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PubMed2004

A detection-theoretic model of echo inhibition.

A detection-theoretic analysis of the auditory localization of dual-impulse stimuli is described, and a model for the processing of spatial cues in the echo pulse is developed. Although for over 50 years "echo suppression" has been the topic of intense theoretical and empirical study within the hearing sciences, only a rudimentary understanding of its mechanisms has emerged. In this article, psychometric functions and results from matching studies are used in developing a model that specifies the perceived position of the echo pulse as a normal deviate, with an expectation that is a logistic function of the echo delay and a variance that depends on interaural time difference. Loss of information in the echo event is quantified as a decline in the efficiency with which the binaural system receives information from the lag impulse.

Attention↗
PubMed1992

Inherent problems of attempts to apply sonar and vibrotactile sensory aid technology to the perceptual needs of the blind.

A program of research dealing with two types of sensory aids for the blind--sonar and vibrotactile--is described. Rather than immediately assessing the aids in the mobility context, which has customarily been the case, the aids' capabilities are considered in terms of the major functions of vision, that is, the exteroceptive perception of objects, surfaces, and events of the environment, and the proprioceptive perception of the self, especially the self in relation to the environment. Although sonar aids function very well for localizing objects and for providing acoustic flow specifying self-movement, they do not provide high acuity pattern and shape information due to the long wavelength of ultrasound relative to light. This limitation is considered specifically with respect to the visual accomplishment of recovery of three-dimensional structure/motion from dynamic two-dimensional images. Vibrotactile sensory aids using optical imaging can deliver detailed pattern information to the skin and thus permit assessment of the extent to which a nonvisual system can mediate the recovery of structure problem. However, in even moderately cluttered or complicated environments the skin proves unable to resolve the amount of stimulation it receives vibrotactually. The limitations of sonar and vibrotactile sensory aids are discussed with respect to future sensory substitution efforts as well as their implications for understanding differences and similarities among the senses.

Blindness↗
PubMed2003

Bayesian integration of visual and auditory signals for spatial localization.

Human observers localize events in the world by using sensory signals from multiple modalities. We evaluated two theories of spatial localization that predict how visual and auditory information are weighted when these signals specify different locations in space. According to one theory (visual capture), the signal that is typically most reliable dominates in a winner-take-all competition, whereas the other theory (maximum-likelihood estimation) proposes that perceptual judgments are based on a weighted average of the sensory signals in proportion to each signal's relative reliability. Our results indicate that both theories are partially correct, in that relative signal reliability significantly altered judgments of spatial location, but these judgments were also characterized by an overall bias to rely on visual over auditory information. These results have important implications for the development of cue integration and for neural plasticity in the adult brain that enables humans to optimally integrate multimodal information.

Bayes Theorem↗
PubMed2001

The spectrally dependent monotic component in the decreasing-loudness aftereffect: implications for dynamic auditory localization.

Listeners exposed to a tone increasing in intensity report an aftereffect of decreasing loudness in a steady tone heard afterward. In the present study, the spectral dependence of the monotic decreasing-loudness aftereffect (adapting and testing 1 ear) was compared with (a) the spectral dependence of the interotic decreasing-loudness aftereffect (adapting 1 ear and testing the other ear) and (b) a non-adaptation control condition. The purpose was to test the hypothesis that the decreasing-loudness aftereffect may concern the sensory processing associated with dynamic localization. The hypothesis is based on two premises: (a) dynamic localization requires monaural sensory processing, and (b) sensory processing is reflected in spectral selectivity. Hence, the hypothesis would be supported if the monotic aftereffect were more spectrally dependent and stronger than the interotic aftereffect; A. H. Reinhardt-Rutland (1998) showed that the hypothesis is supported with regard to the related increasing-loudness aftereffect. Two listeners were exposed to a 1-kHz adapting stimulus. From responses of "growing softer" or "growing louder" to test stimuli changing in intensity, nulls were calculated; test carrier frequencies ranged from 0.5 kHz to 2 kHz. Confirming the hypothesis, the monotic aftereffect peaked at around the 1-kHz test carrier frequency. In contrast, the interotic aftereffect showed little evidence of spectrally dependent peaking. Except when test and adaptation carrier frequencies differed markedly, the interotic aftereffect was smaller than the monotic aftereffect.

