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At least 1,081 records · Page 60Linked to original sources
PubMed2001

Sound lateralization during passive whole-body rotation.

The effect of passive whole-body rotation about the earth-vertical axis on the lateralization of dichotic sound was investigated in human subjects. Pure-tone pulses (1 kHz; 0.1 s duration) with various interaural time differences were presented via headphones during brief, low-amplitude rotation (angular acceleration 400 degrees/s2; maximum velocity 90 degrees/s; maximum displacement 194 degrees ). Subjects made two-alternative forced-choice (left/right) judgements on the acoustic stimuli. The auditory median plane of the head was shifted opposite to the direction of rotation, indicating a shift of the intracranial auditory percept in the direction of rotation. The mean magnitude of the shift was 10.7 micros. This result demonstrates a slight, but significant, influence of rotation on sound lateralization, suggesting that vestibular information is taken into account by the brain for accurate localization of stationary sound sources during natural head and body motion.

Adult↗
PubMed1982

Binaural localization.

In this paper we review some issues which are relevant to the formation of special positions and extents of auditory events in the case of two normally functioning ears. Physical aspects under consideration are measurement and analysis of the transfer functions of the external ears. These transfer functions are responsible for encoding information about the spatial characteristics of sound fields into the ear input signals. The hearing system can decode this information by evaluating interaural and monaural cues of these signals. A rough outline of psychoacoustical effects and mechanisms involved in this evaluation is given and a conceptual model of binaural interaction is described.

Animals↗
PubMed1979

Auditory lateralization in monkeys: an examination of two cues serving directional hearing.

In assigning binaural ongoing time differences (phase) as the cue for localization of low frequencies, and binaural intensity differences as the cue for localization of high frequencies, the duplex theory has successfully accounted for human directional hearing of tones. Sensitivity of monkeys to these cues was examined in two experiments. The dependencies on frequency of interaural intensity difference thresholds (lateralization experiment I) and time difference thresholds (lateralization experiment II) were determined behaviorally on three monkeys (M. nemestrina). The range of frequencies was from 125 Hz to 8 kHz in experiment I and from 250 Hz to 2 kHz in experiment II. The results indicate that the duplex theory is applicable to monkeys. However, monkeys are less sensitive than man to both binaural cues. The shortest time disparity monkeys discriminate is 42 microseconds at 1.5 kHz and the smallest intensity difference is 3.5 dB at 500 Hz. Good agreement between the present findings and localization measurements [C. H. Brown et al., J. Acoust. Soc. Am. 63, 1484-1492 (1978)] suggests: (a) that monkeys utilize time disparity cues through higher frequencies than man; and (b) that inaccurate localization by monkeys at high frequencies reflects decreasing sensitivity to interaural intensity cues.

Acoustic Stimulation↗
PubMed2005

Early phase of spatial mismatch negativity is localized to a posterior "where" auditory pathway.

The auditory mismatch negativity (MMN) is an event-related potential that reflects early processing of changes in acoustic stimulus features. Although the MMN has been well characterized by previous work, the number, roles, and anatomical locations of its cortical generators remain unresolved. Here, we report that the MMN elicited by occasional deviations in sound location is comprised of two temporally and anatomically distinct phases: an early phase with a generator posterior to auditory cortex and contralateral to the deviant stimulus, and a later phase with generators that are more frontal and bilaterally symmetric. The posterior location of the early-phase generator suggests the engagement of neurons within a putative "where" pathway for processing spatial auditory information.

Acoustic Stimulation↗
PubMed1990

Minimum audible angle thresholds for sources varying in both elevation and azimuth.

