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Context effects in time disrimination. (Re: Boggie Bob)
For the past several years, I have been examining the effect of
rhythmic context changes on listeners ability to compare the tempo
of isochronous tone sequences. In one of these studies, the listeners'
task is to judge whether a comparison interval is faster (shorter),
slower (longer), or the same tempo as an isochronous standard. The
onset of the first tone defining the comparison interval can occur
early, late, or in the rhythm of the standard sequence (as defined by
the fixed IOI of the standard).
Two key factors are worth mentioning here in light of the recent
discussion. First, when measuring temporal resolution it is important
to separate discrimination thresholds for faster and slower
comparison patterns, (and similiarly, for shorter and longer comparison
intervals). In a paper that is to appear in JEP-HPP, Gary Kidd and I
report systematic differences between faster/slower thresholds as
a function of the rhythmic context (early versus late) and the base
tempo. If you would like more information, you can retrieve a pre-print
of this article at http://psy.uq.edu.au/~devin
See also Vos et al, 1997, Psychological Research, 59:240-247 for another
study which examines perceived differences in faster and slower as a
function of base tempo.
The second factor concerns trial-to-trial uncertainty. Work by Watson
and colleagues on frequency discrimination has shown that listeners's
ability to detect frequency changes to a target tone within a rapid tone
sequence depends on whether the same sequence is presented on
each trial (a low uncertainty condition) compared with when the sequence
varies from trial to trial (a high uncertainty condition). Similiarly, we
have shown that within-trial context effects in time-discrimination are
mediated by what temporal pattern the listener expects on each trial.
The effect of an early or late onset on subsequent discriminations tends
to go away if the listener can learn to expect that the comparison
sequence is early or late.
Dr. Devin McAuley
School of Psychology
University of Queensland
Brisbane, QLD 4072
www : http://psy.uq.edu.au/~devin