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PubMed1998

Adapting to supernormal auditory localization cues. II. Constraints on adaptation of mean response.

A series of experiments was performed in which subjects were trained to interpret auditory localization cues arising from locations different from their normal spatial positions. The exact pattern of mean response to these alterations (as a function of time) was examined in order to begin to develop a quantitative model of adaptation. Mean responses were roughly proportional to the normal position associated with the localization cues presented. As subjects adapted, the best-fit slope (relating mean response and normal position) changed roughly exponentially with time. The exponential rate and adaptation asymptote were found for each subject in each experiment, as well as the rate and asymptote of readaptation to normal cues. The rate of adaptation does not show any statistical dependence on experimental conditions; however, the asymptote of the best-fit slope varied with the strength of the transformation used in each experiment. This result is consistent with the hypothesis that subjects cannot adapt to a nonlinear transformation of auditory localization cues, but instead adapt to a linear approximation of the transformation. Over time, performance changes exponentially towards the best-fit linear approximation for the transformation used in a particular experiment, and the rate of this adaptation does not depend upon the transformation employed.

Auditory Perception↗
PubMed1993

Supernormal auditory localization. I. General background.

In this series of papers, we consider human auditory localization and how its deficiencies can be reduced by appropriate processing and coding of acoustical signals in teleoperator and virtual-environment systems. Attention is given to how localization cues can be altered to improve the just-noticeable-difference (JND) in spatial position and to phenomena related to the use of such altered localization cues for the identification of spatial position. Unlike most current studies of synthetic auditory localization, our study includes consideration of distance as well as direction. In this first paper of the series, we provide general background material. In subsequent papers, we will present a variety of empirical results.

Auditory Perception↗
PubMed1993

Organization of response areas in ferret primary auditory cortex.

1. We studied the topographic organization of the response areas obtained from single- and multiunit recordings along the isofrequency planes of the primary auditory cortex in the barbiturate-anesthetized ferret. 2. Using a two-tone stimulus, we determined the excitatory and inhibitory portions of the response areas and then parameterized them in terms of an asymmetry index. The index measures the balance of excitatory and inhibitory influences around the best frequency (BF). 3. The sensitivity of responses to the direction of a frequency-modulated (FM) tone was tested and found to correlate strongly with the asymmetry index of the response areas. Specifically, cells with strong inhibition from frequencies above the BF preferred upward sweeps, and those from frequencies below the BF preferred downward sweeps. 4. Responses to spectrally shaped noise were also consistent with the asymmetry of the response areas. For instance, cells that were strongly inhibited by frequencies higher than the BF responded best to stimuli that contained least spectral energy above the BF, i.e., stimuli with the opposite asymmetry. 5. Columnar organization of the response area types was demonstrated in 66 single units from 16 penetrations. Consistent with this finding, it was also shown that response area asymmetry measured from recordings of a cluster of cells corresponded closely with those measured from its single-unit constituents. Thus, in a local region, most cells exhibited similar response area types and other response features, e.g., FM directional sensitivity. 6. The distribution of the asymmetry index values along the isofrequency planes revealed systematic changes in the symmetry of the response areas. At the center, response areas with narrow and symmetric inhibitory sidebands predominated. These gave way to asymmetric inhibition, with high-frequency inhibition (relative to the BF) becoming more effective caudally and low-frequency inhibition more effective rostrally. These response types tended to cluster along repeated bands that paralleled the tonotopic axis. 7. Response features that correlated with the response area types were also mapped along the isofrequency planes. Thus, in four animals, a map of FM directional sensitivity was shown to be superimposed on the response area map. Similarly, it was demonstrated in six animals that the spectral gradient of the most effective noise stimulus varied systematically along the isofrequency planes. 8. One functional implication of the response area organization is that cortical responses encode the locally averaged gradient of the acoustic spectrum by their differential distribution along the isofrequency planes. This enhances the representation of such features as the symmetry of spectral peaks and edges and the spectral envelope.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1981

Binaural interaction of impaired listeners. A review of past research.

This paper reviews past studies of binaural interaction in impaired listeners. The topics covered include localization and lateralization; equal loudness, centering and lateralization adaptation; detection of signals in noise; and discrimination of interaural time delay and interaural amplitude ratio. Comments concerning experimental design and procedures, as well as interpretation of results, are often included with descriptions of the studies.

Auditory Perception↗
PubMed1991

Auditory localization under conditions of unilateral fitting of different hearing aid systems.

