144 Audition
function those circuits and fibers play in hearing. This is per-
haps understandable because most of functional hearing is
based on significant neural computation of the incoming audi-
tory signal. The neural centers that perform the computations
necessary for sound localization, especially computations for
interaural time and level differences, are beginning to be
sorted out, probably because a great deal is known about the
type of computations that are required for accurate sound lo-
calization. Similar work for understanding the functionality of
other auditory neural centers will continue to be an intense
area of interest for auditory science. Progress will require a
better understanding of auditory neural circuits in the central
auditory system, additional knowledge about the auditory
cues used for sound source determination, and testable models
and theories of sound source determination.
Models of auditory processing, especially computational
models, have provided significant new insights into possible
mechanisms of cental auditory processing (Hawkins,
McMullen, Popper, & Fay, 1996). Several computational
models of the auditory periphery have been shown to produce
accurate representations of the spectral-temporal code pro-
vided by the inner ear and auditory nerve. These models can
be used instead of the laborious collection of physiological
data to explore possible models of central mechanisms for
processing sound. Additional work on these models will
continue to be an active area of research in audition.
There is a growing interest in neural imaging (e.g., PET;
positron-emission tomography), especially fMRI (functional
magnetic resonance imaging), as a potentially potent tool for
probing neural mechanisms of auditory processing. Some of
the most recent work is focusing on basic auditory processing
(Griffith, Buchel, Frankowiak, & Patterson, 1998), as opposed
to speech and language processing based on spoken language
(see Fowler chapter in this volume). Such imaging research
will be most useful when the spatial and temporal scales of
measurement allow one to study the individual neural circuits
involved with hearing. New imaging techniques, such as
cardiac triggering and sparse imaging, are just now demon-
strating the promise this technology might provide for better
understanding auditory processing, especially in human
listeners.
Although remarkable progress has been made in under-
standing audition, the field really is in its infancy when one
considers all that is not known. While more is to be learned
about the auditory periphery and the detectability and dis-
criminability of sounds, a major challenge facing audition is
unraveling the function of the central auditory nervous sys-
tem and how it supports our abilities to process the sound
sources that constantly bombard us with crucial information
about the world in which we live.
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