Mazer, J. E. (1998).
Choice with delayed and probabilistic reinforcers: Effects of prereinforcer and postreinforcer stimuli.
Journal of the Experimental Analysis of Behavior,
70, 253-265.
Experiment 1, pigeons' pecks on a green key led to a 5-s delay
with green houselights, and then food was delivered on 20% (or, in
other conditions, 50%) of the trials. Pecks on a red key led to
an adjusting delay with red houselights, and then food was
delivered on every trial. The adjusting delay was used to
estimate indifference points: delays at which the two
alternatives were chosen about equally often. Varying the
presence or absence of green houselights during the delays that
preceded possible food deliveries had large effects on choice. In
contrast, varying the presence of the green or red houselights in
the intertrial intervals had no effects on choice. In Experiment
2, pecks on the green key led to delays of either 5 s or 30 s with
green houselights, and then food was delivered on 20% of the
trials. Varying the duration of the green houselights on
nonreinforced trials had no effect on choice. The results suggest
that the green houselights served as a conditioned reinforcer at
some times but not at others, depending on whether or not there
was a possibility that a primary reinforcer might be delivered.
Given this interpretation of what constitutes a conditioned
reinforcer, most of the results were consistent with the view that
the strength of a conditioned reinforcer is inversely related to
its duration.
Key words: choice, probability, delay, conditioned
reinforcement, key peck, pigeons.