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At least 199 records · Page 11Linked to original sources
PubMed1984

A developmental look at an auditory illusion: the precedence effect.

Infants aged 2 and 6 months were tested with the precedence effect, an auditory phenomenon involving sound localization. Each infant was tested with two types of stimuli: sound from a single loudspeaker and precedence-effect sounds produced by the same sound put through two loudspeakers, with one output leading the other by 7 msec. Older infants localized precedence-effect stimuli as they did single-source stimuli, indicating that they perceived this phenomenon as expected. Two-month-olds turned their heads toward single-source sounds, but did not localize precedence-effect sounds, suggesting that that more difficult perceptual task had not been achieved at this age. In general, head-turning toward sound proved far more difficult to elicit in younger infants. A click train was ineffective, but a tape-recorded human voice elicited above-chance low-level turning. The developmental changes in auditory behavior are discussed in terms of the rapid growth of the auditory cortex.

Arousal↗
PubMed1989

Mismatch negativity to change in spatial location of an auditory stimulus.

Auditory stimulus blocks were presented to 12 reading subjects. Each block consisted of 2 types, standard (P = 90%) and deviant stimuli (P = 10%), delivered in a random order. The only difference between these stimuli was their spatial location of origin. The subject always heard the standards as coming straight in front and the deviants from an angle of either 10, 45, or 90 degrees to the right of the standards. The spatial locations were produced via earphones by introducing for low-frequency (600 Hz) tones an interaural phase difference and for high-frequency (3000 Hz) tones an interaural intensity difference. Standard and deviant stimuli were also delivered in more natural, free-field, conditions via differently positioned loudspeakers. The deviant tones elicited an event-related brain potential component called the mismatch negativity (MMN), followed by a P3a component. Thus changes in spatial location of an auditory stimulus produced by following either one of the two main principles of human sound localization elicited the MMN. Consequently, it was concluded that the spatial location of a sound source is coded in the hypothesized neuronal stimulus traces reflected by the MMN and, further, that a change in this location is automatically detected by the brain by means of the MMN generator process.

Adult↗
PubMed1990

Auditory localization: effects of reflecting surfaces.

Based on anatomical and evolutionary conceptions of the human ear, an experiment was conducted in which forty-eight human subjects were asked to localize sounds (a human voice) emitted by one of twenty-seven stationary loudspeakers in an anechoic chamber. The position of the active loudspeaker varied with respect to azimuth, distance, and elevation in three steps each. The position of a single sound-reflecting surface (about 6 m2) was varied: on the floor, on the ceiling, to the left, and to the right. The accuracy of identifying the active loudspeaker for each position of the sound-reflecting surface was compared intraindividually with the absence of reflection. The results show an overall increase in correct localizations with a sound-reflecting surface on the floor. Especially the elevation of the sound source can be detected with greater precision. Additionally, the percentage of correct localizations decreased systematically with the presence of a sound-reflecting ceiling, while the presence of sound-reflecting walls did not systematically affect the localization performance. Judgments in the horizontal plane and those of distance were not systematically influenced by the presence of a sound-reflecting surface.

Adult↗
PubMed1992

Azimuthal processing in the posterior auditory thalamus of cats.

The responses to free-field acoustic stimuli of 157 units in the auditory thalamus of anesthetized cats were studied in relation to the localization of pure tone stimuli in the azimuthal plane. Units were classified as 'directional' if their firing rates at sound levels in excess of 20 dB above threshold varied by more than 50% as a function of azimuth. Sixty-five % of the units in the nucleus of the brachium of the inferior colliculus and 30% in the ventral division of the medial geniculate body were found to be directional, suggesting different processing channels for sound localization between colliculus and cortex.

Acoustic Stimulation↗
PubMed1992

Altitude-dependent changes of directional hearing in mountaineers.

This study demonstrates apparent deterioration in the ability to localize sound associated with acute exposure to high altitude in ten subjects on three mountaineering expeditions. Furthermore, the auditory localization errors improved to sea level values after a period of acclimatization. Occurring at altitudes where overt neurological symptoms are not usually seen, impairment of sensory perception may explain the increase in accidental deaths associated with altitude exposure due to disorientation and misjudgment but before hypoxia is evident.

Acclimatization↗
PubMed1988

Hearing in the ferret (Mustela putorius): effects of primary auditory cortical lesions on thresholds for pure tone detection.

