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PubMed1989

On listening where we look: the fragility of a phenomenon.

The role of eye position information has been the subject of some debate in the literature on the visual facilitation of auditory localization and attention. In one particularly compelling study, Reisberg, Scheiber, and Potemken (1981) found that fixation position strongly influenced subjects' recall performance in a binaural selective-listening task. The present paper describes repeated failures to demonstrate the eye position effect under conditions similar to those of the original study, thus challenging the robustness of this oft-cited phenomenon of "listening where we look."

Adult↗
PubMed1982

The problem of front-back localization in binaural hearing.

Some investigations concerning the problem of front-back discrimination in normal hearing are described. Three groups of experiments are included: Some objective measurements of transfer functions of the ears of four subjects, horizontal plane simulations and modifications of artificial-head signals in order to bring about directional inversions in the horizontal plane. It is concluded that subjects are able to utilize small individual characteristics in the transfer functions of their own outer ears to distinguish between front and back.

Adult↗
PubMed1996

Acoustic reflectivity of a dolphin.

Backscatter measurements were made on a stationary Atlantic bottlenosed dolphin under controlled conditions. Three sets of measurements were made: (1) broadside aspect target strength as a function of frequency from 23 to 80 kHz; (2) relative target strength as a function of the polar angle about the animal using a short click signal having a peak frequency of 67 kHz; and (3) relative reflective strength of different portions of the animal's body. The mean target strength at the broadside aspect decreased from -11 to -24 dB as the frequency increased from 23 to 45 kHz. As the frequency increased from 45 kHz, the target strength rose to a local maximum of -18 dB at 66 kHz and then decreased to -23 dB at 79 kHz. Maximum target strength was measured at the broadside aspect and exceeded the minimum (tail aspect) target strength by 21 dB. The target strength at the head aspect was 5 dB below that of the broadside aspect. Most acoustic energy was reflected from the area between the dorsal and pectoral fins, corresponding to the location of the dolphin's lungs.

Animals↗
PubMedDate not supplied

Exploring the benefits of bilateral cochlear implants.

Several recent reports indicate that both localization and speech intelligibility in spatially separated noise are substantially improved by using cochlear implants (CIs) in both ears rather than in just one. Benefits appear to be largely derived from the effects of level variations at the two ears due to the head shadow whereas contributions from interaural time differences (ITDs) seem smaller than in normal hearing listeners. The effect of binaural unmasking estimated from speech studies to date varies from study to study and is possibly confounded by issues such as listening experience, bias or loudness effects when comparing the performance for the better ear with that using both ears. To improve the contribution from timing information at the two ears, it may be necessary to change present clinical sound-processing schemes that currently preserve only envelope cues so that they also preserve fine-timing information. However, recently published data show that basic psychophysical sensitivity to fine-timing ITDs in CI patients is very poor for rates beyond a few hundred hertz, suggesting that subjects do not actually hear ITD cues at those rates anyway. Data from a number of new studies are presented to discuss these and other issues related to the potential to benefit from bilateral implantation.

Cochlear Implants↗
PubMed2001

Using conjoint analysis to examine the importance of hearing aid attributes.

OBJECTIVE: To introduce conjoint analysis (CA) as a method to explain choice decisions of hearing aid users and to measure the contributions of different hearing aid attributes involved. DESIGN: The study was conducted using CA, a method that is well established in marketing, but has not been used for hearing aid research. CA examines the contributions (importance) various attributes make to overall preference judgements. It is based on the premises that objects (i.e., hearing aids) can be described as different combinations of several attributes. The relative importance of the attributes is estimated from integral judgements of hypothetical hearing aids. The advantages of CA are a more realistic presentation of complete products instead of isolated attributes and the consideration of trade-offs between the features. The following attributes selected from 12 features in a prestudy were included in the application: speech perception in quiet, speech perception in noise, handling, sound quality, localization, and feedback. 93 randomly chosen experienced hearing aid wearers participated in the survey. RESULTS: It was found that the attributes concerning speech perception were by far most important. Speech discrimination in quiet and in noise were almost equally significant and contributed with 56% to the preference decisions of the subjects. The remaining attributes showed values in the range of 10% to 12%. When comparing various subgroups dependent on age, sex, hearing loss, satisfaction, etc., significant differences concerning the preferences were found. Elder and female subjects attached greater importance of the attribute "handling" whereas younger patients judged "speech in noise" more important. In general, subjects with greater hearing loss considered speech intelligibility in quiet to be more important than in noisy surroundings. Moreover, sound quality seems to be a significant indicator for satisfaction with the hearing aid. CONCLUSIONS: This study proposes CA as a survey technique to examine individual preferences for hearing aids. Several assumptions about the importance of hearing aid features for different groups of users could be confirmed quantitatively. Segmentation showed valid results depending on socio-demographic and user-specific parameters. The method used and the results are of interest for audiologists as well as the hearing aid industry. They provide valuable tools for future hearing aid design and should be considered in the development of self-assessment inventories.