Female↗
PubMed1997

Evidence for primary auditory cortex involvement in the echo suppression precedence effect: a 3CLT study.

An echo lagging shortly after a source and arising from another direction perceptually blends with the source, and the location of the fused 'source-echo' is dominated by the source location (the Precedence Effect). The neural substrates underlying the echo localization suppression are ambiguous. We recently suggested an auditory evoked potentials correlate of binaural echo lateralization suppression. A significant and specific reduction in binaural peak amplitude and area of the echo-evoked middle-latency component Pa was observed. The binaural echo-Pa suppression depended on echo lag and correlated with the psychophysical echo lateralization suppression. In this study, the echo-Pa generators were analyzed with 3CLT spatio-temporal analysis, in order to suggest the neural substrates involved in echo lateralization suppression. 3CLT enables reliable identification of components, based on rigid geometrical properties. The results suggest that the Pa1 subcomponent of Pa, associated with primary auditory cortex activity, fully accounts for the echo-Pa suppression. This physiological indication for primary auditory cortex involvement in the precedence effect is the first in humans.

Acoustic Stimulation↗
PubMed2006

Benefits of bilateral cochlear implants and/or hearing aids in children.

This study evaluated functional benefits from bilateral stimulation in 20 children ages 4-14, 10 use two CIs and 10 use one CI and one HA. Localization acuity was measured with the minimum audible angle (MAA). Speech intelligibility was measured in quiet, and in the presence of 2-talker competing speech using the CRISP forced-choice test. Results show that both groups perform similarly when speech reception thresholds are evaluated. However, there appears to be benefit (improved MAA and speech thresholds) from wearing two devices compared with a single device that is significantly greater in the group with two CI than in the bimodal group. Individual variability also suggests that some children perform similarly to normal-hearing children, while others clearly do not. Future advances in binaural fitting strategies and improved speech processing schemes that maximize binaural sensitivity will no doubt contribute to increasing the binaurally-driven advantages in persons with bilateral CIs.

Adolescent↗
PubMed1986

Extension of a binaural cross-correlation model by contralateral inhibition. I. Simulation of lateralization for stationary signals.

Running interaural cross correlation is a basic assumption to model the performance of the binaural auditory system. Although this concept is particularly suited to simulate psychoacoustic localization phenomena, there exist some localization effects which cannot be explained by pure cross correlation. In this paper a model of interaural cross correlation is extended by a "contralateral-inhibition mechanism" and by "monaural detectors" in order to simulate a wide range of psychoacoustic lateralization data. The extended model explains lateralization of pure tones with interaural time differences as well as with interaural level differences. Multiple images are predicted for tones with characteristic combinations of interaural signal parameters and for noise signals with different degrees of interaural cross correlation. The model is also capable of simulating dynamic lateralization phenomena, such as the "law of the first wave front" which is dealt with in a companion paper [Lindemann, J. Acoust. Soc. Am. 80, 1623-1630 (1986)]. The present paper is restricted to a comparison of the model predictions for stationary signals with the results of dichotic listening experiments.

Auditory Perception↗
PubMed2007

[On the relation between binaural difference potentials and directional hearing].

BACKGROUND: Central auditory processing disorders (CAPD) are associated with reduced discriminatory abilities of the auditory system. One of these abilities is directional hearing, which is based on the evaluation of interaural signal differences. Since these differences affect also the binaural difference potentials (BDP), these derived evoked potentials could be suitable for the objective detection of disabilities in acoustic localization. METHOD: Auditory brainstem responses (ABR) evoked by monaural and binaural stimulation were recorded in 32 adult normal-hearing volunteers at stimulus levels between 10 and 80 dB nHL and the BDP were derived. Additionally, a test of directional hearing was performed and evaluated. RESULTS: BDP are detectable at all stimulus levels without difficulties, with acceptable examination times and with satisfactory reliability in a routine clinical environment. The electrodes can be positioned at the mastoid (A1 and A2) and vertex (Cz) as for conventional ABR recording. Normal ranges are given for latency and amplitude as well as for their lateral differences. CONCLUSION: The spectrum in directional hearing ability as covered by normal-hearing subjects is not mirrored in the parameters of their BDP. Nevertheless, it cannot be ruled out that a real impairment of directional hearing goes along with significantly altered BDP.