Minimum audible angle (MAA) thresholds were obtained for four subjects in a two-alternative, forced-choice, three up/one down, adaptive paradigm as a function of the orientation of the array of sources. With sources distributed on the horizontal plane, the mean MAA threshold was 0.97 degrees. With the sources distributed on the vertical plane (array rotated 90 degrees), the mean MAA threshold was 3.65 degrees. Performance in both conditions was well in line with previous experiments of this type. Tests were also conducted with sources distributed on oblique planes. As the array was rotated from 10 degrees-60 degrees from the horizontal plane, relatively little change in the MAA threshold was observed; the mean MAA thresholds ranged from 0.78 degrees to 1.06 degrees. Only when the array was nearly vertical (80 degrees) was there any appreciable loss in spatial resolution; the MAA threshold had increased to 1.8 degrees. The relevance of these results to research on auditory localization under natural listening conditions, especially in the presence of head movements, is also discussed.

Adult↗
PubMed1995

Differences in localization ability in cases of right versus left unilateral simulated conductive hearing loss.

The purpose of this study was to determine whether localization errors were greater in cases of right ear unilateral simulated conductive loss, as compared to left ear simulated conductive loss of the same degree and configuration. Thirty adults were asked to localize a 3-kHz warbled pure tone with their left and right ears alternately occluded with an earplug. Significantly greater localization difficulty was found when the right ear was occluded. The average error was 58 degrees with the left ear plugged and 64 degrees when the right ear was occluded, which approximates the 65-degree average error that would have resulted from random guessing. This suggests that short-term conductive losses result in unusually poor localization ability, which is worse if the right ear is affected.

Adolescent↗
PubMed1991

Acceptability of binaural hearing aids: a cross-over study.

Using screening questionnaires we were able to detect individuals aged 50-65 years with hearing disability in a general practice population. Those who had better ear hearing levels of 30 dB or worse were invited to take place in a cross-over study comparing the acceptability of a monaural or binaural hearing-aid fitting. Fifty-five per cent ultimately opted for a binaural fitting and had greater hearing disability and worse mean hearing levels than those who opted for a monaural fitting. They made their choice for acoustical reasons, particularly on the basis of improved localization ability.

Audiometry↗
PubMed1992

The role of localization in visual reinforcement audiometry.

The response task employed in visual reinforcement audiometry (VRA) has been characterized both as a localization response and, alternatively, as a pure operant conditioning behavior independent of localization. This study examined the role of localization in VRA conditioning and threshold procedures by varying the localization information provided to normal infants. Results indicate (a) that the VRA response is not contingent on localization but (b) that performance may be significantly influenced by localization. The findings suggest that any variable that alters proper localization cues, including equipment arrangement or impaired auditory function, may degrade response performance.

Audiometry, Speech↗
PubMed2001

Effects of CIC hearing aids on auditory localization by listeners with normal hearing.

An experiment was conducted to determine the effects of completely-in-the-canal (CIC) hearing aids on auditory localization performance. Six normal-hearing 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 presence or absence of the hearing aid and the elevation of the source. Dependent measures included azimuth error, elevation error, and the percentage of trials resulting in a front-back confusion. The findings indicate a statistically significant decrement in localization acuity, both in azimuth and elevation, occasioned by the wearing of CIC hearing aids. However, the magnitude of this decrement was small compared to those typically caused by other ear-canal occlusions, such as earplugs, and would probably not engender mislocalization of real-world sounds.

Adult↗
PubMed2004

Localization dominance in the median-sagittal plane: effect of stimulus duration.

Localization dominance is an aspect of the precedence effect (PE) in which the leading source dominates the perceived location of a simulated echo (lagging source). It is known to be robust in the horizontal/azimuthal dimension, where binaural cues dominate localization. However, little is known about localization dominance in conditions that minimize binaural cues, and most models of precedence treat the phenomena as "belonging" to the binaural system. Here, localization dominance in the median-sagittal plane was studied where binaural cues are greatly reduced, and monaural spectral/level cues are thought to be the primary cues used for localization. Lead-lag pairs of noise bursts were presented from locations spaced in 15 degrees increments in the frontal, median-sagittal plane, with a 2-ms delay in their onsets, for source durations of 1, 10, 25, and 50-ms. Intermixed with these trials were single-speaker trials, in which lead and lag were summed and presented from one speaker. Listeners identified the speaker that was nearest to the perceived source location. With single-speaker stimuli, localization improves as signal duration is increased. Furthermore, evidence of elevation compression was found with a dependence on duration. With lead-lag pairs, localization dominance occurs in the median plane, and becomes more robust with increased signal duration. These results suggest that accurate localization of a co-located lead-lag pair is necessary for localization dominance to occur when the lag is spatially separated from the lead.

