Acoustics Australia Logo (3032 bytes)

Cover April 2006
Vol 34 No 1


April 2006


Listening to the world around us
Simon Carlile

Plasticity In The Adult Central Auditory System
Dexter R. F. Irvine, James B. Fallon and Marc R. Kamke

Efferent Control of Hearing
Wilhelmina H.A.M. Mulders

Genetic Aspects Of Hearing Loss
Hans-Henrik Dahl, Shehnaaz Manji, Michelle de Silva, Marisel Peverelli and Michael Hildebrand

Mitochondria, cell death, and deafness: Will it be possible to prevent presbyacusis?
James O. Pickles

Functionality of Cochlear Micromechanics – As Elucidated By Upward Spread of Masking And Two Tone Suppression
D. Sen and J. B. Allen

A Review Of Mechanical Evidence for a Servo-loop in the Mammalian Cochlea
Eric L. LePage


More About Automotive Exhaust Noise
A.D. Jones

Future Meetings
Standards Australia
Meeting Reports
New Products
Acoustics Australia Information
Australian Acoustical Society Information
Advertisers Index

Listening to the world around us

Simon Carlile,
School of Medical Sciences, University of Sydney, NSW 2006

Vol. 34, No. 1 pp 5 - 11 (2006)
ABSTRACT: Our perception of auditory space depends on the integration of a number of acoustic cues to the locations of sound sources. The binaural cues to location arise as a consequence ofthe two ears being separated by an acoustically dense head which results in differences in the time of arrival and level of the sound at each ear. The outer ears also filter the sound in a directionally dependent manner providing the spectral cues to a sound's location. Real world listening involves separating out multiple concurrent sound sources and differences in their spatial locations provide a means by which auditory spatial attention can be focused on one sound of interest and other masking sounds are ignored. Recent work has demonstrated that spatial release from masking is more effective when the target and maskers are speech sounds and that this involves both bottom up perceptual processes and top-down cognitive processes. This work indicates that preservation ofthe spatial cues is essential for the effective use of hearing aids implicating both binaural and in-the-ear fitting strategies.

Plasticity In The Adult Central Auditory System

Dexter R. F. Irvine1,2, James B. Fallon2 and Marc R. Kamke3
1 School of Psychology, Psychiatry, and Psychological Medicine,
Faculty of Medicine, Nursing, and Health Sciences, Monash University, VIC 3800, Australia
2 Bionic Ear Institute, 384-388 Albert Street, East Melbourne, VIC 3002, Australia
3 School of Behavioural Science, University of Melbourne, VIC 3010, Australia

Vol. 34, No. 1 pp 13 - 17 (2006)
ABSTRACT: The central auditory system retains into adulthood a remarkable capacity for plastic changes in the response characteristics of single neurons and the functional organization of groups of neurons. The most dramatic examples of this plasticity are provided by changes in frequency selectivity and organization as a consequence of either partial hearing loss or procedures that alter the significance of particular frequencies for the organism. Changes in temporal resolution are also seen as a consequence of altered experience. These forms of plasticity are likely to contribute to the improvements exhibited by cochlear implant users in the post-implantation period.

Efferent Control Of Hearing

Wilhelmina H.A.M. Mulders
The Auditory Laboratory, Discipline of Physiology,
School of Biomedical, Biomolecular and Chemical Sciences,
The University of Western Australia, Crawley WA 6009, Australia.

Vol. 34, No. 1 pp 19 - 24 (2006)
ABSTRACT: The auditory system comprises both ascending (afferent) and descending (efferent) pathways. The efferent pathways, which originate in a variety of higher brain centres, are capable of altering the activity in the afferent pathways. By modulating cochlear neural output and central auditory neural circuits, these efferent pathways could play an important role in key auditory processing such as optimising the detection of acoustic signals of interest in the presence of competing background noises. The present paper focuses on the final limb of the efferent pathways, the olivocochlear system, which projects directly to the cochlea. It will describe its proposed role in normal hearing and show how dysfunction of this efferent system could contribute to generation of tinnitus and to deterioration in the detection and processing of signals such as speech, especially in non-optimum listening environments.