Adult↗
PubMed2005

Rotation or translation of auditory space in neglect? A case study of chronic right-sided neglect.

Egocentric models of neglect explain the lateralised omission of stimuli in neglect patients by an ipsilesional shift of a subjective reference frame. However, they differ in the direction of shift (rotation around the midsagittal plane versus translation in front/back space). We tested this hypothesis in a patient (AJ) with persistent right-sided neglect following a left temporo-parieto-occipital and hypoxic lesion and in six age-matched healthy subjects. AJ showed visual neglect in line bisection, size matching, reading and visual search. Auditory localization was tested by using two different psychophysical techniques based on binaurally simulated stimuli for the horizontal plane in front and back space. Eye position was continuously monitored during stimulus presentation in all subjects. AJ revealed a significant ipsilesional, leftward shift of his auditory subjective median plane (ASMP) in front space (mean: -22.6 degrees), and a rightward shift of the ASMP in back space (+14.5 degrees). This pattern of results was replicated with a different psychophysical technique in a retest 10 months later. The rotational shift of AJ's ASMP contrasted with normal performance in the healthy subjects. Monaural hearing deficits can not account for these differential findings as all subjects (including AJ) performed normally. In conclusion, a rotation of the egocentric spatial reference frame may occur in the auditory modality for right-sided neglect.

Acoustic Stimulation↗
PubMed1985

Accuracy, latency, and listener-search behavior in localization in the horizontal and vertical planes.

Thirty-six listeners localized continuous filtered noise bursts centered on 2.3 or 8.3 kHz under normal listening conditions or while wearing earmuffs. The noise bursts were from any one of 20 loudspeakers, 18 degrees apart, visible to the listeners, and arranged in the horizontal and vertical planes. Listeners were free to move, while remaining seated, throughout all trials. The noise bursts were terminated by the listeners. Measures of accuracy and latency showed that earmuff listening had a significant effect whereas, overall, signal frequency had no significant effect. There was, however, an apparent downward shift of the 2.3-kHz signals presented above the midline in the vertical plane. Analysis of video records of listeners' behavior revealed a strong tendency for initial orientation by head or eye movement to correlate with final response, even when both were inaccurate. The paradigm adopted in this latter aspect of the study illustrates an "ecological" approach to the study of auditory phenomena.

Acoustic Stimulation↗
PubMed1993

Forward masking properties of neurons in the dorsal cochlear nucleus: possible role in the process of echo suppression.

The majority of single unit studies in the auditory system have been carried out using stimuli whose temporal and spectral contexts are held constant. Relatively little attention has been given to the influence of context on unit response properties. Indeed, auditory nerve fiber responses are known to be context-dependent due to the property of forward masking, a phenomenon by which the response to one sound results in a reduction in the response to a subsequent sound. Forward masking might be expected to be even more influential at central levels of the auditory pathway where the responses are reshaped by additional synaptic interactions. The purpose of the present study was to characterize the forward masking properties of neurons in the dorsal cochlear nucleus (DCN). A tool was developed for measuring the response to a probe tone as a function of delay following a previous tone-burst. The frequency of the probe was held constant at the unit's characteristic frequency while the frequency of the leading tone (masker) was varied. These measures provided a description of neural masking effects in different temporal and spectral contexts. The data yielded two patterns of suppression. In the first pattern (Type A), the suppression of the probe response became evident immediately following offset of the masker; the suppression bandwidth showed a gradual narrowing as the delay between masker and probe was increased. In the second class (Type B), the suppression of the probe response did not become evident until well after offset of the masker; this pattern appeared more circumscribed in that the suppression bandwidth gradually increased as a function of delay up to a maximum then decreased with further increases in delay. The results imply that mechanisms intrinsic to the DCN contribute to further modification and reshaping of the spectral and temporal context of masking effects beyond those seen in the auditory nerve. It is hypothesized that such properties may be specialized for suppressing the response to echoes thus facilitating communication and localization of sound in enclosed spaces.

