Subject: Context effects in time disrimination. (Re: Boggie Bob) From: Devin McAuley <devin(at)psy.uq.edu.au> Date: Thu, 20 Nov 1997 11:56:38 +1000Dear List, 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. Best wishes, Devin ------------------------------------------------------------ Dr. Devin McAuley School of Psychology University of Queensland Brisbane, QLD 4072 Australia email: devin(at)psy.uq.edu.au phone: +61-7-3365-6778 www : http://psy.uq.edu.au/~devin