Spatial Sound Localization Research Articles

The Role of Asymmetry of the Left and Right External Ear of Bottlenose Dolphin (Tursiops truncatus) in the Spatial Localization of Sound

The Role of Asymmetry of the Left and Right External Ear of Bottlenose Dolphin (Tursiops truncatus) in the Spatial Localization of Sound

The Role of Asymmetry of the Left and Right External Ear of Bottlenose Dolphin (Tursiops truncatus) in the Spatial Localization of Sound

It is generally accepted that Odontoceti lost their external ears (pinnae) in the process of adapting to aquatic habitats. However, their hearing localizes sound with an accuracy of 1° in the frontal and median planes and is directional. These facts indicate the presence of morphological structures functionally performing the role of evolutionarily new external ears adapted to the aquatic environment. The data available to date suggest that this role is played by the left and right row of mental foramens (MFs) and the morphological structures of the rostrum and skull of the dolphin. In this study, for the first time for Odontoceti, the paths of sound travel along MFs and mandibular canals of the lower jaw of bottlenose dolphin (Tursiops truncatus) are measured, and the relative time delays of sound between the MF and the degree of their acoustic shielding by the rostrum and skull depending on the localization of sound in space are calculated. It was established that the left and right outer ear form unique temporal and spectral signs of the spatial localization of sound with a maximal accuracy realized rostrally. Localization mechanisms are based on asymmetry, including rostral–caudal and left–right mutually complementary asymmetry of MF architecture, dorsal–ventral asymmetry in the size of the rostrum, as well as rostral–ventral asymmetry in the position of the left and right row of MFs on the rostrum and rostral–caudal asymmetry in the sizes of the rostrum and skull. Thus, unlike the outer ears of terrestrial animals and human beings limited by the auricles, the outer ears of the dolphin are integrated into the streamlined shape of the rostrum and head of the dolphin, which reduces the resistance to its movement from the water side and, most importantly, does not worsen the signal-to-noise ratio of the flow around it in its hearing with increasing speed. Based on the morphology similarity of Odontoceti, it is natural to assume that their MFs and the morphological structures of the rostrum and skull play the role of external ears and form signs of spatial localization of sounds.

Spatial Localization of Sound in the Late-Blind During Spatial Bisection Task and Minimum Audible Angle Task


 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Objectives
 Our objective was to assess the spatial localization of sound in both minimum audible angle task and spatial bisection task in the azimuthal plane in late blind subjects.
 Methods
 A total of ten late blind individuals and eight normal sighted blindfolded controls performed the spatial bisection task and minimum audible angle task.
 Results and Conclusion
 The late blind performed as good as the controls in both the tasks. The late blind would have had intact vision in their developmental years, enabling development of the ability to spatially localize sound. These results support the cross sensory calibration hypothesis that vision calibrates spatial localization of sound while the sensory system is still maturing.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Spatial Localization of Sound in Early Blind During Spatial Bisection Task and Minimum Audible Angle Task


 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Background
 Research has shown that early blind have supra-normal localization abilities in the azimuthal plane while performing a minimum audible angle task which is based on egocentric paradigm. An opposing view has been proposed that the early blind have a deficit in spatial localization of sound in the horizontal plane during an allocentric based task such as spatial bisection of sound. The objective of our study was to assess spatial localization of sound in the early blind by means of minimum audible angle task and spatial bisection task.
 Methods
 A total of ten early blind and ten normal sighted blind folded controls were subjected to minimum audible angle task and spatial bisection task in the azimuthal plane.
 Results
 The early blind subjects performed significantly poorer than controls in the spatial bisection task which was based on the allocentric model. However, they performed as well as the controls in the Minimum audible angle task which was based on egocentric model.
 Conclusion
 The minimum audible angle task based on the egocentric paradigm does not require a metric representation of auditory space whereas allocentric paradigm based task would require the same. However the spatial bisection task which is based on the allocentric paradigm taxes the retinotopic maps. Hence the poor performance in this task
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Gender Differences in Spatial Localization of Sound in the Azimuthal Plane in Normally Sighted Young Adults


 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Background
 Research studies have shown that there are differences in the neuroanatomy of males and females. The aim of our study was to find whether there are any gender differences in the spatial localization of sound.
 Method
 A total of eighteen blindfolded subjects, consisting of nine males and nine age-matched females with normal hearing, were subjected to the spatial bisection task where they had to localize the second sound, whose location varied from-20° to +20° in the azimuthal plane, while the first and third sound were fixed at-20° and +20° respectively. The Minimum audible angle task was administered, where the subjects had to say whether the 2 sounds presented were from same location or from two different speakers.
 Results and Conclusion
 There was no significant difference between the males and females with respect to their performance of spatial bisection task and minimum audible angle task.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Spatial Localization of Sound in the Late-Blind During Spatial Bisection Task and Minimum Audible Angle Task

Spatial Localization of Sound in the Late-Blind During Spatial Bisection Task and Minimum Audible Angle Task

Spatial Localization of Sound in Early Blind During Spatial Bisection Task and Minimum Audible Angle Task

Spatial Localization of Sound in Early Blind During Spatial Bisection Task and Minimum Audible Angle Task

Gender Differences in Spatial Localization of Sound in the Azimuthal Plane in Normally Sighted Young Adults

Gender Differences in Spatial Localization of Sound in the Azimuthal Plane in Normally Sighted Young Adults

Sound source localization

Sound source localization is paramount for comfort of life, determining the position of a sound source in 3 dimensions: azimuth, height and distance. It is based on 3 types of cue: 2 binaural (interaural time difference and interaural level difference) and 1 monaural spectral cue (head-related transfer function). These are complementary and vary according to the acoustic characteristics of the incident sound. The objective of this report is to update the current state of knowledge on the physical basis of spatial sound localization.

