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PubMed2003

Bilateral amplification for the elderly: are two aids better than one?

This paper reviews the advantages and disadvantages of bilateral amplification as opposed to unilateral hearing use for older persons with bilateral symmetric hearing loss. Binaural advantages, such as improved localization and speech recognition in noise, are presented as they pertain to the older population. In addition, contraindications, such as binaural interference, increased costs, cosmetic concerns, decreased manipulation skills, and additional hearing aid management issues, are discussed. A case study is provided in which unilateral hearing aid fitting was more beneficial to a patient than two hearing aids. It is concluded that bilateral amplification should be attempted for all elderly patients with symmetric hearing loss, unless a contraindication is suspected.

Aged↗

PubMed2005

Low-level integration of auditory and visual motion signals requires spatial co-localisation.

It is well known that the detection thresholds for stationary auditory and visual signals are lower if the signals are presented bimodally rather than unimodally, provided the signals coincide in time and space. Recent work on auditory-visual motion detection suggests that the facilitation seen for stationary signals is not seen for motion signals. We investigate the conditions under which motion perception also benefits from the integration of auditory and visual signals. We show that the integration of cross-modal local motion signals that are matched in position and speed is consistent with thresholds predicted by a neural summation model. If the signals are presented in different hemi-fields, move in different directions, or both, then behavioural thresholds are predicted by a probability-summation model. We conclude that cross-modal signals have to be co-localised and co-incident for effective motion integration. We also argue that facilitation is only seen if the signals contain all localisation cues that would be produced by physical objects.

Acoustic Stimulation↗

PubMed2005

Representational momentum in spatial hearing does not depend on eye movements.

The perceived final position of a moving object usually seems to be displaced in the direction of motion. This displacement effect, termed representational momentum, has been reported for both visual and acoustic targets. This study investigated whether representational momentum in the auditory modality depends on oculomotor behavior during target presentation. In a dark anechoic environment, subjects localized the final position of a horizontally moving acoustic target (continuous noise) by using a hand pointer. Subjects were instructed to pursue the acoustic target with their eyes, to maintain central gaze direction, or to fixate a central visual fixation point. Forward displacements of the perceived final target position occurred irrespective of the eye-movement condition. This result is not consistent with previous findings in the visual modality indicating a reduction of forward displacement for continuously moving targets with fixation. It is suggested that factors other than oculomotor behavior are the source of representational momentum in spatial hearing.

Acoustic Stimulation↗

PubMed2001

Multichannel auditory search: toward understanding control processes in polychotic auditory listening.

Two experiments are presented that serve as a framework for exploring auditory information processing. The framework is referred to as polychotic listening or auditory search, and it requires a listener to scan multiple simultaneous auditory streams for the appearance of a target word (the name of a letter such as A or M). Participants' ability to scan between two and six simultaneous auditory streams of letter and digit names for the name of a target letter was examined using six loudspeakers. The main independent variable was auditory load, or the number of active audio streams on a given trial. The primary dependent variables were target localization accuracy and reaction time. Results showed that as load increased, performance decreased. The performance decrease was evident in reaction time, accuracy, and sensitivity measures. The second study required participants to practice the same task for 10 sessions, for a total of 1800 trials. Results indicated that even with extensive practice, performance was still affected by auditory load. The present results are compared with findings in the visual search literature. The implications for the use of multiple auditory displays are discussed. Potential applications include cockpit and automobile warning displays, virtual reality systems, and training systems.

Adult↗

PubMed2001

Effects of hearing protectors on auditory localization in azimuth and elevation.

An experiment was conducted to determine the effects of two types of hearing protectors on auditory localization performance. Six listeners localized a 750-ms broadband noise from loudspeakers ranging in azimuth from -180 degrees to +180 degrees and in elevation from -75 degrees to +90 degrees. Independent variables included the type of hearing protector and the elevation of the source. Dependent measures included azimuth error, elevation error, and the percentage of trials resulting in a front-back confusion. Performance on each of the dependent measures was found to be mediated by one or more of the independent variables. Actual or potential applications include the generation of improved design guidelines for hearing protectors and workplace alarms.

Adolescent↗

PubMed1999

Predictability of the cue-target relation and the time-course of auditory inhibition of return.

