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

Cortical neurons that localize sounds.

Efforts to locate a cortical map of auditory space generally have proven unsuccessful. At moderate sound levels, cortical neurons generally show large or unbounded spatial receptive fields. Within those large receptive fields, however, changes in sound location result in systematic changes in the temporal firing patterns such that single-neuron firing patterns can signal the locations of sound sources throughout as much as 360 degrees of auditory space. Neurons in the cat's auditory cortex show accurate localization of broad-band sounds, which human listeners localize accurately. Conversely, in response to filtered sounds that produce spatial illusions in human listeners, neurons signal systematically incorrect locations that can be predicted by a model that also predicts the listeners' illusory reports. These results from the cat's auditory cortex, as well as more limited results from nonhuman primates, suggest a model in which the location of any particular sound source is represented in a distributed fashion within individual auditory cortical areas and among multiple cortical areas.

Animals↗
PubMed1992

The dominant role of low-frequency interaural time differences in sound localization.

Two experiments are described in which listeners judge the apparent directions of virtual sound sources-headphone-presented sounds that are processed in order to simulate free-field sounds. Previous results suggest that when the cues to sound direction are preserved by the simulation, the apparent directions of virtual sources are nearly the same as the apparent directions of real free-field sources. In the experiments reported here, the interaural phase relations in the processing algorithms are manipulated in order to produce stimuli in which the interaural time difference cues signal one direction and interaural intensity and pinna cues signal another direction. The apparent directions of these conflicting cue stimuli almost always follow the interaural time cue, as long as the wideband stimuli include low frequencies. With low frequencies removed from the stimuli, the dominance of interaural time difference disappears, and apparent direction is determined primarily by interaural intensity difference and pinna cues.

Adult↗
PubMed2003

Speech segregation based on sound localization.

At a cocktail party, one can selectively attend to a single voice and filter out all the other acoustical interferences. How to simulate this perceptual ability remains a great challenge. This paper describes a novel, supervised learning approach to speech segregation, in which a target speech signal is separated from interfering sounds using spatial localization cues: interaural time differences (ITD) and interaural intensity differences (IID). Motivated by the auditory masking effect, the notion of an "ideal" time-frequency binary mask is suggested, which selects the target if it is stronger than the interference in a local time-frequency (T-F) unit. It is observed that within a narrow frequency band, modifications to the relative strength of the target source with respect to the interference trigger systematic changes for estimated ITD and IID. For a given spatial configuration, this interaction produces characteristic clustering in the binaural feature space. Consequently, pattern classification is performed in order to estimate ideal binary masks. A systematic evaluation in terms of signal-to-noise ratio as well as automatic speech recognition performance shows that the resulting system produces masks very close to ideal binary ones. A quantitative comparison shows that the model yields significant improvement in performance over an existing approach. Furthermore, under certain conditions the model produces large speech intelligibility improvements with normal listeners.

Adult↗
PubMed2001

Three-dimensional sound localization from a compact non-coplanar array of microphones using tree-based learning.

One of the various human sensory capabilities is to identify the direction of perceived sounds. The goal of this work is to study sound source localization in three dimensions using some of the most important cues the human uses. In an attempt to satisfy the requirements of portability and miniaturization in robotics, this approach employs a compact sensor structure that can be placed on a mobile platform. The objective is to estimate the relative sound source position in three-dimensional space without imposing excessive restrictions on its spatio-temporal characteristics and the environment structure. Two types of features are considered, interaural time and level differences. Their relative effectiveness for localization is studied, as well as a practical way of using these complementary parameters. A two-stage procedure was used. In the training stage, sound samples are produced from points with known coordinates and then are stored. In the recognition stage, unknown sounds are processed by the trained system to estimate the 3D location of the sound source. Results from the experiments showed under +/-3 degrees in average angular error and less than +/-20% in average radial distance error.

Computer Systems↗
PubMed2006

Phase locking of auditory-nerve fibers to the envelopes of high-frequency sounds: implications for sound localization.