Acoustic Stimulation↗
PubMedDate not supplied

Source levels and the estimated active space of bottlenose dolphin (Tursiops truncatus) whistles in the Moray Firth, Scotland.

This study measured SPLs of whistles of wild bottlenose dolphins (Tursiops truncatus) in the Moray Firth, Scotland, and estimated their active space, i.e. the distance at which another dolphin can perceive the whistle of a conspecific. Whistling dolphins were localized with a dispersed hydrophone array by comparing differences in the times of arrival of a whistle at different hydrophones. The mean source level for whistles was 158 +/- 0.6 dB re. 1 microPa. The maximum was 169 dB re. 1 microPa. The active space of these whistles was calculated taking into account transmission loss, ambient noise, the critical ratios and the auditory sensitivity of this species. The estimated radius of the active space of unmodulated whistles between 3.5 kHz and 10 kHz produced at maximum source level ranged from 20 km to 25 km in a habitat of 10 m depth and at sea state 0. At sea state 4 it ranged from 14 km to 22 km. For whistles of 12 kHz it dropped to 1.5-4 km. The results suggest that whistles can be used to maintain group cohesion over large distances but also that dolphins that researchers consider to belong to separate groups might be in acoustic contact.

Acoustic Stimulation↗
PubMed2005

The effect of auditory experience on speech perception, localization, and functional performance of children who use a cochlear implant and a hearing aid in opposite ears.

This study was aimed at determining the effect of auditory experience on binaural benefits from using a cochlear implant and a hearing aid in opposite ears. Eighteen children were evaluated using tests of speech perception, horizontal localization, and functional performance when they used either a cochlear implant alone (CI) or a cochlear implant with a hearing aid (CIHA). Eight were experienced CIHA users, whereas ten had not worn a hearing aid in the non-implanted ear for up to eight years prior to participation. All children were fitted with a hearing aid in the non-implanted ear using the NAL-RP prescription, and the hearing aids were fine-tuned individually using a paired-comparisons procedure and a loudness balancing test. Evaluation results indicated that performance for all measures was significantly better with CIHA than with CI for both groups of children. We conclude that children who receive a unilateral cochlear implant should be encouraged to wear a hearing aid in the opposite ear where there is usable residual hearing.

Acoustic Stimulation↗
PubMed1998

Adapting to supernormal auditory localization cues. I. Bias and resolution.

Head-related transfer functions (HRTFs) were used to create spatialized stimuli for presentation through earphones. Subjects performed forced-choice, identification tests during which allowed response directions were indicated visually. In each experimental session, subjects were first presented with auditory stimuli in which the stimulus HRTFs corresponded to the allowed response directions. The correspondence between the HRTFs used to generate the stimuli and the directions was then changed so that response directions no longer corresponded to the HRTFs in the natural way. Feedback was used to train subjects as to which spatial cues corresponded to which of the allowed responses. Finally, the normal correspondence between direction and HRTFs was reinstated. This basic experimental paradigm was used to explore the effects of the type of feedback provided, the complexity of the stimulated acoustic scene, the number of allowed response positions, and the magnitude of the HRTF transformation subjects had to learn. Data showed that (1) although subjects may not adapt completely to a new relationship between physical stimuli and direction, response bias decreases substantially with training, and (2) the ability to resolve different HRTFs depends both on the stimuli presented and on the state of adaptation of the subject.

Adolescent↗
PubMed1999

Early visual experience shapes the representation of auditory space in the forebrain gaze fields of the barn owl.

Auditory spatial information is processed in parallel forebrain and midbrain pathways. Sensory experience early in life has been shown to exert a powerful influence on the representation of auditory space in the midbrain space-processing pathway. The goal of this study was to determine whether early experience also shapes the representation of auditory space in the forebrain. Owls were raised wearing prismatic spectacles that shifted the visual field in the horizontal plane. This manipulation altered the relationship between interaural time differences (ITDs), the principal cue used for azimuthal localization, and locations of auditory stimuli in the visual field. Extracellular recordings were used to characterize ITD tuning in the auditory archistriatum (AAr), a subdivision of the forebrain gaze fields, in normal and prism-reared owls. Prism rearing altered the representation of ITD in the AAr. In prism-reared owls, unit tuning for ITD was shifted in the adaptive direction, according to the direction of the optical displacement imposed by the spectacles. Changes in ITD tuning involved the acquisition of unit responses to adaptive ITD values and, to a lesser extent, the elimination of responses to nonadaptive (previously normal) ITD values. Shifts in ITD tuning in the AAr were similar to shifts in ITD tuning observed in the optic tectum of the same owls. This experience-based adjustment of binaural tuning in the AAr helps to maintain mutual registry between the forebrain and midbrain representations of auditory space and may help to ensure consistent behavioral responses to auditory stimuli.

