|Dr Simon Carlile||Lecturer (in charge)||University||Oct, 1993-|
|Dr Danièle Pralong||Research Associate||ARC||Sep, 1994-|
|Stephanie Hyams||BSc(Hons) student||1995|
|Wing-Yan Chung||ME (0.25) (Supervisor: P. Leong, Elec. Eng.)||1995-|
Current effective full time personnel = 3.25
This Laboratory carries out a range of bioacoustic, neurophysiological and psychophysical investigations into how auditory space is encoded in the nervous system.
Building and installation of an anechoic chamber
A considerable proportion of 1994 was devoted to building a large (64 m3) anechoic chamber in the main auditory laboratory and fitting out this chamber for a range of bioacoustic, psychophysical and neurophysiological investigations. This chamber is anechoic to 150 Hz and has an insertion loss of better than 30 dB for sound frequencies greater than 100 Hz. It is also equipped with a robot arm carrying a small speaker that can be placed at any location on the surface of an imaginary sphere surrounding a test subject located in the middle of the chamber. The stimulus generation system is DSP based and capable of generating arbitrary complex signals with a very high degree of control over time and frequency domain characteristics. Stimulus delivery and data capture is all automated and controlled by a 90 MHz Pentium.
During this year the Laboratory also examined how the spatial separation of competing sounds affects the ability of one sound to mask or obscure the other. When one listens to sounds presented over headphones one normally perceives the source of the sound as coming from a location inside one's head. However, the illusion of a sound source located outside the head can be generated if the sound is first filtered in a manner that mimics the normal filtering of the outer ear. This illusory sound field is commonly referred to 'virtual auditory space' (VAS). Stimuli were presented in VAS using a head-phone delivery system, providing precise control over all of the monaural and binaural cues utilized by the auditory system. Broad band sounds were presented and showed that the unmasking produced by placing the sources of the masker and the target in different locations in space is due to a number of different cues. Firstly, binaural difference in the times of arrival of the sounds at each ear provides the most effective cue, but these only operate when the target is in the low frequency range. Secondly, interaural differences in level which operate for middle to high frequency targets actually produce increased masking, a result contrary to expectations. Finally, there appeared to be a cue that relies upon a comparison of energy level across frequency that operates for signal frequencies in the middle to high frequency range. This last result was also unexpected and probably represents the most significant finding of this study.
In collaboration with Philip Leong (Dept of Electrical Engineering) a study was begun using neural networks to examine the efficacy of localization of information in transformed inputs to the auditory system. These transformations were designed to model the effects of neural encoding of the transfer functions of the outer ear. The medium-term aim of this project is to convert the network to an analyser residing on a VLSI chip to allow the construction of an anthropomorphic robot head that is capable of localizing a sound to the same level of accuracy as a human.
The principal question to be addressed will be how the auditory system encodes the spatial location of a sound source. The intended methodology will incorporate psychophysical investigations using human subjects to determine general perceptual principals, with neurophysiological investigation of possible mechanisms in a number of animal models.
One of the objectives of the psychophysical work will be to determine the acoustical basis of the illusion of VAS. Current simulations of auditory space vary in their fidelity between listeners. The Laboratory's research will be aimed at uncovering the acoustical basis of these individual differences to allow the realization of a more generalized simulation. Work is also planned using VAS to study the monaural and binaural contributions to our perception of auditory motion. In addition, stimuli presented in VAS will be used to examine the mechanisms by which we are able to discriminate a sound of interest against a noisy background.
The neural representation of auditory space is a computational one based on the acoustic cues at each ear. Unlike the visual or somatosensory systems, the auditory sensory epithelia codes frequency rather than space. Unambiguous cues to the location of a sounds source can only be obtained if information at the two ears is integrated across frequency. Thus a further aim will be to determine the sites where this neural integration occurs and examine the rules by which information converges from a tonotopic (frequency) representation to topographic spatial representation.
The Laboratory occupies rooms 349 and 270 in the Anderson Stuart Building. Simon Carlile's office is room 349(a). The main laboratory includes a 64 cubic metre anechoic chamber, together with a remote stimulus positioning system. Supporting equipment includes two digital stimulus systems each capable of stereo delivery of complex spectral signals, a three-space tracking system for monitoring head position, a full neurophysiological recording setup for dual channel extracellular recordings including waveform capture and spike sorting. Equipment for small animal surgery and life support. Networked computational support using fast i486 and Pentium PCs running MacLab and other dedicated analytical software.
Yet to be inserted.
MOST RECENT TOTAL ANNUAL CITATIONS (for 1993): 35
|NHMRC||Monaural and Binaural processing of
spectrally complex sounds
|ARC|| The acoustical basis of a generalized
simulation of auditory space
|US Large Equipment||Anechoic chamber||Carlile S||1994||$52,000|
|URG||Anechoic chamber for psychophysical
and physiological examination of
Total for 1994: $158,973
Total for 1995: $68,060
|MedSc 2||MedSc 3||Pharm 1||Dent 2||Total|
|Practical classes (no.)||-||6||(2)||-||4||(2)||10|
|Total formal contact teaching time = 66 h|
|Marking honours thesis||21|
|Preparation, distribution, analysis and reporting of the Departmental Student Destination review||40|
Other teaching-related time = 251 h
Total time = 317 h
* Time spent preparing lectures was estimated as an average of 10 hours per new lecture and 7 hours where some of the same material was presented in a different format to different students.
(see also OTHER RESEARCH ACTIVITIES in 1994)