The spatial localization function of hearing-impaired listeners, usually fitted bilaterally with BTE, ITE or ITC devices, was tested under conditions of unilateral fitting of each of their own hearing aids, and unilateral fitting of stock versions of each of the other types. For the BTE wearers average localization accuracy and individual variability were not greatly changed when wearing only their left ear device, compared with bilateral aided performance. In ITE wearers, unilateral fitting in either ear led to somewhat poorer performance than bilateral. In the ITC wearers unilateral fitting produced inconsistent outcomes. Both BTE and ITE wearers fared poorly when fitted unilaterally with stock forms of devices 'foreign' to them, whereas ITC wearers did not show such a contrasting outcome. A group of non-impaired listeners showed severe disruption of localization under unilateral BTE and ITC hearing aid conditions, and to a lesser extent with ITEs. Results for the hearing-impaired listeners are interpreted in terms of adaptation to different usage patterns, with BTE wearers suggested as having adapted to their own systems unilaterally as well as bilaterally.

Auditory Threshold↗
PubMed2006

"What" versus "where" in the audiovisual domain: an fMRI study.

Similar "what/where" functional segregations have been proposed for both visual and auditory cortical processing. In this fMRI study, we investigated if the same segregation exists in the crossmodal domain, when visual and auditory stimuli have to be matched in order to perform either a recognition or a localization task. Recent neuroimaging research highlighted the contribution of different heteromodal cortical regions during various forms of crossmodal binding. Interestingly, crossmodal effects during audiovisual speech and object recognition have been found in the superior temporal sulcus, while crossmodal effects during the execution of spatial tasks have been found over the intraparietal sulcus, suggesting an underlying "what/where" segregation. In order to directly compare the specific involvement of these two heteromodal regions, we scanned ten male right-handed subjects during the execution of two crossmodal matching tasks. Participants were simultaneously presented with a picture and an environmental sound, coming from either the same or the opposite hemifield and representing either the same or a different object. The two tasks required a manual YES/NO response respectively about location or semantic matching of the presented stimuli. Both group and individual subject analysis were performed. Task-related differences in BOLD response were observed in the right intraparietal sulcus and in the left superior temporal sulcus, providing a direct confirmation of the "what-where" functional segregation in the crossmodal audiovisual domain.

Acoustic Stimulation↗
PubMed1987

Response and reinforcement in operant audiometry.

Variable success in audiometric assessment of young children with operant conditioning indicates the need for systematic examination of commonly employed techniques. The current study investigated response and reinforcement features of two operant discrimination paradigms with normal 17-month-old children. Findings indicated more responses prior to the onset of habituation when the response task was based on complex central processing skills (localization and coordination of auditory/visual space) versus simple detection. Use of animation in toy reinforcers resulted in more than a twofold increase in the number of subject responses. Results showed no significant difference in response conditioning rate or consistency for the response tasks and forms of reinforcement examined.

Audiometry↗
PubMed1995

Preserved auditory spatial localization following cerebral hemispherectomy.

Auditory spatial function was assessed in six patients who had undergone unilateral cerebral hemispherectomy for the relief of intractable epilepsy. Separate localization and discrimination tests were carried out. In the first test, subjects localized the azimuthal position of a brief click presented at one of 13 positions in a free field, by pointing to its perceived position. All six patients demonstrated some preservation of localization ability, with some individual subjects performing at normal or near-normal levels. However, as a group, the patient sample localized less accurately than normal controls at extreme azimuthal positions, especially contralateral to the removal. In the second test, two clicks were presented either from the same location or from two locations separated by 30 degrees, and a same-different judgment was required. In this test the patient group performed worse than control subjects overall, but also demonstrated preserved discrimination ability in both hemifields. These findings demonstrate the expected existence of contralateral localization deficits, but the relative sparing of function contrasts with reports from animal behavioural studies, in which severe and persistent localization deficits contralateral to auditory cortex excision are described. Our findings suggest that extensive, early damage to one hemisphere may permit reorganization of function to occur, with auditory spatial ability being mediated by cortical systems in the remaining hemisphere and/or by subcortical structures.

Adult↗
PubMed2001

Expression of the Kv3.1 potassium channel in the avian auditory brainstem.

The Shaw-like potassium channel Kv3.1, a delayed rectifier with a high threshold of activation, is expressed in the time coding nuclei of the bird auditory brainstem. In both barn owls and chickens, Kv3.1 mRNA was expressed in the cochlear nucleus magnocellularis (NM) and the nucleus laminaris (NL). Western blot analysis showed that an antibody raised against the synthetic peptide sequence of rat Kv3.1 (rKv3.1) specifically recognized the same 92 kDa protein bands in both rat and chicken synaptosomal preparations. Immunohistochemical analyses using this anti-rKv3.1 antibody revealed a prominent gradient in Kv3.1 immunoreactivity along the tonotopic axis of the barn owl NM and NL and a less prominent gradient in the chicken. The precise localization of the Kv3.1 immunoproduct was resolved by electron microscopy. In both the owl and the chicken, Kv3.1 was targeted postsynaptically in NM and NL. The major difference in localization of Kv3.1 protein between the two birds was the expression of Kv3.1 in the NM axons and terminals in the region of the barn owl NL. This location of Kv3.1 channels supports its postulated function in reducing the width of action potentials as they invade the presynaptic terminal. The presynaptic localization may be a specialization for enabling neurons in owl NM to transmit high-frequency temporal information with little jitter.