Adaptation, Physiological↗
PubMed1999

Midbrain combinatorial code for temporal and spectral information in concurrent acoustic signals.

All vocal species, including humans, often encounter simultaneous (concurrent) vocal signals from conspecifics. To segregate concurrent signals, the auditory system must extract information regarding the individual signals from their summed waveforms. During the breeding season, nesting male midshipman fish (Porichthys notatus) congregate in localized regions of the intertidal zone and produce long-duration (>1 min), multi-harmonic signals ("hums") during courtship of females. The hums of neighboring males often overlap, resulting in acoustic beats with amplitude and phase modulations at the difference frequencies (dFs) between their fundamental frequencies (F0s) and harmonic components. Behavioral studies also show that midshipman can localize a single hum-like tone when presented with a choice between two concurrent tones that originate from separate speakers. A previous study of the neural mechanisms underlying the segregation of concurrent signals demonstrated that midbrain neurons temporally encode a beat's dF through spike synchronization; however, spectral information about at least one of the beat's components is also required for signal segregation. Here we examine the encoding of spectral differences in beat signals by midbrain neurons. The results show that, although the spike rate responses of many neurons are sensitive to the spectral composition of a beat, virtually all midbrain units can encode information about differences in the spectral composition of beat stimuli via their interspike intervals (ISIs) with an equal distribution of ISI spectral sensitivity across the behaviorally relevant dFs. Together, temporal encoding in the midbrain of dF information through spike synchronization and of spectral information through ISI could permit the segregation of concurrent vocal signals.

Acoustic Stimulation↗
PubMedDate not supplied

Crossmodal integration for perception and action.

The integration of information from different sensory modalities has many advantages for human observers, including increase of salience, resolution of perceptual ambiguities, and unified perception of objects and surroundings. Several behavioral, electrophysiological and neuroimaging data collected in various tasks, including localization and detection of spatial events, crossmodal perception of object properties and scene analysis are reviewed here. All the results highlight the multiple faces of crossmodal interactions and provide converging evidence that the brain takes advantages of spatial and temporal coincidence between spatial events in the crossmodal binding of spatial features gathered through different modalities. Furthermore, the elaboration of a multimodal percept appears to be based on an adaptive combination of the contribution of each modality, according to the intrinsic reliability of sensory cue, which itself depends on the task at hand and the kind of perceptual cues involved in sensory processing. Computational models based on bayesian sensory estimation provide valuable explanations of the way perceptual system could perform such crossmodal integration. Recent anatomical evidence suggest that crossmodal interactions affect early stages of sensory processing, and could be mediated through a dynamic recurrent network involving backprojections from multimodal areas as well as lateral connections that can modulate the activity of primary sensory cortices, though future behavioral and neurophysiological studies should allow a better understanding of the underlying mechanisms.

Animals↗
PubMed1981

Infants' detection of speech in noise.

Localization responses to a speech phrase masked by white noise were obtained from infants 6, 12, 18, and 24 months of age and from adults. The masking noise was presented continuously from two loudspeakers located 45 degrees to each side of the infant. During a trial the speech phrase was presented through one of the loudspeakers. A head turn to the signal (correct response) was rewarded by activating an animated toy on top of the speaker. The intensity of the signal was varied over trials (method of constant stimuli) to determine thresholds (defined as the intensity corresponding to 65% correct head turns) at each of two levels of masking noise, 42 and 60 dBC. Thresholds for the speech signal were comparable across all infant groups for both levels of masking noise. Increasing the masking noise from 42 to 60 dBC resulted in a threshold shift of comparable magnitude for infants and adults. However, adult thresholds were approximately 10-12 dB lower than those of infants at both masking levels.

Auditory Threshold↗