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At least 217 records · Page 12Linked to original sources
PubMed2002

Vertical sound localization in blind humans.

It is widely held that early-blind people compensate their visual loss by a general sharpening of spatial hearing. The present study reports a possible exception to this view: when the vertical position (elevation) of a sound source had to be localized, four out of six early-blind subjects exhibited systematic deviations in pointing, while two early-blind subjects were as accurate as sighted controls. On the other hand, blind and sighted individuals were able to judge relative positions of different sound locations with similar precision. These results suggest that visual experience may be used to accurately calibrate the relation between the vertical coordinates of auditory space and body, but is not needed to develop sufficiently high resolution of spatial hearing.

Adult↗
PubMed1992

Adaptive adjustment of unit tuning to sound localization cues in response to monaural occlusion in developing owl optic tectum.

Bimodal units in the barn owl's optic tectum are tuned to the location of auditory and visual stimuli, and are systematically organized according to their spatial tuning to form mutually aligned maps of auditory and visual space. Map alignment results from the fact that, normally, units are tuned to the values of interaural level difference (ILD) and interaural time difference (ITD) produced by a sound source at the location of their visual receptive fields (VRFs). Monaural occlusion alters the correspondence of ILD and ITD values with locations in space. We investigated the effect that raising owls with a chronic monaural occlusion has on the tuning of tectal units to ILD and ITD. Owls were monaurally occluded beginning at 1 month of age. The effects of monaural occlusion were assessed 2-4 months later by comparing the ILD and ITD tuning of units in monaurally occluded owls with the ILD and ITD tuning of units with equivalent VRFs in normal owls. ILD and ITD tuning was shifted substantially and in the direction of the unoccluded ear (the adaptive direction) in owls raised with a monaural occlusion. In most tecta, the mapped representations of ILD and ITD were shifted systematically. In addition, in some tecta, monaural occlusion induced a change in the topography of the ILD map such that ILD tuning remained essentially constant at values near 0 dB over abnormally large portions of the tectum. Across all recording sites, the average shift in ILD tuning was 9 dB (n = 396) and the average shift in ITD tuning was 40 microseconds (n = 414). In four of five animals, the magnitude of the effect was not equivalent on the two sides of the brain, the adjustments being significantly larger and more systematic on the side ipsilateral to the occlusion. Such differences in the altered ILD and ITD maps on the two sides of the brain in individual animals indicate that, although a component of the adaptive adjustment might be due to regulation of the gain and phase response of the monaural signals early in the auditory pathway, a major component of the adjustment must occur at or beyond the level where the encoding of ILDs and ITDs for left and right space separates.

Adaptation, Physiological↗
PubMed1997

The nature and distribution of errors in sound localization by human listeners.

Measurement of localization performance will reflect errors that relate to the sensory processing of the cues to sound location and the errors associated with the method by which the subject indicates the perceived location. This study has measured the ability of human subjects to localize a short noise burst presented in the free field with the subject indicating the perceived location by pointing their nose towards the source. Subjects were first trained using a closed loop training paradigm which involved instantaneous feedback as to the accuracy of head pointing which resulted in the reduction of residual localization errors and a rapid acquisition of the task by the subjects. Once trained, 19 subjects localized between 4 and 6 blocks of 76 target locations. The data were pooled and the distribution of errors associated with each target location was examined using spherical methods. Errors in the localization estimates for about one third of the locations were rotationally symmetrical about their mean but the remaining locations were best described by an elliptical distribution (Kent distributed). For about one half of the latter locations the orientations of the directions of the greatest variance of the distributions were not aligned with the azimuth and elevation coordinates used for describing the spatial location of the targets. The accuracy (systematic errors) and the distribution of the errors (variance) in localization for our population of subjects were also examined for each test location. The size of the data set and the methods of analysis provide very reliable measures of important baseline parameters of human auditory localization.

Acoustic Stimulation↗
PubMed1996

Spectral cues for sound localization in cats: effects of frequency domain on minimum audible angles in the median and horizontal planes.