1. Pure tone thresholds were determined for five adult male ferrets before and after bilateral ablation of primary auditory cortex. Complete audiograms ranging from 0.016 to 48 kHz were obtained for two animals. The remaining three animals were tested at five frequencies selected to assess hearing throughout the audible range (0.125, 0.5, 2.0, 8.0, and 32.0 kHz). 2. Shortly after surgery one animal had elevated thresholds across the entire frequency range with the most pronounced hearing loss above 12.0 kHz. Four other animals had no elevation of thresholds at low and midrange frequencies but suffered a hearing loss at very high frequencies (32 kHz). 3. Repeated testing over a period of several months revealed substantial recovery of sensitivity. There was complete recovery of sensitivity in the low- and middle-frequency range of the audiogram. Some hearing loss persisted at the extreme upper end of the audiogram (32 kHz), but in two cases there was evidence of recovery at this frequency as well. 4. Following determination of absolute thresholds all animals were assessed for their ability to localize sound in space. Minimum audible angles were obtained on midline as well as within both left and right hemifields, i.e., around 0, -60 and +60 degrees azimuth. All animals had severe and persistent deficits in their ability to localize brief sounds within the lateral fields, but were still capable of midline localization.

Animals↗
PubMed1987

Localization of noise, use of binaural cues, and a description of the superior olivary complex in the smallest carnivore, the least weasel (Mustela nivalis).

Cats and dogs have relatively good sound-localization acuity, and the question arises as to whether this trait is a characteristic of all carnivores or whether it is due to the fact that they have large heads and correspondingly large binaural localization cues available to them. The localization acuity of the least weasel, the smallest extant carnivore, was found to be less accurate than larger carnivores but more accurate than other small mammals. This suggests that carnivores may be under strong selective pressure to localize accurately but that interaural distance may be a limiting factor. The least weasel is capable of using both binaural phase differences and intensity differences to localize, but has a relatively broad mid-frequency range for which neither cue is optimal. Finally, the superior olivary complex of the least weasel is well developed and resembles that of larger carnivores more than that of small rodents.

Animals↗
PubMed1991

The auditory periphery of the ferret: postnatal development of acoustic properties.

The development of the acoustics of the auditory periphery of the ferret was examined by measuring the spectral transfer functions (STFs) and the directional characteristics of the outer ears of animals ranging in age from postnatal day 32 (P32) to P54. Using an impulse response technique the STFs were obtained from up to 250 locations throughout free space. The directional responses were calculated for frequencies between 1 kHz and 30 kHz. The low frequency roll-off of the STF decreased with increasing age from around 15 kHz at P32 to an adult value of around 8 kHz by P51. The directional responses of the outer ear of the immature ferrets differed significantly from adult animals in a fashion that was consistent with the smaller size of the auditory periphery. However, by P51 the responses were generally within the normal adult range. The implications of the relatively rapid development of the acoustics of the auditory periphery are discussed in terms of the development of mechanisms subserving sound localization.

Acoustic Stimulation↗
PubMed1977

[Objective determinations of individual sound protectors (author's transl)].

A method for objective measurements of the sound attenuation provided by ear protectors is described, utilizing a head model which contains all normal human sound properties. The difficulties experienced in localizing sound sources when wearing ear protectors is explained by changing the characteristics of the individual frequency bands.

Ear Protective Devices↗
PubMedDate not supplied

[Role of higher divisions of the auditory system in localizing a moving sound source].

Impairment of the ability to localize a moving acoustic image was studied in animal (dogs) following experimental ablation of the auditory cortical areas, and in patients following unilateral electro-shock seizures and focal injuries of the temporal cortex. Unilateral ablation of AI, AII and Ep areas in animals produces a disturbance in differentiation of parameters of a moving acoustic image, while a bilateral ablation results in disappearance of the ability to localize the image. After left-side electro-shock seizures in the patients, localization of movement of the acoustic image did not differ from the normal, while after right-side seizures, the trajectory of the image movement was sharply shortened and shifted to the right. In the case of a focal injury of the patient's left hemisphere, localization changes were of a diffuse nature (shortened trajectory of movement both on the right and left side). In the case of a right-side focus, the trajectory of the movement of the acoustic image on the side of the lesion did not differ from the normal, while on the opposite side it was sharply shortened and shifted towards the mid-line of the head. The conclusion has been made that there is a specialization in the human right hemisphere in achieving spatial hearing, while it is absent in animals.

Animals↗
PubMed1992

Directionality of phase locking in auditory nerve fibers of the leopard frog Rana pipiens pipiens.

