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At least 235 records · Page 13Linked to original sources
PubMed1994

Simulation of free-field sound sources and its application to studies of cortical mechanisms of sound localization in the cat.

We synthesized a set of signals (clicks) for earphone delivery whose waveforms and amplitude spectra, measured at the eardrum, mimic those of sounds arriving from a free-field source. The complete stimulus set represents 1816 sound-source directions, which together surround the head to form a 'virtual acoustic space' for the cat. Virtual-space stimuli were delivered via calibrated earphones sealed into the external meatus in cats under barbiturate anesthesia. Neurons recorded in AI cortex exhibited sensitivity to the direction of sound in virtual acoustic space. The aggregation of effective sound directions formed a virtual space receptive field (VSRF). At 20 dB above minimal threshold, VSRFs fell into one of several categories based on spatial dimension and location. Most VSRFs were confined to either the contralateral (59%) or ipsilateral (10%) sound hemifield. Seven percent spanned the frontal quadrants and 16% were omnidirectional. Eight percent fit into no clear category and were termed 'complex'. The size, shape, and location of VSRFs remained stable over many hours of recording. The results are in essential agreement with free-field studies. VSRFs were found to be shaped by excitatory and inhibitory interactions of activity arriving from the two ears. Some cortical neurons were found to preserve the spectral information in the free-field sound which was generated by the acoustical properties of the head and pinna, filtered by the cochlea and transmitted by auditory nerve fibers.

Acoustic Stimulation↗
PubMed1984

Neural mechanisms of sound localization in an echolocating bat.

The mustache bat emits a three-harmonic echolocation pulse. At the external ear, large interaural intensity differences are generated only when a sound originates within a limited area of two-dimensional space, and this area is different for each pulse harmonic. As a consequence, the external ear generates pronounced binaural spectral cues containing two-dimensional spatial information. This information is encoded in the inferior colliculus by neurons tuned to one of the harmonics and sensitive to interaural intensity differences.

Acoustics↗
PubMed1992

Azimuthal sound localization in the European starling (Sturnus vulgaris): I. Physical binaural cues.

The physical measurements reported here test whether the European starling (Sturnus vulgaris) evaluates the azimuth direction of a sound source with a peripheral auditory system composed of two acoustically coupled pressure-difference receivers (1) or of two decoupled pressure receivers (2). A directional pattern of sound intensity in the free-field was measured at the entrance of the auditory meatus using a probe microphone, and at the tympanum using laser vibrometry. The maximum differences in the sound-pressure level measured with the microphone between various speaker positions and the frontal speaker position were 2.4 dB at 1 and 2 kHz, 7.3 dB at 4 kHz, 9.2 dB at 6 kHz, and 10.9 dB at 8 kHz. The directional amplitude pattern measured by laser vibrometry did not differ from that measured with the microphone. Neither did the directional pattern of travel times to the ear. Measurements of the amplitude and phase transfer function of the starling's interaural pathway using a closed sound system were in accord with the results of the free-field measurements. In conclusion, although some sound transmission via the interaural canal occurred, the present experiments support the hypothesis 2 above that the starling's peripheral auditory system is best described as consisting of two functionally decoupled pressure receivers.

Acoustic Stimulation↗
PubMedDate not supplied

Bilateral amplification and sound localization: then and now.

This article is concerned with the evolution and pros and cons of bilateral amplification. Determining whether a bilateral hearing aid fitting is superior to that of a monaural hearing aid is a long-standing question; for this reason, the trend toward bilateral amplification has been slow. However, it is now assumed that bilateral amplification has significant advantages over monaural amplification in most cases, a view that is supported by our localization results. In this article, we will address the advantages of bilateral hearing aids and reveal some new localization data that show that most listeners with bilateral amplification, when tested unaided, as well as normal-hearing listeners manifested very high degrees of symmetry in their judgments of perceived angle while listeners who routinely use monaural amplification and those with asymmetric hearing loss had relatively large asymmetries. These data show that asymmetry in localization judgments is a much more sensitive indicator of abnormal localization ability than the magnitude of localization errors.

Amplifiers, Electronic↗
PubMed1999

[Hearing loss, disorders of sound localization with the preservation ofsmell and taste in diabetics].

Diabetes is often complicated by serious medical conditions which could be related to the development of auditory system and cranial nerves lesions, disorder of sound localisation and decreased olfactory and taste ability. Cranial nerve palsies in diabetes are considered as an integral part of the main disease. Twenty nine children with diabetes and non-diabetics control group, without a history of exposure to noise, ototoxic drugs, or ear disease aged 4-19 years old were examined. Hearing impairment may be present in children with disease duration above 3-5 years and in children with other complications. Sound localisation tests were performed by the method of Zakrzewski from a free auditory field, measuring the angle of directional hearing acuity in 35 diabetics age from 16 to 78 years. Longer duration of diabetes was associated with higher directional hearing acuity. Higher hearing loss was observed with higher directional values in diabetics. The authors investigated smell and taste in 35 diabetics. All patients were treated with insulin. Impairment value of smell identification thresholds was much more frequent than impairment of smell perception. In no case raised threshold of taste perception.

Adolescent↗