Rice et al. [Hear. Res. 58, 132-152 (1992)] classified directional properties of the cat's head-related transfer function (HRTF) into three frequency domains. Low frequencies (< 5 kHz) display a broad azimuth-sensitive spectral peak that establishes interaural level differences, mid frequencies (5-18 kHz) are marked with a single deep spectral notch that changes in frequency as a function of both azimuth and elevation, and high frequencies (18-50 kHz) exhibit a complex pattern of peaks and notches that shows extensive but less systematic changes with sound location. Spectral cues conveyed by the mid frequencies of broadband sounds are important in tasks that require cats to identify the actual location of acoustic stimuli [Huang and May, J. Acoust. Soc. Am. (in press)]. The present study investigates how directional cues conveyed by the mid- and high-frequency spectrum of the HRTF influence the cat's ability to discriminate between sound locations. Thresholds for spatial acuity were measured as minimum audible angles (MAAs) [Mills, J. Acoust. Soc. Am. 30, 237-246 (1958)] at positive azimuths in the interaural horizontal plane and at positive and negative elevations in the median vertical plane. The frequency domain of the noise burst had little effect on MAAs in the horizontal plane, but removal of high-frequency spectral information significantly increased thresholds at positive and negative elevations in the median plane. These results suggest that cats are sensitive to directional properties of the HRTF at frequencies above 18 kHz and may use this information to detect small changes in sound source elevation.

Animals↗
PubMed1996

Electrophysiological evidence of a sound localizing binaural subsystem in the human auditory brainstem.

The binaural interaction components of auditory brainstem evoked potentials reflect electrical changes which are specific to binaural stimuli. Analysis of these components indicated that different click lateralizations result in spatially distinct distributions of activity in the pons, but not at more peripheral levels. The effects of ipsilateral and binaural masking on evoked activity indicated distinct binaurally- and monaurally-activated neural subsets in the human brainstem. These results on the effects of noise and the distinct distributions of pontine activity to different lateralizations provide the first electrophysiological evidence that the auditory system in the humans pons includes a subset which is specific to binaurally presented sounds and which is anatomically distributed according to the lateralization of the sound. These results suggest auditory spatial mapping, similar to other sensory systems. In contrast to other systems, in which mapping is according to receptor distribution in the periphery, auditory spatial mapping is achieved computationally at central levels of the pathway.

Acoustic Stimulation↗
PubMed1981

Single-unit activity in the auditory cortex of monkeys actively localizing sound sources: spatial tuning and behavioral dependency.

Single-unit recordings were made from the auditory cortex of unanesthetized rhesus monkeys which were trained to perform a second localization task. Recordings were made from 196 units in 4 animals. Five sound sources were located at 0 degrees (midline) and on either side at azimuths of 37.5 degrees and 75 degrees. Almost most units responded to each of the 5 sources, 49% of the units had peak firing rates for the source on the contralateral side at 75% azimuth. Another 26% of the units had peak firing rates at the 37.5 degrees contralateral location, while only 11% had peak rates for the ipsilateral locations. In order to determine whether the behavior of actively locating a sound source affected units in auditory cortex, response rates compared under two behavioral conditions: one which required the detection of a sound regardless of location and another condition which required identification of a sound's location. of the 196 units, 16 had different response rates for the two conditions, with 15 of the 16 units having higher evoked rates in the localization task. For the 16 units, the difference in firing rate was typically observed for a single speaker location. No correlation could be determined between a unit's location within the subdivisions of auditory cortex and its spatial tuning response properties or its dependency upon behavioral condition.

Animals↗
PubMed1989

Binaural disparity cues available to the barn owl for sound localization.