A dorsal approach to the eighth nerve and free-field stimulation were used to investigate the effect of sound direction and intensity on phase locking in auditory nerve fibers of the leopard frog Rana pipiens pipiens. Tuning curves of 75 auditory neurons were analyzed (Fig. 2). Amphibian papillar neurons, but not basilar papillar neurons, exhibit significant phase locking to short tone bursts at the characteristic frequency (CF), the degree of phase locking (vector strength) decreasing with the neuron's CF (Figs. 3, 4 and 10E). Vector strength increases with sound pressure level to saturate about 20 dB above threshold, while the preferred firing phase is only slightly affected (Figs. 5 and 6). In contrast, sound direction hardly affects vector strength (Figs. 7, 8, 9A and 10A and C), but has a strong influence on the preferred firing phase (Figs. 7, 8, 9B and C, 10B and D): With respect to anterior tone presentation there are phase lags for ipsilateral and phase leads for posterior and contralateral presentation. Phase differences between both ears show a sinusoidal or cardioid/ovoidal directional characteristic; maximum differences are found with antero-lateral tone presentation (Fig. 11). The directionality of phase locking decreases with the neuron's CF (Fig. 10F) and only slightly changes with sound pressure level (Fig. 12). Thus, phase locking of amphibian papilla neurons can potentially provide intensity-independent information for sound localization.

Acoustic Stimulation↗
PubMed1990

[Directional hearing in relation to individual circadian biorhythm].

Acuity angle of the directional hearing was investigated in connection with the individual circadian rhythm. Two groups of 15 persons represented the morning and evening form of the circadian rhythm. Body temperature fixed the rhythm character. The evaluations of the angle acuity of the directional hearing were performed in the highest and the lowest point of body temperature as well as in the neutral point, which was determined in the morning group in the middle between the two extremes. The possibility of the sound localization in individual and linked with the body temperature circadian rhythm.

Acoustic Stimulation↗
PubMed1986

An acoustic approach to diver navigation.

Three experiments were carried out to assess the capability of divers to localize acoustic signals underwater and to navigate by them. In the first experiment, divers attempted to determine the correct distance to several underwater transducers projecting acoustic stimuli on a horizontal plane. The second experiment consisted of two related studies where the diver/subjects attempted to discover which of many possible stimuli would produce the most robust perception of underwater "sound movement," or the Underwater Auditory Phi Phenomenon (UAPP). A third experiment consisted of navigational swims by divers; the acoustic stimuli utilized were based on those identified in prior experiments as the most preferred. The results demonstrated that divers are able to discriminate among signals emanating from acoustic sources at various distances underwater and to do so at levels well above chance. Second, divers judged 500-Hz square waves to be the signal which best facilitated an acceptable UAPP; thermal noise and 1-kHz square waves followed in that order. However, these differences were only slight and, in practice, divers maintained that the noise signal was the most useful. Third, it was found that divers apparently can effectively navigate by means of auditory signals alone--at least within certain limits. Finally, a significant decrease in the discrimination abilities of divers for frequencies above 6 kHz suggests that intensity cues may not be as robust as time-of-arrival information with respect to underwater sound localization.

Acoustic Stimulation↗
PubMed1990

Directional dependence of interaural envelope delays.

Interaural envelope delays were measured in six human subjects as a function of the location of a movable sound source, bandpassed between 3 and 16 kHz. A total of 324 source locations were tested in horizontal and vertical increments of 10 degrees. A method is described for estimating the complex directional transfer function of the external ear, independent of the position of the recording microphone in the ear canal. To compute interaural envelope delays, directional transfer functions from the left and right ears were convolved with a critical-band filter, the envelopes were computed, and the envelopes were cross correlated. Interaural envelope delays, as well as interaural group delays, varied somewhat with the center frequency of the critical-band filter and with the vertical location of the sound source. Nevertheless, to a first approximation, envelope delays measured in the ear canals increased monotonically with increasing angle of incidence relative to the median plane, as they would for two microphones on the surface of a rigid sphere. The results are discussed in relation to the possible contribution of interaural envelope delays to sound localization behavior.

Attention↗
PubMed1992

Neural derivation of sound source location: resolution of spatial ambiguities in binaural cues.

