Dougherty, D. H., & Wixted, J. T. (1996).
Detecting a nonevent: Delayed presence-versus-absence discrimination in pigeons.
Journal of the Experimental Analysis of Behavior,
65, 81-92.
Eight pigeons were trained on a delayed presence-versus-absence
discrimination paradigm in which a sample stimulus was presented
on some trials but not on others. If a sample was presented, then
a response to one choice key produced food. If no sample was
presented, a response to the other choice key produced food. The
basic finding was that performance remained constant and well
above 50% correct on no-sample trials as the retention interval
increased, whereas performance dropped precipitously (to below
50% correct) on sample trials. In the second phase of the
experiment, all of the trials were no-sample trials, and
reinforcers were delivered probabilistically for one group of
pigeons and according to time-based schedules for the other
group. The exact reinforcement probabilities used in Phase 2 were
those calculated to be in effect on no-sample trials in Phase 1
(according to a discrete-state model of performance). Subjects
did not show exclusive preference for the richer alternative on
no-sample trials in the first phase, but those in the
probabilistic group developed near-exclusive preference for the
richer alternative during the second phase. These data are
inconsistent with the predictions of the discrete-state model,
but are easily accommodated by an account based on signal
detection theory, which also can be applied effectively to
discrimination of event duration and the "subjective
shortening" effect.
Key words: memory, presence-versus-absence discrimination,
delayed matching to sample, signal detection theory, timing, key
peck, pigeons