The possibility that the time-course of auditory inhibition of return (IOR) might depend on the temporal or spatial predictability of the cue-target relation was investigated. In all the experiments, a location cue was followed by a target that was to be localized. An inhibitory effect became apparent at a longer stimulus onset asynchrony (SOA) when either the temporal or the spatial relation was predictable, rather than when either was unpredictable. A facilitative effect was apparent at a 100-msec SOA, irrespective of the predictability of the cue-target relation. These results establish that the time-course of the inhibitory component of location-based auditory IOR depends on the predictability of the temporal and spatial relations of cue and target. The theoretical implications of these results are considered, and a dual-process model of auditory selective attention is offered.

Adult↗

PubMed2003

Visual localization ability influences cross-modal bias.

The ability of a visual signal to influence the localization of an auditory target (i.e., "cross-modal bias") was examined as a function of the spatial disparity between the two stimuli and their absolute locations in space. Three experimental issues were examined: (a) the effect of a spatially disparate visual stimulus on auditory localization judgments; (b) how the ability to localize visual, auditory, and spatially aligned multisensory (visual-auditory) targets is related to cross-modal bias, and (c) the relationship between the magnitude of cross-modal bias and the perception that the two stimuli are spatially "unified" (i.e., originate from the same location). Whereas variability in localization of auditory targets was large and fairly uniform for all tested locations, variability in localizing visual or spatially aligned multisensory targets was much smaller, and increased with increasing distance from the midline. This trend proved to be strongly correlated with biasing effectiveness, for although visual-auditory bias was unexpectedly large in all conditions tested, it decreased progressively (as localization variability increased) with increasing distance from the midline. Thus, central visual stimuli had a substantially greater biasing effect on auditory target localization than did more peripheral visual stimuli. It was also apparent that cross-modal bias decreased as the degree of visual-auditory disparity increased. Consequently, the greatest visual-auditory biases were obtained with small disparities at central locations. In all cases, the magnitude of these biases covaried with judgments of spatial unity. The results suggest that functional properties of the visual system play the predominant role in determining these visual-auditory interactions and that cross-modal biases can be substantially greater than previously noted.

Adult↗

PubMed2003

Differential characteristics of the middle latency auditory evoked magnetic responses to interstimulus intervals.

OBJECTIVE: The human middle latency auditory evoked magnetic fields were recorded with different interstimulus intervals (ISI) to investigate the differential natures of P30m and the P50m, including whether the P50m source was spatially different or not from the P30m source. METHODS: Twenty right-handed healthy subjects participated in the experiment. Auditory magnetic responses were recorded in the 0.5 s ISI (ISI were between 0.4 and 0.6 s) and the 1.5 s ISI conditions (ISI were between 1 and 2 s). Tone bursts were presented to the right ears 880 times consecutively for each condition. The P30m and the P50m responses were investigated, and the dipole source localization was performed. RESULTS: The P50m latency was significantly prolonged, while the P30m latency did not vary in the shorter ISI. Both P50m and P30m amplitudes were significantly reduced in the shorter ISI. The P50m was located significantly more anteriorly than P30m. CONCLUSIONS: These results suggest the existence of differential characteristic and spatially different magnetic responses in the middle latency range. SIGNIFICANCE: This study has revealed one aspect of the different natures between P30m and P50m, and may provide a key for auditory perceptional processes in humans.

Acoustic Stimulation↗

PubMed1982

Hearing and language development in high risk and normal infants.

In the present study a group of 147 infants who are at risk for a loss are contrasted with 49 normal infants on an audiological screening battery, which is used to assess auditory and language variables. A descriptive comparison between expected and actual performance levels was made for both groups in regards to their respective receptive and expressive language, auditory localization, and speech detection threshold scores. In general the normal infants were found to perform at or above the expected performance level, whereas the high risk infants seemed to perform at or slightly below expectation. The interrelationships of these language and auditory variables along with age and birth weight were also calculated separately for each group. The direction and significance of these intercorrelations were the same for both groups with the exception of the birth weight correlations. These findings and their implications are discussed.

Attention↗

PubMed1981

Predictive value of early testing of auditory localization for language development.