1. Bilateral recording of cochlear potentials was used to measure the variations in interaural time differences (ITDs) and interaural intensity differences (IIDs) as a free-field auditory stimulus was moved to different positions around a barn owl's head. 2. ITD varied smoothly with stimulus azimuth across a broad frequency range. 3. ITD varied minimally with stimulus elevation, except at extreme angles from the horizontal. 4. IID varied with both stimulus elevation and stimulus azimuth. Lower frequencies were more sensitive to variations in azimuth, whereas higher frequencies were more sensitive to variations in elevation. 5. The loci of spatial coordinates that form iso-IID contours and iso-ITD contours form a non-orthogonal grid that relates binaural disparity cues to sound location.

Acoustic Stimulation↗
PubMed1991

[Sound localization in patients with asymmetrical hearing loss].

Good directional hearing ability demands good and symmetrical hearing in both ears. We report the effect of impaired hearing on the directional hearing ability of 98 patients, especially of patients with bilateral asymmetrical hearing loss. The directional testing device included 12 loudspeakers placed at 30 degree intervals in a circle with a diameter of 3.25 m, whose centre lay between the ears of the patient. In included an audiometer for producing the signals, an amplifier and a PDP11/23 computer interfaced to a loudspeaker switch bank. The subject's answers to 60 directionally randomized stimuli were recorded. During the presentation of the signal the patients were not allowed to turn their head. The patients had to name the number of the loudspeaker on the circle that they thought was producing the sound. In addition to the directional hearing test a pure-tone audiogram was done, and the middle- and high-frequency hearing loss estimated. The records of the directional hearing test were analysed in two new ways: firstly, vector analysis of the errors; secondly, averaging of the difference between the true interaural time delay and the virtual time difference, which was implicated in the possibly incorrect answer of the patient (effective delta-t-parameter). This average gives a score for the uncertainty in defining the correct "cone of confusion". In addition to the statistical analysis, two cases are reported showing the directional hearing ability of two patients with neuromas treated by transtemporal surgery, with some residual hearing.(ABSTRACT TRUNCATED AT 250 WORDS)

Audiometry↗
PubMed1999

Single cortical neurons serve both echolocation and passive sound localization.

The pallid bat uses passive listening at low frequencies to detect and locate terrestrial prey and reserves its high-frequency echolocation for general orientation. While hunting, this bat must attend to both streams of information. These streams are processed through two parallel, functionally specialized pathways that are segregated at the level of the inferior colliculus. This report describes functionally bimodal neurons in auditory cortex that receive converging input from these two pathways. Each brain stem pathway imposes its own suite of response properties on these cortical neurons. Consequently, the neurons are bimodally tuned to low and high frequencies, and respond selectively to both noise transients used in prey detection, and downward frequency modulation (FM) sweeps used in echolocation. A novel finding is that the monaural and binaural response properties of these neurons can change as a function of the sound presented. The majority of neurons appeared binaurally inhibited when presented with noise but monaural or binaurally facilitated when presented with the echolocation pulse. Consequently, their spatial sensitivity will change, depending on whether the bat is engaged in echolocation or passive listening. These results demonstrate that the response properties of single cortical neurons can change with behavioral context and suggest that they are capable of supporting more than one behavior.

Animals↗
PubMed1989

Sound localization, use of binaural cues and the superior olivary complex in pigs.

Noise localization thresholds and the ability to localize pure tones at 60 degrees separation were determined for three domestic pigs using a conditioned avoidance procedure. The average threshold for localizing a brief noise burst was 4.5 degrees which is much more accurate than the thresholds of other hoofed mammals, such as horses, cattle and goats. The ability of pigs to localize low-frequency tones indicates that they can use the binaural phase-difference cue. However, they were unable to localize tones of 4 kHz and higher, indicating that, like other hoofed mammals, their ability to use binaural intensity cues is greatly restricted if not completely absent. An examination of the superior olivary complex of pigs revealed that in relative size, shape and cell density it is more like that of cats than that of other hoofed mammals.

Animals↗
PubMed2002

Listener weighting of cues for lateral angle: the duplex theory of sound localization revisited.

