brain.

Sound localization relies on the neural processing of monaural and binaural spatial cues that arise from the way sounds interact with the head and external ears. Neurophysiological studies of animals raised with abnormal sensory inputs show that the map of auditory space in the superior colliculus is shaped during development by both auditory and visual experience. An example of this plasticity is provided by monaural occlusion during infancy, which leads to compensatory changes in auditory spatial tuning that tend to preserve the alignment between the neural representations of visual and auditory space. Adaptive changes also take place in sound localization behavior, as demonstrated by the fact that ferrets raised and tested with one ear plugged learn to localize as accurately as control animals. In both cases, these adjustments may involve greater use of monaural spectral cues provided by the other ear. Although plasticity in the auditory space map seems to be restricted to development, adult ferrets show some recovery of sound localization behavior after long-term monaural occlusion. The capacity for behavioral adaptation is, however, task dependent, because auditory spatial acuity and binaural unmasking (a measure of the spatial contribution to the "cocktail party effect") are permanently impaired by chronically plugging one ear, both in infancy but especially in adulthood. Experience-induced plasticity allows the neural circuitry underlying sound localization to be customized to individual characteristics, such as the size and shape of the head and ears, and to compensate for natural conductive hearing losses, including those associated with middle ear disease in infancy.

Adaptation, Physiological↗

PubMed2003

Sound recognition and localization in man: specialized cortical networks and effects of acute circumscribed lesions.

Functional imaging studies have shown that information relevant to sound recognition and sound localization are processed in anatomically distinct cortical networks. We have investigated the functional organization of these specialized networks by evaluating acute effects of circumscribed hemispheric lesions. Thirty patients with a primary unilateral hemispheric lesion, 15 with right-hemispheric damage (RHD) and 15 with left-hemispheric damage (LHD), were evaluated for their capacity to recognise environmental sounds, to localize sounds in space and to perceive sound motion. One patient with RHD and 2 with LHD had a selective deficit in sound recognition; 3 with RHD a selective deficit in sound localization; 2 with LHD a selective deficit in sound motion perception; 4 with RHD and 3 with LHD a combined deficit of sound localization and motion perception; 2 with RHD and 1 with LHD a combined deficit of sound recognition and motion perception; and 1 with LHD a combined deficit of sound recognition, localization and motion perception. Five patients with RHD and 6 with LHD had normal performance in all three domains. Deficient performance in sound recognition, sound localization and/or sound motion perception was always associated with a lesion that involved the shared auditory structures and the specialized What and/or Where networks, while normal performance was associated with lesions within or outside these territories. Thus, damage to regions known to be involved in auditory processing in normal subjects is necessary, but not sufficient for a deficit to occur. Lesions of a specialized network was not always associated with the corresponding deficit. Conversely, specific deficits tended not be associated predominantly with lesions of the corresponding network; e.g. deficits in auditory spatial tasks were observed in patients whose lesions involved to a larger extent the shared auditory structures and the specialized What network than the specialized Where network, and deficits in sound recognition in patients whose lesions involved mostly the shared auditory structures and to a varying degree the specialized What network. The human auditory cortex consists of functionally defined auditory areas, whose intrinsic organization is currently not understood. In particular, areas involved in the What and Where pathways can be conceived as: (1) specialized regions, in which lesions cause dysfunction limited to the damaged part; observed deficits should be then related to the specialization of the damaged region and their magnitude to the extent of the damage; or (2) specialized networks, in which lesions cause dysfunction that may spread over the two specialized networks; observed deficits may then not be related to the damaged region and their magnitude not proportional to the extent of the damage. Our results support strongly the network hypothesis.

Acute Disease↗

PubMedDate not supplied

[Role of auditory regions of the cerebral cortex in localizing stationary sound sources in the dog].

The role of the auditory cortex in the localization of stationary sources was deduced from the deficit of localization ability of decorticated dogs. The lateralization threshold for stimulation by signals with interaural difference in time (delta T) and intensity (delta I) was taken as a quantitative estimate of the localization ability. These thresholds were determined for intact animals as well as for those with uni- and bilateral removal of the auditory cortex (AI, AII, Ep). The bilateral ablation has been found to disturb the temporal cue localization, whereas the delta I-cue localization has been retained. The ability of localization by the temporal cue depended on damage size (AI). The obtained data imply the importance of the auditory cortex for perception of temporal signal characteristics.

Animals↗

PubMed1992

Localization of sound in the vertical plane with and without high-frequency spectral cues.

Binaural localization of 3.0-kHz high- and lowpass noise presented in the median vertical plane (MVP) and lateral vertical plane (LVP) was investigated. We anticipated superior performance when localizing the highpass noise by virtue of the availability of pinna cues. The viability of this supposition was strengthened by monaural localization tests in which performance proficiency for the highpass noise exceeded that for the lowpass noise (p less than .01). The main result showed that binaural localization of proficiency for highpass noise surpassed that for lowpass noise for all listening conditions (p less than .01). However, the importance of binaural temporal and level differences in vertical-plane localization was demonstrated by the highly respectable performances when the lowpass noise was presented in the LVP. Data from binaural localization in the MVP and monaural localization in the LVP suggested that the influence of pinna cues diminishes for source elevations above 45 degrees.

Adult↗

PubMed2004

Effects of intensity and location on sound location discrimination in macaque monkeys.

Sound localization performance is degraded at low stimulus intensities in humans, and while the sound localization ability of humans and macaque monkeys appears similar, the effects of intensity have yet to be described in the macaque. We therefore defined the ability of four macaque monkeys to localize broadband noise stimuli at four different absolute intensities and six different starting locations in azimuth. Results indicate that performance was poorest at the lowest intensity tested (25 dB SPL), intermediate at 35 dB SPL, and equivalent at 55 and 75 dB SPL. Localization performance was best at 0 degree (directly in front of the animal) and was systematically degraded at more peripheral locations (+/-30 degrees and 90 degrees) and worst at a location directly behind the animal. Reaction times showed the same trends, with reaction times increasing with decreasing stimulus intensity, even under conditions where the monkey discriminated the location change with the same performance. These results indicate that sound level as well as position profoundly influences sound localization ability.

Acoustic Stimulation↗