Binaural Range Finding from Synthetic Aperture Computation as the Head is Turned

2021

Acoustics

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Wallach (J. Exp. Psychol. 1940, 27, 339–368) predicted that a human subject rotating about a vertical axis through the auditory centre, having an acoustic source rotating around the same axis at twice the rotation rate of the human subject, would perceive the acoustic source to be stationary. His prediction, as confirmed by the experiment, was made to test the hypothesis that humans integrate head movement information that is derived from the vestibular system and visual cues, with measurements of arrival time differences between the acoustic signals received at the ears, to determine directions to acoustic sources. The simulation experiments described here demonstrate that a synthetic aperture calculation performed as the head turns, to determine the direction to an acoustic source (Tamsett, Robotics 2017, 6, 10), is also subject to the Wallach illusion. This constitutes evidence that human audition deploys a synthetic aperture process in which a virtual image of the field of audition is populated as the head turns, and from which directions to acoustic sources are inferred. The process is akin to those in synthetic aperture sonar/radar technologies and to migration in seismic profiler image processing. It could be implemented in a binaural robot localizing acoustic sources from arrival time differences in emulation of an aspect of human audition.

Section: Introductionmentioning

confidence: 99%

The Binaural Illusion of Wallach (1940) Apparent in Synthetic Aperture Images of the Field of Audition Generated as the Head Turns

2021

Acoustics

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“…It has previously been described how acoustic source localisation can be achieved in a binaural system by synthetic-aperture calculation as an image-processing-based operation performed in a virtual acoustic image of the field of audition [2][3][4][5]. This suggestion first arose as a cross-fertilisation from the field of applied geophysics to that of binaural audition [2] in a consideration of how a synthetic-aperture process, familiar to geophysicists as that of "migration" applied in seismic reflection image processing [6], and in synthetic aperture sonar and radar systems [6], may be applied to localise far-field acoustic sources (having an effectively infinite range) to yield visualised solutions to the binaural localisation problem in two-dimensional (2-D) images of the field of audition.…”

Section: Introductionmentioning

confidence: 99%

“…This suggestion first arose as a cross-fertilisation from the field of applied geophysics to that of binaural audition [2] in a consideration of how a synthetic-aperture process, familiar to geophysicists as that of "migration" applied in seismic reflection image processing [6], and in synthetic aperture sonar and radar systems [6], may be applied to localise far-field acoustic sources (having an effectively infinite range) to yield visualised solutions to the binaural localisation problem in two-dimensional (2-D) images of the field of audition. The process was subsequently extended to three dimensions, to not only to find the directions, but also to estimate the ranges to near-field acoustic sources (appropriate for ranges extending to several times the distance between the ears or listening antennae) [3]. In this paper, an exploration is focused on the extent to which a synthetic-aperture approach to binaural localisation can predict the experience of sound apparently emanating from our auditory centre (i.e., an effective zero range) when listening to monophonic sound through headphones.…”

Section: Introductionmentioning

confidence: 99%

“…No matter whether humans or other animals unconsciously perform a synthetic aperture process for sound localisation, it might nevertheless, be applied as an elegant image-processing-based solution to acoustic localisation in a binaural robotic system [2][3][4][5] readily affording a full visualisation of both processing workings and solutions.…”

Section: Introductionmentioning

confidence: 99%

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Binaural Synthetic Aperture Imaging of the Field of Audition as the Head Rotates and Localisation Perception of Monophonic Sound Listened to through Headphones

2021

Acoustics

Self Cite

A human listening to monophonic sound through headphones perceives the sound to emanate from a point inside the head at the auditory centre at effectively zero range. The extent to which this is predicted by synthetic-aperture calculation performed in response to head rotation is explored. The instantaneous angle between the auditory axis and the acoustic source, lambda, for the zero inter-aural time delay imposed by headphones is 90°. The lambda hyperbolic cone simplifies to the auditory median plane, which intersects a spherical surface centred on the auditory centre, along a prime meridian lambda circle. In a two-dimensional (2-D) synthetic-aperture computation, points of intersection of all lambda circles as the head rotates constitute solutions to the directions to acoustic sources. Geometrically, lambda circles cannot intersect at a point representing the auditory centre; nevertheless, 2-D synthetic aperture images for a pure turn of the head and for a pure lateral tilt yield solutions as pairs of points on opposite sides of the head. These can reasonably be interpreted to be perceived at the sums of the position vectors of the pairs of points on the acoustic image, i.e., at the auditory centre. But, a turn of the head on which a fixed lateral tilt of the auditory axis is concomitant (as in species of owl) yields a 2-D synthetic-aperture image without solution. However, extending a 2-D synthetic aperture calculation to a three-dimensional (3-D) calculation will generate a 3-D acoustic image of the field of audition that robustly yields the expected solution.

“…Range can also be estimated from inter-aural level difference (ILD) [21] though the method is appropriate only for ranges that are a small factor of the distance between the listening antennae. Range can in principle be estimated using the synthetic aperture computation approach [22] but also restricted to ranges that are small factor of the distance between the antennae.…”

Section: Introductionmentioning

confidence: 99%

Representation of Multiple Acoustic Sources in a Virtual Image of the Field of Audition from Binaural Synthetic Aperture Processing as the Head is Turned

2018

Robotics

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The representation of multiple acoustic sources in a virtual image of the field of audition based on binaural synthetic-aperture computation (SAC) is described through use of simulated inter-aural time delay (ITD) data. Directions to the acoustic sources may be extracted from the image. ITDs for multiple acoustic sources at an effective instant in time are implied for example by multiple peaks in the coefficients of a short-time base (≈2.25 ms for an antennae separation of 0.15 m) cross correlation function (CCF) of acoustic signals received at the antennae. The CCF coefficients for such peaks at the time delays measured for a given orientation of the head are then distended over lambda circles in a short-time base instantaneous acoustic image of the field of audition. Numerous successive short-time base images of the field of audition generated as the head is turned are integrated into a mid-time base (up to say 0.5 s) acoustic image of the field of audition. This integration as the head turns constitutes a SAC. The intersections of many lambda circles at points in the SAC acoustic image generate maxima in the integrated CCF coefficient values recorded in the image. The positions of the maxima represent the directions to acoustic sources. The locations of acoustic sources so derived provide input for a process managing the long-time base (>10s of seconds) acoustic image of the field of audition representing the robot’s persistent acoustic environmental world view. The virtual images could optionally be displayed on monitors external to the robot to assist system debugging and inspire ongoing development.