The virtual auditory space technique was used to quantify the relative strengths of interaural time difference (ITD), interaural level difference (ILD), and spectral cues in determining the perceived lateral angle of wideband, low-pass, and high-pass noise bursts. Listeners reported the apparent locations of virtual targets that were presented over headphones and filtered with listeners' own directional transfer functions. The stimuli were manipulated by delaying or attenuating the signal to one ear (by up to 600 micros or 20 dB) or by altering the spectral cues at one or both ears. Listener weighting of the manipulated cues was determined by examining the resulting localization response biases. In accordance with the Duplex Theory defined for pure-tones, listeners gave high weight to ITD and low weight to ILD for low-pass stimuli, and high weight to ILD for high-pass stimuli. Most (but not all) listeners gave low weight to ITD for high-pass stimuli. This weight could be increased by amplitude-modulating the stimuli or reduced by lengthening stimulus onsets. For wideband stimuli, the ITD weight was greater than or equal to that given to ILD. Manipulations of monaural spectral cues and the interaural level spectrum had little influence on lateral angle judgements.

Cues↗
PubMed1998

Pinna movements of the cat during sound localization.

We measured the movements of the external ear, or pinna, using the magnetic search coil technique in cats trained to look at auditory and visual targets for a food reward. No behavioral contingencies were placed on pinna movements. Prominent pinna movements accompany eye movements when the animal orients to either auditory or visual stimuli. In visual trials the pinna movements are coordinated with eye movements, suggesting that they are part of the general orientation response of the animal. In auditory trials the pinna response was composed of two movements: short- and long-latency components. Whereas the long-latency component seemed to occur with the eye movement to the target, the short-latency component was coupled to the onset of the stimulus. The short-latency component ( approximately 25 msec) was highly asymmetrical, being largest in the pinna ipsilateral to the stimuli. In one animal it persisted after >10(5) trials.

Acoustic Stimulation↗
PubMed1981

Peripheral basis of sound localization in anurans. Acoustic properties of the frog's ear.

Directional responses of single auditory fibers in the eighth nerve of northern leopard frogs (Rana pipiens) were studied in order to gain some insights into the acoustical properties of the frog's ear. In addition to the actual directional response of a fiber, a theoretical directional-response curve to the intensity-rate function of the unit. The difference in the two responses provided a measure of the directional characteristics of the frog's ear at the stimulating frequency which can be plotted in a polar diagram to show the directivity pattern of the frog's acoustic receiver. Directivity patterns were obtained from three groups of experimental animals under the following conditions: (I) mouth filled with moistened cotton; (II) contralateral ear coated with silicone rubber cement; (III) open mouth. Changes in the directivity patterns were observed with experimental manipulations and these were compared to those obtained from normal animals (Feng, A.S. (1980) J. Acoust. Soc. AM. 68, 1107-1114). The results suggest that the frog's ear behaves as a combination pressure-pressure gradient receiver.

Animals↗
PubMed1981

Earmuffs, exploratory head movements, and horizontal and vertical sound localization.

In a semi-anechoic room, normal-hearing adults judged the position of that loudspeaker emitting a narrow-band noise centered at 1 kc/s, from a vertical array of 10 loudspeakers in 18 degrees steps, or a similar horizontal-arc array intersecting at 0 degrees azimuth and 0 degrees vertical. Stimuli were narrow-band noise bursts terminated by S when judgment was made. Ss (N:17) were free to move their heads, or were asked to restrict such movement. In the horizontal plane, Ss without earmuffs and with free head movement performed with 95% absolute accuracy but, with earmuffs, accuracy fell off to 50%, and when head movements were restricted accuracy fell off further to 24%. The results of Fisher and Freeman (J. Aud. Res., 1968, 8, 15-26) were generally confirmed, but free head movements did not, as in their study, totally "wash out" functional pinna removal. In the vertical plane, Ss with earmuffs even with free head movements yielded only 19% absolute accuracy, though without earmuffs accuracy rose to 72%. A postulate arising from this study is that listeners are unable to recruit remaining (interaural) cues when these are generated under different bodily orientations. The potential practical hazard suggested by the results is noted.