Correction of Hearing Impairment↗
PubMed1993

Overcoming the right-ear advantage: a study of focused attention in children.

Several studies indicate that normal right-handed children of various ages show a right-ear advantage (REA) for dichotic verbal stimuli even when instructed to attend to the left ear. Other evidence, however, suggests that selective listening ability begins to develop in early childhood and that children reliably can overcome the REA by the age of 8 or 9 years. We used a signal detection procedure to address this apparent contradiction. In the first of two experiments, 58 children in two age groups (M = 7 and 10 years) were able to overcome the REA for dichotic consonant-vowel (CV) stimuli when instructed to focus attention on the left ear. Success in detecting and localizing signals from the left ear, as reflected in hit rates, was independent of age and reading level. A second experiment, in which strings of dichotic monosyllabic words were presented to 56 children at the same two age levels, yielded similar results. These findings challenge the claim that ability to overcome the REA when attending to the left ear reflects an abnormality of cerebral functioning.

Attention↗
PubMed1989

Headphone simulation of free-field listening. II: Psychophysical validation.

Listeners reported the apparent spatial positions of wideband noise bursts that were presented either by loudspeakers in free field or by headphones. The headphone stimuli were digitally processed with the aim of duplicating, at a listener's eardrums, the waveforms that were produced by the free-field stimuli. The processing algorithms were based on each subject's free-field-to-eardrum transfer functions that had been measured at 144 free-field source locations. The headphone stimuli were localized by eight subjects in virtually the same positions as the corresponding free-field stimuli. However, with headphone stimuli, there were more front-back confusions, and source elevation seemed slightly less well defined. One subject's difficulty with elevation judgments, which was observed both with free-field and with headphone stimuli, was traced to distorted features of the free-field-to-eardrum transfer function.

Acoustic Stimulation↗
PubMed1999

Sensory experience and the formation of a computational map of auditory space in the brain.

The basic wiring of the brain is first established before birth by using a variety of molecular guidance cues. These connections are then refined by patterns of neural activity, which are initially generated spontaneously and subsequently driven by sensory experience. In the superior colliculus, a midbrain nucleus involved in the control of orienting behaviour, visual, auditory, and tactile inputs converge to form superimposed maps of sensory space. Maps of visual space and of the body surface arise from spatially ordered projections from the retina and skin, respectively. In contrast, the map of auditory space is computed within the brain by tuning the neurons to different localization cues that result from the acoustical properties of the head and ears. Establishing and maintaining the registration of the maps in the face of individual differences in the size and relative positions of different sense organs is an activity-dependent process in which the synaptic circuits underlying the auditory representation are modified and calibrated under the influence of both auditory and visual experience. BioEssays 1999;21:900-911.

Animals↗
PubMed1996

Newly learned auditory responses mediated by NMDA receptors in the owl inferior colliculus.

Alignment of auditory and visual receptive fields in the optic tectum of the barn owl (Tyto alba) is maintained through experience-dependent modification of auditory responses in the external nucleus of the inferior colliculus (ICX), which provides auditory input to the tectum. Newly learned tectal auditory responses, induced by altered visual experience, were found to be pharmacologically distinct from normal responses expressed at the same tectal sites. N-methyl-D-aspartate (NMDA) receptor antagonists administered systemically or applied locally in the ICX reduced learned responses more than normal responses. This differential blockade was not observed with non-NMDA or broad-spectrum antagonists. Thus, NMDA receptors preferentially mediate the expression of novel neuronal responses induced by experience during development.