This pilot study attempted to determine whether atypical localization to voice during the first year of life could be predictive of later delayed language development. 22 children who had been tested at six to nine months of age and found to have normal hearing were retrospectively divided into "atypical' and 'normal' groups. They were then evaluated for language development at four years of age. The atypical group had significantly lower scores on two of the four measures of language competence, but the results must be interpreted with caution because of the small number of children in the study.

Auditory Perception↗

PubMed2004

[A mismatch negativity elicited with stationary and moving auditory images of different azimuth positions].

Characteristics of mismatch negativity elicited by dichotic stimulation were examined using deviant stimuli simulating movement of fused auditory images towards the standard stimuli or in the reverse direction. The effect of stationary deviants localized at 90 degrees in respect to standards was also measured. The standard stimuli were localized near either of ears or along the head midline. The spatial locations were produced by introducing interaural time differences into the click trains. All deviant stimuli evoked the mismatch negativity. The deviants moving from standards seem to evoke the lowest mismatch negativity with the longest latency at all azimuthal locations of standard stimuli. Besides, the deviant shift from standards proved to be the only direction at which the characteristics of mismatch negativity depended upon the standard's azimuth. It is seems that the discrimination of interaural time delay is essentially dependent on the pattern of interaural delay changes at the moment when the deviant occurs.

Acoustic Stimulation↗

PubMed1992

Function-based modeling of binaural processing: interaural phase.

The intent of function-based modeling is to predict from theoretical considerations the input/output characteristics of a neuron if it were to perform a specific signal processing task within a sensory system. In this study, the sensory task is localization within the horizontal plane of a sustained low-frequency tone using interaural phase cues alone. The stimulus is assumed to be represented by primary-like discharge patterns from each ear. These patterns serve as the input to a system whose task is to extract the information needed to determine azimuthal angle. The optimal system resembles the classic Jeffress model, but differs from it in important details. In particular, the Jeffress model is shown to be a sub-optimal approximation in that it ignores the characteristic frequency of the inputs. The physical realization of either model by a structure resembling currently known MSO anatomy and innervation is discussed.

Acoustic Stimulation↗

PubMed1987

Auditory localization in the vertical plane: accuracy and constraint on bodily movement.

In two preliminary experiments, listeners were instructed to limit increasingly the movement of their heads and/or bodies while attempting to localize narrow bands of noise centered on 2.3 or 8.3 kHz. With increasing constraint on movement, the high-frequency band was incorrectly perceived as elevated above the horizon. The low-frequency band, when actually elevated above the horizon, was not so regularly perceived incorrectly as being below the horizon, a finding inconsistent with a previous report. A third experiment, which more closely replicated the task conditions and strategies of the previous study, did tend to reveal the anomalous low-frequency error. The error is explicable as a default response to which listeners whose sensitivity to the vertical dimension, in general, appears imperfect are prone. From various reports, it emerges that about 25% of presumed normally hearing people exhibit this insensitivity.

Auditory Perception↗

PubMed2003

Neural activity associated with binaural processes for the perceptual segregation of pitch.

OBJECTIVE: We measured late cortical potentials in a psychophysical procedure for binaural unmasking of a dichotically-embedded pitch. METHODS: Late-latency auditory evoked potentials were measured from 128 recording channels in 13 healthy subjects. Control stimuli consisted of 500 ms segments of broadband acoustic noise presented identically to both ears via earphones, evoking a perception of noise localized in the centre of the head. Dichotic pitch stimuli were created by introducing a dichotic delay to a narrow frequency region of the same noise segments, and resulted in a perception of both the centrally-located noise and a right-lateralized pitch. RESULTS: Both stimuli evoked late auditory event-related potentials (ERPs) characterized by a P1-N1-P2 complex of waves between 60 and 180 ms after stimulus onset. ERPs associated with the control and dichotic pitch stimuli showed no amplitude differences for the P1 and N1 waves. ERPs to dichotic pitch stimuli became significantly more negative beginning at a latency around 150 ms, an effect that was maximal between 210 and 280 ms. Topographic mapping showed that this late negativity was lateralized to the left hemisphere. CONCLUSIONS: The late negative wave elicited by the dichotic pitch stimulus reflects neural processing that is dependent upon binaural fusion within the auditory system. SIGNIFICANCE: The dichotic pitch paradigm may provide a useful tool for the electrophysiological assessment and study of the temporal processing capabilities of the auditory system. This paradigm may also be useful for the study of binaural mechanisms for the perceptual segregation of concurrent sound sources.

