AUDITORY NEUROSCIENCE LABORATORY

Simon Carlile

  

  

RESEARCH

PERSONNEL in 1994 and 1995

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.
  

PROJECTS in 1994

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.
  

RESEARCH PLANNED for 1995

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.

Psychophysics

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.

Neurophysiological work

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.
  

COLLABORATIONS

Neural network implementation of a sound localizing system:
Dr Philip Leong, Dept of Electrical Engineering, Univ. of Sydney (1994-present).

Localization in virtual auditory space:
Dr Simon Oldfield and Dr Simon Parker, Human Factors, Air Operations Division, Aeronautical Research Laboratory, Defence Science & Technology Organization, Melbourne (1994-present).

The coding of auditory space in the deep layers of the superior colliculus of the wallaby:
Prof. Richard Mark and Dr Ken Hill, Research School of Biological Sciences, A.N.U. (1994-present).
  

FACILITIES

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.
  

OTHER RESEARCH ACTIVITIES in 1994

Refereeing

Manuscript:
for British Journal of Audiology (1).

Grant application:
for NHMRC (1).

Conference attended

National Acoustics Laboratory three-day workshop on Hearing Research, Sydney (Nov).

Seminar

Dept of Anatomy, Univ. of N.S.W. (Sep).

Service to scientific society

Program Committee, Australian Neural Networks Meeting, Sydney (Feb 95).
  

5-YEAR RESEARCH PUBLICATIONS

Yet to be inserted.

  
MOST RECENT TOTAL ANNUAL CITATIONS (for 1993): 35
   

FUNDING in 1994 and 1995

NHMRC Monaural and Binaural processing of
spectrally complex sounds
Carlile S 1994 $51,973
1995 $27,125

ARC The acoustical basis of a generalized
simulation of auditory space
Carlile S 1994 $40,000
1995 $40,955

US Large Equipment Anechoic chamber Carlile S 1994 $52,000

URG Anechoic chamber for psychophysical
and physiological examination of
auditory localization
Carlile S 1994 $15,000

Total for 1994: $158,973

Total for 1995: $68,060

  

  

TEACHING

COURSES TAUGHT

Medical Science: Human Life Sciences 2

Lectures: 2 new lectures introducing Neuroscience.

Medical Science 3: Neuroscience/Science 3

Lectures: 9 new lectures on sensory processing (auditory, somatosensory and vestibular function).

Practicals: 2 on auditory function.

Tutorials: 1, of 2 h, on revision.

Paper sessions: 4, of 1 h each.

Examination: 1 essay and 8 short answer questions.

Medical Science 3: Advanced Neuroscience

Lectures: 2 new lectures on the topographic representations of sensory space.

Paper session: 5 paper review sessions.

Tutorials: 13 methods and background tutorials on digital signal processing and auditory localization in virtual auditory space for the laboratory based component of the course.

Assessment: Short essay style exam questions.

Pharmacy 1: Neuroscience

Lectures: 3 new lectures on muscle function and 2 new lectures on hearing and balance.

Dentistry 2

Practicals: 1, presented twice, on cutaneous sensation.

Tutorials: 1, presented twice, on cutaneous sensation.
  

TEACHING HOURS in 1994

MedSc 2 MedSc 3 Pharm 1 Dent 2 Total
Lectures 2 11 5

- 18
Practical classes (no.) - 6 (2) -

4 (2) 10
Tutorials - 18 -

2 20
Paper sessions - 18 -

- 18

Total formal contact teaching time = 66 h

Preparing lectures* 20 110 40

1 171
Setting exams 2 1 1

- 4
Marking exams - 6 -

- 6
Marking essays/pracs 6 3 -

- 9
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.
  

  

ADMINISTRATION

(see also OTHER RESEARCH ACTIVITIES in 1994)

Staff development courses

Producing quality teaching (Centre for Teaching and Learning).

Preparing a teaching portfolio and teaching profile (Centre for Teaching and Learning)

7th VC's Forum: Information Technology in Teaching and Learning.

8th VC's Forum: The Library and Information Technology - Present and Future scenarios. (Attended as Faculty representative for the GMP).

Committee membership

Chairman, Computer Based Education (CBE) Committee, Faculty of Medicine.

The responsibilities of this position included:

  1. surveying all teaching departments re current use of CBE,

  2. preparing a 14 page Committee Report for Faculty, and

  3. preparing 12 page funding submission (with A. Sefton) to the Information Technology in Support of Teaching Committee.

These reports have laid the foundations of the model for teaching resource delivery for the entire Graduate Medical Program to be introduced in 1997.

Member, Inter-Departmental Committee for the teaching of Neuroscience in Medicine.