Although listeners are sensitive to interaural time differences (ITDs) in the envelope of high-frequency sounds, both ITD discrimination performance and the extent of lateralization are poorer for high-frequency sinusoidally amplitude-modulated (SAM) tones than for low-frequency pure tones. Psychophysical studies have shown that ITD discrimination at high frequencies can be improved by using novel transposed-tone stimuli, formed by modulating a high-frequency carrier by a half-wave-rectified sinusoid. Transposed tones are designed to produce the same temporal discharge patterns in high-characteristic frequency (CF) neurons as occur in low-CF neurons for pure-tone stimuli. To directly test this hypothesis, we compared responses of auditory-nerve fibers in anesthetized cats to pure tones, SAM tones, and transposed tones. Phase locking was characterized using both the synchronization index and autocorrelograms. With both measures, phase locking was better for transposed tones than for SAM tones, consistent with the rationale for using transposed tones. However, phase locking to transposed tones and that to pure tones were comparable only when all three conditions were met: stimulus levels near thresholds, low modulation frequencies (<250 Hz), and low spontaneous discharge rates. In particular, phase locking to both SAM tones and transposed tones substantially degraded with increasing stimulus level, while remaining more stable for pure tones. These results suggest caution in assuming a close similarity between temporal patterns of peripheral activity produced by transposed tones and pure tones in both psychophysical studies and neurophysiological studies of central neurons.

Acoustic Stimulation↗
PubMed1987

The effect of cerebrovascular accident on the ability to localize sounds under conditions of the precedence effect.

This study examines the ability of patients with cerebrovascular accident to localize single clicks and assign spatial locations to paired clicks presented from loudspeakers on the left and right of midline. The clicks within each pair were separated by intervals of either 2, 4, 8, or 16 msec. Normal subjects and brain-damaged patients without evidence of discrete lesions in their CT scans were able to localize both single and paired clicks. Patients with discrete right temporo-parietal lobe lesions were able to localize single clicks, but frequently reversed the apparent perceptual locus of paired clicks in the hemifield contralateral to the side of lesion. Patients with lesions in the left hemisphere, in areas outside the temporo-parietal region, did not display deficits under any condition.

Acoustic Stimulation↗
PubMed1996

An artificial neural network for sound localization using binaural cues.

A three-layer neural network is used to estimate the direction of a sound source from the signals detected by two directional, spatially separate receivers. Although the implemented system does not require any specific knowledge about acoustical parameters or propagation properties, a model of the acoustical environment is used to generate simulated data for training the network. The neural network is trained according to the multiple extended Kalman algorithm (MEKA), which provides fast convergence and does not require intervention for adjustment of the learning parameters. Lower bounds on estimation are computed and compared with simulations using the neural network.

Acoustics↗
PubMed1988

Sound localization and use of binaural cues by the gerbil (Meriones unguiculatus).

Noise-localization thresholds and the ability to localize pure tones at 60 degrees separation were determined for gerbils. The gerbils were trained using a two-choice procedure with observing response in which the gerbils made a left or right response to sounds emanating from their left or right side in order to obtain food. The average 75% correct localization threshold of 7 gerbils for a 100-ms noise burst was 27 degrees with chance performance (p greater than .01) reached at 12 degrees. The ability of 4 gerbils to localize both low- and high-frequency pure tones indicates that gerbils are able to use both phase- and intensity-difference locus cues. The frequency at which tone localization was poorest was 2.8 kHz, well below the theoretical frequency of ambiguity of the phase cue but within the frequency range at which phase locking declines in the mammalian auditory system. The sound localization ability of gerbils is typical of small rodents, and there is no obvious sign that it is affected by the degenerative disorder of the central auditory system which has been recently discovered in gerbils.

Animals↗
PubMed1998

Sound localization in the median sagittal plane by listeners with presbyacusis.

In Experiment 1, a group of listeners with substantial hearing loss due to presbyacusis and a group of listeners with normal hearing were given three localization tests: a frontal plane test in which they judged whether sounds came from the left, overhead, or the right; a sagittal plane test in which they judged whether sounds came from directly in front, overhead, or behind; and an elevation test in which they judged the vertical position of sounds coming from in front. The two groups performed similarly on the frontal plane test, which chiefly depended upon their ability to use binaural localization cues. They performed differently on the sagittal plane and elevation tests, for which the predominant localization cues were spectral. The listeners with presbyacusis were substantially less accurate than those with normal hearing in both of these instances. They had particular difficulty judging source elevation, rarely scoring much above chance. Follow-up testing of a group of subjects in the early stages of presbyacusis showed localization performance that was intermediate to the other two groups, but far more like that of the normal-hearing listeners. In Experiment 2, additional tests were run with the following conditions designed to encourage improved performance by listeners with presbyacusic hearing loss: (1) filtering of stimuli to preclude masking of more informative high-frequency components by low frequencies; (2) simplification of the elevation test and greater spatial separation of its loudspeaker sources; and (3) use of hearing aids. Conditions 1 and 2 had no appreciable effect on performance; condition 3 significantly improved presbyacusic listeners' ability to localize in the sagittal plane, particularly when sounds came from the front.

Adult↗