Acoustic Stimulation↗
PubMedDate not supplied

Directionality in the mechanical response to substrate vibration in a treehopper (Hemiptera: Membracidae: Umbonia crassicornis).

The use of substrate vibrations in communication and predator-prey interactions is widespread in arthropods. In many contexts, localization of the vibration source plays an important role. For small species on solid substrates, time and amplitude differences between receptors in different legs may be extremely small, and the mechanisms of vibration localization are unclear. Here we ask whether directional information is contained in the mechanical response of an insect's body to substrate vibration. Our study species was a membracid treehopper (Umbonia crassicornis) that communicates using bending waves in plant stems. We used a bending-wave simulator that allows precise control of the frequency, intensity and direction of the vibrational stimulus. With laser-Doppler vibrometry, we measured points on the substrate and on the insect's thorax and middle leg. Transfer functions showing the response of the body relative to the substrate revealed resonance at lower frequencies and attenuation at higher frequencies. There were two modes of vibration along the body's long axis, a translational and a rotational mode. Furthermore, the transfer functions measured on the body differed substantially depending on whether the stimulus originated in front of or behind the insect. Directional information is thus available in the mechanical response of the body of these insects to substrate vibration. These results suggest a vibration localization mechanism that could function at very small spatial scales.

Acoustic Stimulation↗
PubMed2006

The effect of multi-channel wide dynamic range compression, noise reduction, and the directional microphone on horizontal localization performance in hearing aid wearers.

This study examined the effect that signal processing strategies used in modern hearing aids, such as multi-channel WDRC, noise reduction, and directional microphones have on interaural difference cues and horizontal localization performance relative to linear, time-invariant amplification. Twelve participants were bilaterally fitted with BTE devices. Horizontal localization testing using a 360 degrees loudspeaker array and broadband pulsed pink noise was performed two weeks, and two months, post-fitting. The effect of noise reduction was measured with a constant noise present at 80 degrees azimuth. Data were analysed independently in the left/right and front/back dimension and showed that of the three signal processing strategies, directional microphones had the most significant effect on horizontal localization performance and over time. Specifically, a cardioid microphone could decrease front/back errors over time, whereas left/right errors increased when different microphones were fitted to left and right ears. Front/back confusions were generally prominent. Objective measurements of interaural differences on KEMAR explained significant shifts in left/right errors. In conclusion, there is scope for improving the sense of localization in hearing aid users.

Adult↗
PubMedDate not supplied

Hearing loss and treatment in young Down's syndrome children.

Twenty-four home-reared Down's syndrome children aged 9-32 months were assessed by trained audiologists on three separate occasions (summer, autumn and spring 1977-1978). Distraction test procedures were used; all failed to pass the screening test and 80-85% registered as having moderate to profound losses. Seventy-five per cent were categorized as having a conductive loss and some improvements were found over the test sessions as a result of surgical and decongestant treatment. Approximately 50% of the infants had been passed on similar screening procedures by the local health services. The results are discussed in relation to language development and service needs.

Child, Preschool↗
PubMed1981

Cerebellar interaction with the acoustic reflex.

The involvement of the cerebellar vermis in the acoustic reflex was analyzed in 12 cats, decerebrated or in pentobarbital anesthesia. Anatomical data suggested the existence of a connection of lobules VIII with the ventral cochlear nucleus. Single cell recording and evoked potential techniques demonstrated the existence of the acoustic projection to lobulus VIII. Electrical stimulation of this area changed the tension of the middle ear muscle and caused evoked potential responses in the caudal part of the ventral cochlear nucleus. Electrical stimulation of the motor nucleus of the facial nerve evoked a slow wave in the recording taken from the surrounding of the cochlear round window. A hypothesis is proposed which postulates the involvement of the acoustic reflex in space localization of acoustic stimuli and the action of cerebellar vermis in order to assure the stability and plasticity of the acoustic reflex arc.