Fast multipole boundary element method to calculate head-related transfer functions for a wide frequency range

Head-related transfer functions (HRTFs) play an important role in spatial sound localization. The boundary element method (BEM) can be applied to calculate HRTFs from non-contact visual scans. Because of high computational complexity, HRTF simulations with BEM for the whole head and pinnae have only been performed for frequencies below 10 kHz. In this study, the fast multipole method (FMM) is coupled with BEM to simulate HRTFs for a wide frequency range. The basic approach of the FMM and its implementation are described. A mesh with over 70 000 elements was used to calculate HRTFs for one subject. With this mesh, the method allowed to calculate HRTFs for frequencies up to 35 kHz. Comparison to acoustically-measured HRTFs has been performed for frequencies up to 16 kHz, showing a good congruence below 7 kHz. Simulations with an additional shoulder mesh improved the congruence in the vertical direction. Reduction in the mesh size by 5% resulted in a substantially-worse representation of spectral cues. The effects of temperature and mesh perturbation were negligible. The FMM appears to be a promising approach for HRTF simulations. Further limitations and potential advantages of the FMM-coupled BEM are discussed.

Application of binaural hearing system for assessment of environmental noise impact

In the present work an experimental system is presented that allows one to investigate physical principles of binaural hearing and identication of sound sources. It is checked that at low frequencies interaural time difference (whereas at high frequencies n the interaural level difference) cue is preferable for recognizing location of sound sources. At intermediate frequencies human auditory system uses both processes for binaural hearing. Also the effect of trafc noise on binaural hearing is investigated. It is shown that environmental noises consist mainly of low frequency spectral components. Therefore noise is considered to have inuence on binaural cues which human auditory system uses for spatial sound localization at low frequencies, i. e. the interaural time difference.

Binaural model for artificial spatial sound localization based on interaural time delays and movements of the interaural axis

This paper presents a mathematical model for sound localization in space using two-microphone devices that possess at least two degrees of freedom. It proves a series of theorems and lemmas that are based on time difference of arrival measurements and movements of the interaural axis, forming a powerful instrument for practical robot applications. For instance, it shows that a single determined rotation of the interaural axis is sufficient to exactly yield the azimuth or the elevation of an immobile sound source in the far field, independently of microphone spacing and the speed of sound and hence of the surrounding medium. It proves that at any moment the knowledge of one value determines the magnitude of the other, with the restriction that the sign of the second value is undefined, which means that, depending on the rotation, either the back-front or the up-down ambiguity is kept unsolved. This paper also shows that parallax motion unlocks essential information about the distance and the Cartesian coordinates of the sound source. Shifting the microphone system sideways fixes the distance and the coordinate on the interaural axis. Combining rotation and translation movements completely solves the localization problem. In order to illustrate the efficacy of the model, this paper presents experiments with a low cost robot developer kit during which the azimuth, the elevation, and the distance of continuous sound sources are determined at a precision of 10 degrees and 0.5 m, respectively. Achieving this performance with low power material demonstrates how easily the model can be implemented into any robotic system.

Neurological development of kittens

The neurological development of the kitten was studied from birth to 120 days of age. Three motor features present at birth disappeared within the 1st 45 days of life. The labyrinthine head and body righting reactions were present at birth; the latter matured only by 25 days of age when the air righting reaction (mature by 35 days) started to appear. Limb placing reactions developed progressively with proprioceptive components being present at birth whereas tactile components evolved slowly from early contact lifting to forepaws contact placing (60 days) and narrow plank walking (75 days). Standing and walking were well developed by 45 days. Eye opening occurred at 9.5 days and several eyeblink reactions (including blink to light) were present at birth. Adequate binocular coordination was seen by 47 days. Vision progressed parallel to the clearing of the ocular media which were fairly transparent by 32 days. Visually guided paw placing and the visuopalpebral blink reflex matured later (by 37 and 59 days, respectively). The external auditory canal and pinna were fully developed by 12 and 31 days, respectively; spontaneous and tactile pinna movements were present at birth; orienting to animal and nonanimal sounds was well developed by 6.5 and 18 days, respectively; spatial sound localization was developed by 16 days and differential responding to animal sounds matured by 24.5 days. Somatic responses and olfaction were present at birth but matured further thereafter. Playful interactions between kittens started by 10--15 days and well developed play behavior was seen by 36--40 days. In brief, all neurological functions mature progressively during the 1st 3 postnatal months.