Alternative Splicing↗
PubMed2006

Sparse representations for the cocktail party problem.

A striking feature of many sensory processing problems is that there appear to be many more neurons engaged in the internal representations of the signal than in its transduction. For example, humans have approximately 30,000 cochlear neurons, but at least 1000 times as many neurons in the auditory cortex. Such apparently redundant internal representations have sometimes been proposed as necessary to overcome neuronal noise. We instead posit that they directly subserve computations of interest. Here we provide an example of how sparse overcomplete linear representations can directly solve difficult acoustic signal processing problems, using as an example monaural source separation using solely the cues provided by the differential filtering imposed on a source by its path from its origin to the cochlea [the head-related transfer function (HRTF)]. In contrast to much previous work, the HRTF is used here to separate auditory streams rather than to localize them in space. The experimentally testable predictions that arise from this model, including a novel method for estimating the optimal stimulus of a neuron using data from a multineuron recording experiment, are generic and apply to a wide range of sensory computations.

Action Potentials↗
PubMed1991

Auditory localization in teleoperator and virtual environment systems: ideas, issues, and problems.

The increasing availability and use of advanced high-tech human-machine interfaces raise many interesting questions about what information should be presented to each sensory modality and how the information should be coded for a given modality. In this paper, attention is confined to the auditory component of the interface and, more specifically, to auditory localization. Both teleoperator systems and virtual-environment systems are considered, and attention is focused upon the opportunities and difficulties associated with the use of unnatural perceptual cues in these systems. Of central interest in this discussion is the use of such cues to improve resolution and thereby obtain systems with superlocalization capabilities.

Computer Simulation↗
PubMed2000

Who, what, where? Recognition and localization of acoustic signals by insects.

Insects, like all hearing animals, must analyze acoustic signals to determine both their content and their location. Neurophysiological experiments, together with behavioral tests, are beginning to reveal the mechanisms underlying these signal-analysis tasks. Work summarized here focusses on two issues: first, how insects analyze the temporal structure of a single signal in the presence of other competing signals; and second, how the signal's location is represented by the binaural difference in neural activity.

Animals↗
PubMed2004

Unifying multisensory signals across time and space.

The brain integrates information from multiple sensory modalities and, through this process, generates a coherent and apparently seamless percept of the external world. Although multisensory integration typically binds information that is derived from the same event, when multisensory cues are somewhat discordant they can result in illusory percepts such as the "ventriloquism effect." These biases in stimulus localization are generally accompanied by the perceptual unification of the two stimuli. In the current study, we sought to further elucidate the relationship between localization biases, perceptual unification and measures of a participant's uncertainty in target localization (i.e., variability). Participants performed an auditory localization task in which they were also asked to report on whether they perceived the auditory and visual stimuli to be perceptually unified. The auditory and visual stimuli were delivered at a variety of spatial (0 degrees, 5 degrees, 10 degrees, 15 degrees ) and temporal (200, 500, 800 ms) disparities. Localization bias and reports of perceptual unity occurred even with substantial spatial (i.e., 15 degrees ) and temporal (i.e., 800 ms) disparities. Trial-by-trial comparison of these measures revealed a striking correlation: regardless of their disparity, whenever the auditory and visual stimuli were perceived as unified, they were localized at or very near the light. In contrast, when the stimuli were perceived as not unified, auditory localization was often biased away from the visual stimulus. Furthermore, localization variability was significantly less when the stimuli were perceived as unified. Intriguingly, on non-unity trials such variability increased with decreasing disparity. Together, these results suggest strong and potentially mechanistic links between the multiple facets of multisensory integration that contribute to our perceptual Gestalt.

Acoustic Stimulation↗
PubMed1991

Localization of visual targets inside and outside the field of view: the effect of hearing loss.