Cues for sound localization are inherently spatially ambiguous. Nevertheless, most neurons in the barn owl's optic tectum (superior colliculus) have receptive fields for broadband noise stimuli that are restricted to a single region of space. This study characterizes the spatial ambiguities associated with two important sets of localization cues, interaural level differences (ILDs) and interaural phase differences (IPDs), and describes how information is integrated within and across frequencies to resolve these ambiguities. The auditory receptive fields of neurons in the optic tectum were measured with free-field sounds presented from a movable loudspeaker. In contrast to the single regions typical for broadband receptive fields, receptive fields for tonal stimuli usually included additional discrete regions of space (accessory fields). Based on acoustic measurements of ILD and IPD cues made in the external ear canals, it was shown that accessory fields corresponded to locations from which sound sources produced ILD and IPD values that were approximately the same as those arising from the broadband receptive field. In addition, accessory fields had inhibitory surrounds, corresponding to locations from which sound sources produced substantially different combinations of ILD and IPD values. Where an accessory field for one frequency overlapped with the inhibitory surround of a second frequency, an excitatory response to the first frequency could be reduced or eliminated by addition of the second frequency. Because tonal receptive fields for different frequencies always overlapped in the region of the broadband receptive field but tended not to overlap elsewhere, this integration of excitation and inhibition can account for the restriction of broadband receptive fields to a single region of space.

Animals↗
PubMed1984

Binaural interactions of single neurons in posterior field of cat auditory cortex.

In the auditory cortex of barbiturate-anesthetized cats, the posterior auditory field (area P) was identified by its tonotopic organization, and single neurons in that field were studied quantitatively with regard to their binaural interactions at their respective best frequencies, using calibrated, sealed stimulating systems. Almost 60% of the neurons studied displayed " summative " binaural interactions in that their responses to binaural, equally intense stimulation of the two ears were stronger than were their responses to monaural stimuli of the same intensity. For these neurons, latent periods were shorter for binaural stimuli than for monaural stimuli. Some field P neurons were sensitive to interaural intensity disparities and manifested that sensitivity in one of two forms. Cells that were excited by stimulation of one ear and inhibited by stimulation of the other typically displayed a sigmoidal relation of spike count to intensive disparity, with spike counts being larger when the disparity favored the contralateral ear. Cells that were unresponsive to monaural stimuli but responded securely to binaural stimuli usually displayed a peaked, nonmonotonic relation of spike count to interaural intensity disparity, with maximal responses being elicited by stimuli with zero or near-zero disparity. Some neurons of low best frequency were sensitive to variations in interaural phase delay. In all cases, this sensitivity was manifested as a cyclical relation of spike count to interaural delay, with the period of the cycle being that of the stimulating tone. The fact that the binaural interactions of field P neurons were similar to those of cells in the primary auditory cortex suggests that the previously described heightened spectral-amplitude selectivity of field P neurons has been achieved without cost to their sensitivity to a variety of parameters of binaural stimulation. The particular sensitivity of cortical neurons to variations in interaural disparities associated with midline or near-midline azimuths might constitute a neural mechanism for the behavioral finding that animals and humans show their greatest acuity in sound localization for stimulus locations in or near the midsagittal plane.

Animals↗
PubMed1991

Auditory cortex: comparative aspects of maps and plasticity.

Much recent work in the field of auditory cortex analysis consists of an intensified search for complex sound representation and sound localization mechanisms using tonotopic maps as a frame of reference. Mammalian species rely on parallel processing in multiple tonotopic and non-tonotopic maps but show different degrees of unit complexity, and orderly representation of acoustic dimensions in such maps depending on the predictability of sounds in their environment. Birds appear to rely chiefly on one tonotopic map which harbours multidimensional complex representations. During development and after partial hearing loss, tonotopic organization changes in a predictable manner. Learning also modifies the spatial representation of sounds and even modifies tonotopic organization, but the spatial rules involved in this process have not yet emerged.

Animals↗
PubMed1990

Direction-dependent spectral properties of cat external ear: new data and cross-species comparisons.

Free-field to eardrum transfer functions were measured in anesthetized cats inside an anechoic chamber. Direction-dependent transformations were determined by measurement of sound-pressure levels using a small probe tube microphone surgically implanted in a ventral position near the tympanic membrane. Loudspeaker and probe microphone characteristics were eliminated by subtraction of the signal recorded in the free field with no animal present. Complexities of the transfer function, which include the presence of prominent spectral notches in the 8- to 18-kHz frequency region, are due primarily to the acoustical properties of the pinna. Differential amplification of frequency components within the broadband stimulus occurs as a function of source direction. Spectral features vary systematically with changes in both elevation (EL) and azimuth (AZ). The contrast between a notch and its shoulders is enhanced in the interaural spectral records. Spectral data from single source locations and spatial data for single frequencies at many locations are presented and comparisons with other species are drawn. It is suggested that spectral features in the 8- to 18-kHz region provide some of the necessary spectral information for sound localization and that the contrast in spectral energy between the frequencies at the notch and its shoulders is a potential directional cue.

Acoustic Stimulation↗