Animals↗
PubMed2001

Neural models for auditory localization based on spectral cues.

In this paper we analyze several auditory localization neural models that are based on head related transfer functions (HRTFs). HRTFs represent the combined directional-spectral response of the pinnae head and torso. The role of HRTFs in such modeling has hitherto been underestimated despite substantial experimental evidence to its relevance in spatial hearing, especially in determining direction of high-frequency sound sources. In the first section we suggest a neural model that links the physiology of binaural processing to a neural network that extracts spectral ratios. These ratios correspond to HRTFs ratios and can provide auditory directional cues. Next, we compare several methods of matching HRTFs ratios using discriminative matching measure (DMM). We consider several solutions to the matching problem from a neural signal processing viewpoint. We compare correlation based approaches with DMM optimization approach and with a non-linear approach based on neural back-propagation algorithm. All three models can be implemented by neural networks. Finally, we include experimental results of simulations that are conducted using these methods. Experiments show that the back-propagation based neural network yields the best results in terms of DMM both for narrow-band and broad band excitation. The back-propagation neural network is also superior in matching noisy HRTF ratio vectors.

Animals↗
PubMed2004

Auditory neuroscience: a time for coincidence?

Mammals and birds appear to encode timing differences between the ears, a major cue for auditory localization, in fundamentally different ways. It now appears that results from different species can be accommodated within a single general framework.

Animals↗
PubMed1995

Neurons sensitive to interaural phase disparity in gerbil superior olive: diverse monaural and temporal response properties.

1. We assessed mechanisms of binaural interaction underlying detection of interaural phase disparity (IPD) by recording single-unit responses in the superior olivary complex (SOC) of the anesthetized gerbil (Meriones unguiculatus). Binaural responses were obtained from 58 IPD-sensitive single units, 44 of which were histologically localized. Monaural responses were also obtained for 52 of 58 IPD-sensitive units. Additionally, responses were recorded from 16 units (best frequency < 2.4 kHz) in lateral SOC that were excited by ipsilateral stimulation and inhibited by contralateral stimulation (EI), none of which was IPD sensitive. Our results are consistent with a mechanism of binaural interaction involving detection of coincident excitatory inputs from the two ears. There was no compelling evidence of binaural sensitivity arising from IPD-dependent interactions of phase-locked excitatory and inhibitory inputs from the two ears. Despite the uniformity of binaural interactions, considerable diversity of temporal and monaural response properties was observed. 2. Monaural and binaural responses of 35 of 58 IPD-sensitive units were phase locked to the period of low-frequency (< 2.5 kHz) tones. Most phase-locking units were bilaterally excitable and, consistent with the coincidence-detection model, their IPD selectivity could be predicted from the difference between the mean phases of the monaural responses. The remaining units (23 of 58) did not phase lock in response to monaural or binaural tones. Most non-phase-locking units failed to respond to monaural stimulation of one or both ears (monaurally unresponsive units). 3. Some IPD-sensitive units were inhibited by monaural stimulation of the ipsilateral ear or both ears. A few units responded only at the onset of monaural and binaural tones. Phase locking was present in responses of some, but not all, of these monaurally inhibited and onset units. 4. Most IPD-sensitive neurons were encountered at sites within or immediately adjacent to the cell column of the medial superior olive (MSO). IPD-sensitive units were also recorded in the lateral superior olive (LSO), in the superior paraolivary nucleus (SPN), and within a region forming a medial-dorsal cap around MSO. Bilaterally excitable unites were concentrated around MSO, but were also encountered in SPN, the medial-dorsal region, and LSO. Some monaurally unresponsive units were recorded in the vicinity of the MSO, but most were located in the medial-dorsal region. Monaurally inhibited units were localized to the medial border of the MSO cell column or to SPN. Onset units were localized to SPN and the medial-dorsal region. EI units were located exclusively in LSO.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