Adult↗

PubMed2004

Neuroplasticity after unilateral visual cortex damage in the newborn cat.

Anatomical, electrophysiological, and behavioral studies implicate extrastriate cortex as a major contributor to the sparing of visually guided behaviors following lesions of primary visual cortex incurred early in life. Here we report considerable sparing of the ability to detect and localize stimuli in the hemifield contralateral to unilateral early lesions of all contiguous visually-responsive primary and extrastriate cortical regions (occipital, visuoparietal, and visuotemporal cortices). In the adult cat this same lesion induces a dense blindness and cats are unable to orient to any visual stimulus introduced into the contralesional hemifield. In the absence of cortical circuits, the neural sparing identified following the neonatal lesion is based on the superior colliculus and it occurs despite massive retrograde transynaptic degeneration of large numbers of retinal ganglion cells.

Animals↗

PubMed1991

Developmental perspectives on the localization and detection of auditory signals.

Responsiveness of 1-, 3-, and 5-year-old children and adults to octave-band noises at .4 and 10 kHz was assessed with a go/no-go version of visual reinforcement audiometry (VRA) (Moore, Thompson, & Thompson, 1975) and a two-alternative, forced-choice version (Suzuki & Ogiba, 1961; Trehub, Schneider, & Endman, 1980). Infants performed better on the two-alternative, forced-choice version in quiet and in noisy backgrounds, and adults performed better on the two-alternative, forced-choice version in quiet but not in noisy backgrounds. Performance on the two tasks was essentially equivalent for 3- and 5-year-old children. Superior performance on two-alternative VRA over go/no-go may be due to lesser cognitive demands in the case of infants and to the engagement of superior decision strategies in the case of adults.

Adolescent↗

PubMed2003

Visual reinforcement audiometry using digital video disc and conventional reinforcers.

Visual reinforcement audiometry (VRA) is a test procedure routinely used to evaluate hearing in infants and young children (6 months to 2 years). Most research and current clinical practice uses flashing lights and/or animated toys to provide reinforcement to a child during VRA. New technology capable of generating a moving video image is now available for providing visual reinforcement to infants during VRA testing. It is reasonable to expect that video images, with presumed greater novelty and complexity, would be more interesting and rewarding to children than conventional, animated mechanical toy reinforcers. On the other hand, in today's society, children are frequently exposed to video images in the home and elsewhere. Therefore, three-dimensional animated toys may present with greater novelty than video images. The purpose of this study was to compare auditory localization behavior, as defined by the number of head turn responses until habituation, during VRA with 2-year-old children using two types of reinforcers: (a) moving images generated by a digital video disc player/monitor and (b) a conventional, animated mechanical toy. Twenty children were selected randomly from a total group of 40 and tested using conventional reinforcement. The remaining 20 children were tested using video reinforcement. The average number of head turn responses prior to habituation was approximately 15 for the video-reinforced group and approximately 11 for the conventional toy-reinforced group, suggesting that during VRA a video image may be more reinforcing than a conventional animated toy.

Audiometry↗

PubMed2006

Binaural segregation in multisource reverberant environments.

In a natural environment, speech signals are degraded by both reverberation and concurrent noise sources. While human listening is robust under these conditions using only two ears, current two-microphone algorithms perform poorly. The psychological process of figure-ground segregation suggests that the target signal is perceived as a foreground while the remaining stimuli are perceived as a background. Accordingly, the goal is to estimate an ideal time-frequency (T-F) binary mask, which selects the target if it is stronger than the interference in a local T-F unit. In this paper, a binaural segregation system that extracts the reverberant target signal from multisource reverberant mixtures by utilizing only the location information of target source is proposed. The proposed system combines target cancellation through adaptive filtering and a binary decision rule to estimate the ideal T-F binary mask. The main observation in this work is that the target attenuation in a T-F unit resulting from adaptive filtering is correlated with the relative strength of target to mixture. A comprehensive evaluation shows that the proposed system results in large SNR gains. In addition, comparisons using SNR as well as automatic speech recognition measures show that this system outperforms standard two-microphone beamforming approaches and a recent binaural processor.

Environment↗