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Re: Ph.D. dissertation available

Brian Karlsen wrote:
> Since Al Bregman would like to see some more dissertation announcements,
> I've
> decided to let you know where you can get a copy of my dissertation.
I think the use of this list for dissertation announcements is a great idea!
A copy of mine is available at http://www.vuw.ac.nz/~trills/thesis
It is 3.5Mb gzipped postscript file.

I've included the abstract below.



The rôle of the bandwidth-duration product WT in the detectability of diotic

Judi Lapsley Miller

8 February 1999

PhD thesis submitted to Victoria University of Wellington, New Zealand.


The bandwidth-duration product WT is a fundamental parameter in most
theories of aural amplitude discrimination of Gaussian noise. These theories
predict that detectability is dependent on WT, but not on the individual
values of bandwidth and duration. Due to the acoustical uncertainty
principle, it is impossible to completely specify an acoustic waveform with
both finite duration and finite bandwidth. An observer must decide how best
to trade-off information in the time domain with information in the
frequency domain. As Licklider (1963) states, "The nature of [the ear's]
solution to the time-frequency problem is, in fact, one of the central
problems in the psychology of hearing." This problem is still unresolved,
primarily due to observer inconsistency in experiments, which degrades
performance making it difficult to compare models. 

The aim is to compare human observers' ability to trade bandwidth and
duration, with simulated and theoretical observers. Human observers
participated in a parametric study where the bandwidth and duration of 500
Hz noise waveforms was systematically varied for the same bandwidth-duration
products (WT=1, 2, and 4, where W varied over 2.5-160 Hz, and T varied over
400-6.25 ms, in octave steps). If observers can trade bandwidth and
duration, detectability should be constant for the same WT. The observers
replicated the experiments six times so that group operating characteristic
(GOC) analysis could be used to reduce the effects of their inconsistent
decision making. Asymptotic errorless performance was estimated by
extrapolating results from the GOC analysis, as a function of replications

Three simulated ideal observers: the energy, envelope, and full-linear
(band-pass filter, full-wave rectifier, and true integrator) detectors were
compared with each other, with mathematical theory and with human observers.
Asymptotic detectability relative to the full-linear detector indicates that
human observers best detect signals with a bandwidth of 40-80 Hz and a
duration of 50-100 ms, and that other values are traded-off in approximately
concentric ellipses of equal detectability. Human detectability of Gaussian
noise was best modelled by the full-linear detector using a non-optimal
filter. Comparing psychometric functions for this detector with human data
shows many striking similarities, indicating that human observers can
sometimes perform as well as an ideal observer, once their inconsistency is

These results indicate that the human hearing system can trade bandwidth and
duration of signals, but not optimally. This accounts for many of the
disparate estimates of the critical band, rectifier, and temporal
integrator, found in the literature, because (a) the critical band is
adjustable, but has a minimum of 40-50 Hz, (b) the rectifier is linear,
rather than square-law, and (c) the temporal integrator is either true or
leaky with a very long time constant.