AUDITORY NEUROSCIENCE LABORATORY

Simon Carlile

Simon Carlile took up an appointment as a fixed-term Lecturer in Oct 1993 and begun work on establishing a new auditory laboratory in room 348 of the Anderson Stuart Building. A range of bioacoustic, neurophysiological and psychophysical investigations will be carried out into how the auditory system determines the spatial location of the source of a sound.

RESEARCH in 1993

When one listens to sounds presented via 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'. The laboratory set out to examine the accuracy of localization of sound sources presented in virtual auditory space and began an evaluation of what component(s) of the transformation of the outer ear give rise to the perception of an externalized sound.

RESEARCH PLANNED for 1994

The principal question to be addressed by the work carried out in this laboratory is how the auditory system encodes the spatial location of a sound source. A central methodological theme is the combination of psychophysical investigations using human subjects to determine general perceptual principles combined with neurophysiological investigation of possible mechanisms in a number of animal models.

Psychophysics

The two main objectives of this work are: (i) To determine the acoustical basis of the illusion of virtual auditory space. Current simulations of auditory space vary in their fidelity between listeners. This research will uncover the acoustical basis of these individual differences and allow the realization of a more generalized simulation. (ii) To use this simulation to study the monaural and binaural contributions to the perception of auditory motion.

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 sound's source can only be obtained if information at the two ears is integrated across frequency. The general aim of this work is to determine the sites where this neural integration occurs and to examine the rules by which information converges from a tonotopic (frequency) representation to topographic spatial representation.

PERSONNEL in 1993 and 1994

Dr Simon Carlile 	Lecturer (in-charge)	University	Oct 1993-
Dr Daniele Pralong	Postdoctoral Fellow	ARC		Sep 1994-
Daniel Wardman		BSc(Hons) student			Jan 1994-
Current effective full time personnel =2.0

COLLABORATIONS

The representation of the spatial location of a broad-band sound source in the cortex: Dr Janine Clarey and Dr Mike Calford, Vision, Touch & Hearing Research Centre, Univ. of Queensland (from 1994).

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, Australian National Univ. (from 1994).

FACILITIES

The laboratory occupies rooms 349C and 349D in the Anderson Stuart Building and Simon Carlile's office is room 349A. A 64 cubic metre anechoic chamber is under construction in the Auditory Laboratory (150 Hz cut-off), 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 486 PCs running MacLab and other dedicated analytical software.

FUNDING IN 1994

NHMRC 	Monaural and binaural		Carlile S	1994	$51,973
	processing of spectrally 			1995
	complex sounds					1996

ARC	The acoustical basis of a  	Carlile S	1994	$40,000
	generalized simulation 				1995
	of auditory space				1996

UEG	Anechoic chamber		Carlile S	1994	$52,000

URG	Anechoic chamber for psycho-	Carlile S	1994	$15,000
	physical and physiological
	examination of auditory
	localization
Total for 1994: $158,973

5-YEAR RESEARCH PUBLICATIONS

(The following arose from work at the University of Oxford prior to appointment)

JOURNAL ARTICLES

1990

Carlile S (1990). The auditory periphery of the ferret I: Directional response properties and the pattern of interaural level differences. Journal of the Acoustical Society of America, 88, 2180-2195

Carlile S (1990) The auditory periphery of the ferret II: The spectral transformations of the external ear and their implications for sound localization. Journal of the Acoustical Society of America,88, 2196-2204

1991

Carlile S (1991) The auditory periphery of the ferret: Postnatal development of acoustic properties. Hearing Research, 51, 265-278

1992

Carlile S, Paterson DJ (1992) The effects of chronic hypoxia on human auditory system sensitivity. Aviation Space and Environmental Medicine, 63, 1093-1097

Carlile S, Bascom DA, Paterson DJ (1992) The effect of acute hypoxia on the latency of the human auditory brainstem evoked potential. Acta Otolarangology, 112, 939-945

1993

King AJ, Carlile S (1993) Changes induced in the representation of auditory space in the superior colliculus be rearing ferrets with binocular eyelid suture. Experimental Brain Research, 94, 444-455

Carlile S, King AJ (1993) From outer ear to virtual space. Current Biology, 3, 446-448

Early 1994

Carlile S, King AJ (1994) Monaural and binaural spectrum level cues in the ferret: Acoustics and the neural representation of space. Journal of Neurophysiology, 71, 785-801

Pralong D, Carlile S (1994) Measuring the human head-related transfer functions: construction and calibration of a miniature "in ear" recording system. Journal of the Acoustical Society of America (in press)

Carlile S, Pralong D (1994) The location dependent nature of perceptually salient features of the human head-related transfer functions. Journal of the Acoustical Society of America (in press)

CHAPTER IN BOOK

King AJ, Carlile S (1994) Neural coding for auditory space. The Cognitive Neurosciences, Gazzaniga MS, ed, MIT Press, Boston (in press)