Auditory Perception↗
PubMed1990

The auditory periphery of the ferret. II: The spectral transformations of the external ear and their implications for sound localization.

In the previous paper the directional response characteristics of the ferret auditory periphery were examined. In this study further measurements of the spectral transfer functions (STFs) of the auditory periphery were obtained at locations close to the tympanic membrane. There was considerable variation in the STFs recorded from different animals and between recordings made at each end of the auditory canal in the same animal. However, calculation of the so called "location dependency function" demonstrated that changes in the location of the stimulus produced the same pattern of changes in the STFs in all recordings. Changes in the spectral transformation for azimuth locations in the ipsilateral auditory field were examined by calculating the horizon STF. The gain transformations of frequencies below 20 kHz were found to be asymmetrical about the interaural axis so that maximum gain was obtained for anterior stimulus locations. In contrast, the maximum gain for frequencies above 20 kHz was obtained for stimulus locations about the interaural axis, and movement of the stimulus location into either the anterior or posterior fields produced symmetrical reductions in gain. These changes were related to the directional properties of the periphery examined in the previous paper [S. Carlile, J. Acoust. Soc. Am. 88, 2180-2195 (1990)]. The spatial resolution of the monaural information provided by the peripheral STFs is dependent on the rate of change of the transformations as a function of azimuthal displacement of the stimulus location. This was examined by calculating the unsigned first spatial derivative for each frequency in the horizon STF.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Vision-independent adjustment of unit tuning to sound localization cues in response to monaural occlusion in developing owl optic tectum.

Neurons in the developing optic tectum adjust their tuning to auditory localization cues in response to chronic monaural occlusion so that auditory spatial fields align with visual receptive fields (VRFs). We tested whether this adaptive adjustment of auditory tuning requires visual instruction. Both eyelids were sutured closed at the same time that one ear was occluded in two barn owls that were 1 month old. After 70 and 100 d, respectively, the tuning of units to interaural level difference (ILD) and to interaural time difference (ITD) was measured. These data were compared with equivalent data from 15 normal owls. Unit tuning to ITD was shifted from normal in both of the monaurally occluded owls. In one owl, ILD tuning was also clearly shifted. In the other owl, the map of ILD was flipped upside down and adaptive adjustments in ILD tuning could not be assessed. Instead, adjustments in ILD tuning were observed following removal of the earplug with the eyelids kept closed. Unit tuning was monitored at several sites in the tectum for 1 month after earplug removal using chronically implanted electrodes. Then, ILD tuning was resampled across the entire tectum. Both measures indicated shifts in ILD tuning in response to removal of the earplug in the second blind owl. In both animals, the magnitude of the shifts in ILD tuning and ITD tuning was smaller than has been observed previously in monaurally occluded but sighted owls. The results demonstrate that the brain can make adaptive adjustments in ILD and ITD tuning in response to early monaural occlusion even without the guiding influence of vision.

Adaptation, Physiological↗
PubMed1996

Sound localization in chinchillas, III: Effect of pinna removal.

The ability of chinchillas to make left/right, front/back, and vertical locus discriminations was determined before and after surgical removal of the pinnae. The animals were tested behaviorally using a conditioned avoidance procedure. In the left/right localization tests, removal of both pinnae had no effect on localization acuity for broadband noise but did result in a small decrement in performance when localizing low-pass filtered noise. In the front/back localization tests, removal of a single pinna resulted in a small but consistent decrement in performance when the sound sources were located in the hemifield on the same side as the intact pinna, and a greater decrement when the sound sources were located in the hemifield on the side of the missing pinna; removal of both pinnae resulted in the largest decrement in performance. Finally, vertical localization acuity and performance when localizing low-pass filtered noise were greatly impaired following removal of both pinnae. These results demonstrate the importance of the pinnae in performing front/back and vertical localization tasks in which binaural cues are not available.

Acoustic Stimulation↗