Genetic Aspects Of Hearing Loss

Hans-Henrik Dahl, Shehnaaz Manji, Michelle de Silva, Marisel Peverelli, Michael Hildebrand.
Genetic Hearing Research,
Murdoch Childrens Research Institute, The Royal Children's Hospital Parkville, Vic. 3052

Vol. 34, No. 1 pp 25 - 29 (2006)
ABSTRACT: Genes mediate the workings of cells, organs and organisms. Since normal hearing is dependent on highly specialised structures and cellular functions it is not surprising that many genes - as well as environmental factors - affect this complex process. A number of genes have been identified to date that have added to our knowledge of the molecular aspects of hearing. Mutations, or changes, in these genes cause deafness or hearing impairment demonstrating that these genes are essential for normal hearing function. Despite the advances we have made in the discovery of "deafness" genes, little is known about the genes that determine susceptibility to noise-induced deafness, ototoxic hearing loss or early onset presbyacusis. Increasing our knowledge of the genetic aspects of hearing loss will lead to improved genetic counselling and will help the development of novel cell-based, gene or drug therapies.

Mitochondria, Cell Death, And Deafness: Will It Be Possible To Prevent Presbyacusis?

James O. Pickles
Vision, Touch and Hearing Research Centre
School of Biomedical Sciences, University of Queensland
St. Lucia, 4072 Queensland, Australia

Vol. 34, No. 1 pp 31 - 36 (2006)
ABSTRACT: Mitochondria are energy-producing structures within cells, using oxidation to produce the energy-rich compound ATP (adenosine triphosphate) which drives the cell's energy-consuming reactions. Mitochondria are also triggers of programmed cell death, called apoptosis. These two important aspects of cell function are linked: when energy production by the mitochondria fails, a set of biochemical reactions are initiated which lead to destruction of the cell. Some cells types are particularly vulnerable, including certain cells of the inner ear (e.g. outer hair cells and cells of the stria vascularis), leading to sensorineural deafness. It is argued here that this response may be an evolutionary maladaptation, that cell death may be sometimes be triggered unnecessarily, and therefore that some forms of sensorineural hearing loss such as that arising in old age might be preventable.

Fuctionality Of Cochlear Micromechanics - As Elucidated By Upward Spread Of Masking And Two Tone Suppression

D. Sen
School of Electrical Engineering,
The University of New South Wales,
Sydney-UNSW, NSW 2052, Australia.

J. B. Allen
Electrical & Computer Engineering,
University of Illinois at Urbana Champaign,
Urbana, IL 61801, USA

Vol. 34, No. 1 pp 37 - 42 (2006)
ABSTRACT: The effect of increasing the level of a low frequency masker on higher frequency probes can be observed in three paradigms: psychophysically (termed Upward Spread of Masking or USM), mechanically on the basilar membrane (Basilar Membrane Two Tone Suppression or BM2TS) as well as neuro-physiologically at the auditory neurons (Neural Two Tone Suppression or Neural-2TS). This paper reviews various experimental USM, Neural-2TS and BM-2TS data with the aim of shedding light into the underlying physiological mechanisms in the cochlea.

A Review Of Mechanical Evidence For A Servo-Loop In The Mammalian Cochlea

Eric L. LePage
OAEric1e Laboratory, Sydney, Australia
PO Box 6025 Narraweena, 2099

Vol. 34, No. 1 pp 43 - 51 (2006)
ABSTRACT: The outer hair cells in the cochlea are recognised as the active mechanical elements in the normal operation of the cochlear amplifier. Yet the functions of their two motor mechanisms are still not clear. Increasingly, the outer hair cells are also being implicated the control elements in homeostasis - normal regulation of cochlear activity by the descending neural pathway. This review targets articles with mechanical data and suggests new clues as to structure and function in terms of a mechanical-feedback loop for dc-stabilisation. The literature relevant to such an idea is reviewed and directly leads to clues underlying the notion of a time-intensity trade-off for noise exposure, the cause of Meniere's disease and the upward spread of masking.