In two experiments the eye and head localization responses of auditorially handicapped children to visual targets in a surrounding circular display were compared with the corresponding responses of age-matched controls (Experiment 1, mean age: 131 months, hearing loss of auditorially handicapped children greater than 90 dB; Experiment 2, two age groups with mean ages: 72 and 123 months, hearing loss of auditorially handicapped greater than 50 dB). It was hypothesized that an auditory deprivation results in a deficient spatial orientation to the regions outside the visual field. This in turn should affect the actual localization behaviour to visual targets situated within those regions. Differences between the auditorially handicapped and non-handicapped children were found with respect to the localization times of so-called 'reversal' responses of eye (Experiment 1) and head (Experiment 2) to targets situated outside the field of view. In the second experiment significant age-effects were present. The implications of these findings for the presence of specific differences in cognitive spatial abilities between auditorially handicapped and hearing children are discussed.

Age Factors↗
PubMed1988

Sensitivity and specificity of audiological tests in patients with vertigo.

In patients with vertigo a comprehensive test battery has been used for localizing pathological processes responsible for the symptoms. Audiological tests have been an integral part of the otoneurological investigation. However, in many studies the diagnostic sharpness of psychoacoustic tests in the localization of specific disease in the cranial nerve system has been called in question. Other tests, such as stapedius reflex and auditory brainstem response, have been of increasing importance in the diagnostic set-up. The purpose of this paper is to present a survey of the literature regarding the position of audiological tests in otoneurology.

Acoustic Impedance Tests↗
PubMed2005

Localization and speech-identification ability of hearing-impaired listeners using phase-preserving amplification.

OBJECTIVE: The purpose of these experiments was to determine the ability of hearing-impaired listeners to localize and to identify speech in noise using phase-preserving and non-phase-preserving amplification. DESIGN: These abilities were measured 4 times over each of two 16-week periods, using a randomized, single-blinded, within-subject crossover design. Listeners were fitted bilaterally, using the National Acoustic Laboratories linear frequency-gain characteristic with a digital hearing aid programmed in one of two ways: (1) with a linear-phase filter and (2) with filters designed to compensate for the magnitude and phase anomalies caused by the hearing aid fitting, thus preserving interaural phase. Listeners identified a word and its location in background noise with a speech-shaped spectrum. RESULTS: Immediately after fitting, both hearing aid programs reduced the listeners' ability to localize the speech in noise. The phase-preserving processing had a less detrimental effect on localization ability immediately after fitting. After 3 weeks, performance improved such that, for localization in noise, there was no detrimental effect of amplification and no difference between the two processing strategies. Over 16 weeks, speech understanding in noise improved. Speech understanding for phase-preserving processing was slightly and significantly better than linear-phase processing at 16 weeks. CONCLUSIONS: Localization ability using phase-preserving amplification does not differ from localization ability using traditional non-phase-preserving amplification after just 3 weeks of use. Listeners quickly acclimated to altered spatial cues. Phase-preserving amplification provided a 2.3% advantage for speech intelligibility in noise after 16 weeks.

Aged↗
PubMed2006

Some benefits and limitations of binaural cochlear implants and our ability to measure them.

We review new recognition and localization skills in patients using one or two cochlear implant(s). We observed one unilateral patient who showed localization performance above chance. We also provide evidence for binaural processing in bilateral cochlear implant patients, even when tested with speech from the front without noise. We unsuccessfully attempted to find correlations between localization and squelch, between these variables and pre-implant threshold differences, or these variables and post-implant recognition differences. We strongly believe that new tests are needed to examine the potential benefit of two implants. We describe three tests that we use to show a binaural advantage: cued recognition, movement direction, and recognition with multiple jammers.

Auditory Threshold↗
PubMed2000

Hair cell heterogeneity and ultrasonic hearing: recent advances in understanding fish hearing.

The past decade has seen a wealth of new data on the auditory capabilities and mechanisms of fishes. We now have a significantly better appreciation of the structure and function of the auditory system in fishes with regard to their peripheral and central anatomy, physiology, behaviour, sound source localization and hearing capabilities. This paper deals with two of the newest of these findings, hair cell heterogeneity and the detection of ultrasound. As a result of this recent work, we now know that fishes have several different types of sensory hair cells in both the ear and lateral line and there is a growing body of evidence to suggest that these hair cell types arose very early in the evolution of the octavolateralis system. There is also some evidence to suggest that the differences in the hair cell types have functional implications for the way the ear and lateral line of fishes detect and process stimuli. Behavioural studies have shown that, whereas most fishes can only detect sound to 1-3 kHz, several species of the genus Alosa (Clupeiformes, i.e. herrings and their relatives) can detect sounds up to 180 kHz (or even higher). It is suggested that this capability evolved so that these fishes can detect one of their major predators, echolocating dolphins. The mechanism for ultrasound detection remains obscure, though it is hypothesized that the highly derived utricle of the inner ear in these species is involved.

Animal Communication↗