CONTENTS
April 2006
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| Vol 34 No 1 | CONTENTS |
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
News
FASTS
Standards Australia
Meeting Reports
New Products
Diary
Acoustics Australia Information
Australian Acoustical Society Information
Advertisers Index
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.
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.
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.
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.
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.
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.
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.