2-Amino-5-phosphonovalerate↗
PubMed2006

A positron emission tomography study during auditory localization by late-onset blind individuals.

Individuals deprived of vision early in life often demonstrate exceptional abilities in their remaining sensory modalities in order to compensate for their handicap. Recent studies have shown that some of these abilities also extend to those who have lost their sight later in life. It is not clear, however, what mechanisms underlie these abilities. Here, we examined cortical activation using positron emission tomography in late-onset blind participants during a free-field auditory localization task. Even though no behavioral enhancements were observed in this testing condition relative to sighted controls, the results revealed that the occipital cortex was nonetheless activated during task execution. We conclude that late-onset blind individuals do manifest cerebral reorganization, although its functional relevance to the task is less clear.

Acoustic Stimulation↗
PubMed2005

Echolocation, vocal learning, auditory localization and the relative size of the avian auditory midbrain nucleus (MLd).

The avian nucleus mesencephalicus lateralis, pars dorsalis (MLd) is an auditory midbrain nucleus that plays a significant role in a variety of acoustically mediated behaviours. We tested whether MLd is hypertrophied in species with auditory specializations: owls, the vocal learners and echolocaters. Using both conventional and phylogenetically corrected statistics, we find that the echolocating species have a marginally enlarged MLd, but it does not differ significantly from auditory generalists, such as pigeons, raptors and chickens. Similarly, all of the vocal learners tend to have relatively small MLds. Finally, MLd is significantly larger in owls compared to all other birds regardless of how the size of MLd is scaled. This enlargement is far more marked in asymmetrically eared owls than symmetrically eared owls. Variation in MLd size therefore appears to be correlated with some auditory specializations, but not others. Whether an auditory specialist possesses a hypertrophied MLd appears to be depend upon their hearing range and sensitivity as well as the ability to resolve small azimuthal and elevational angles when determining the location of a sound. As a result, the only group to possess a significantly large MLd consistently across our analyses is the owls. Unlike other birds surveyed, owls have a battery of peripheral and other central auditory system specializations that correlate well with their hearing abilities. The lack of differences among the generalists, vocal learners and echolocaters therefore reflects an overall similarity in hearing abilities, despite the specific life history requirements of each specialization and species. This correlation between the size of a neural structure and the sensitivity of a perceptual domain parallels a similar pattern in mammals.

Analysis of Variance↗
PubMed2005

Auditory compensation in myopic humans: involvement of binaural, monaural, or echo cues?

The purpose of this paper is to investigate the involvement of various auditory localization mechanisms in the improvement of auditory spatial sensitivity in the case of partial visual deprivation. We compared sensitivity to binaural, monaural, and echo cues between normal-sighted and myopic subjects. In an auditory task, which depended solely upon binaural processing, myopic and normal-sighted subjects showed an almost equal localization performance. We also found that myopic subjects were no more disturbed than normal-sighted subjects when spectral shape cues were removed. On the other hand, near-sighted subjects exhibited better echolocation skills and a higher sensitivity to echo cues than normal-sighted subjects. We can therefore conclude that an improved auditory spatial sensitivity in myopic subjects may result from the increased use of echo information.

Acoustic Stimulation↗
PubMed1998

Sequential source of the M100 exhibits inter-hemispheric asymmetry.

The most prominent auditory evoked field component occurs at about 100 ms latency and is termed the M100. We recorded M100 data from 20 subjects, in both hemispheres. We modeled the generators with a single equivalent current dipole in a 10 ms sliding window from 0 to 245 ms post-stimulus. A residual error curve was plotted, and a search for local minima identified two latencies at about 75 and 100 ms. In the left hemisphere, the early generator was about 6 mm above the later source; in the right hemisphere the early source was about 3 mm above the later, and 11 mm posterior. The M100 is a compound source, and the model may provide additional information in cases with reported laterality differences.

Acoustic Stimulation↗
PubMed1981

Evaluation of binaural hearing aids in children using localization and speech intelligibility tasks.

Because of an assumed relationship between localization and speech intelligibility in noise it has been suggested that a localization test provides a suitable measure for the evaluation of binaural aids in everyday situations. The present study shows a significant correlation (a) between binaural advantage in a localization task and the binaural advantage in speech intelligibility in noise task, and (b) between binaural advantage in judgement of separation of speech and noise and binaural advantage in a speech intelligibility in noise task. However, neither relationship was strong enough for accurate individual prediction of binaural advantages in speech intelligibility. Possible reasons for this are discussed, and the lines that further research might follow are suggested.

Adolescent↗
PubMed1982

Binaural interaction and localization with various hearing impairments.

Binaural interaction and localization abilities of hearing-impaired listeners are summarized separately for each of several types of hearing and neurological disorders. The dependence of binaural abilities on the nature of the impairment is emphasized. Unfortunately, available data are not sufficient to characterize the specific aspects of the stimulus information available in each type of impairment.

Auditory Perception↗
PubMed2003

Localization of the event-related potential novelty response as defined by principal components analysis.

Recent research indicates that novel stimuli elicit at least two distinct components, the Novelty P3 and the P300. The P300 is thought to be elicited when a context updating mechanism is activated by a wide class of deviant events. The functional significance of the Novelty P3 is uncertain. Identification of the generator sources of the two components could provide additional information about their functional significance. Previous localization efforts have yielded conflicting results. The present report demonstrates that the use of principal components analysis (PCA) results in better convergence with knowledge about functional neuroanatomy than did previous localization efforts. The results are also more convincing than that obtained by two alternative methods, MUSIC-RAP and the Minimum Norm. Source modeling on 129-channel data with BESA and BrainVoyager suggests the P300 has sources in the temporal-parietal junction whereas the Novelty P3 has sources in the anterior cingulate.

Acoustic Stimulation↗
PubMed2000

Interactions between exogenous auditory and visual spatial attention.

Six experiments were carried out to investigate the issue of cross-modality between exogenous auditory and visual spatial attention employing Posner's cueing paradigm in detection, localization, and discrimination tasks. Results indicated cueing in detection tasks with visual or auditory cues and visual targets but not with auditory targets (Experiment 1). In the localization tasks, cueing was found with both visual and auditory targets. Inhibition of return was apparent only in the within-modality conditions (Experiment 2). This suggests that it is important whether the attention system is activated directly (within a modality) or indirectly (between modalities). Increasing the cue validity from 50% to 80% influenced performance only in the localization task (Experiment 4). These findings are interpreted as being indicative for modality-specific but interacting attention mechanisms. The results of Experiments 5 and 6 (up/down discrimination tasks) also show cross-modal cueing but not with visual cues and auditory targets. Furthermore, there was no inhibition of return in any condition. This suggests that some cueing effects might be task dependent.

Adult↗
PubMed2002

Patients utilizing a hearing aid and a cochlear implant: speech perception and localization.

OBJECTIVE: The purpose of this pilot study was to document speech perception and localization abilities in patients who use a cochlear implant in one ear and a hearing aid in the other ear. DESIGN: We surveyed a group of 111 cochlear implant patients and asked them whether they used a hearing aid on their unimplanted ear. The first three patients who were available were tested on word and sentence recognition and localization tasks. Speech stimuli were presented from the front in quiet and in noise. In the latter conditions, noise was either from the front, the right, or the left. Localization was tested with noise bursts presented at 45 degrees from the right or left. In addition we asked the patients about their abilities to integrate the information from both devices. RESULTS: Speech perception tests in quiet showed a binaural advantage for only one of the three patients for words and none for sentences. With speech and noise both in front of the patient, two patients performed better with both devices than with either device alone. With speech in front and noise on the hearing aid side, no binaural advantage was seen, but with noise on the cochlear implant side, one patient showed a binaural advantage. Localization ability improved with both devices for two patients. The third patient had above-chance localization ability with his implant alone. CONCLUSIONS: A cochlear implant in one ear and a hearing aid in the other ear can provide binaural advantages. The patient who did not show a clear binaural advantage had the poorest hearing aid alone performance. The absolute and relative levels of performance at each ear are likely to influence the potential for binaural integration.

Cochlear Implants↗