Schaal, D. W., Odum, A. L., & Shahan, T. A. (2000).
Pigeons may not remember the stimuli that reinforced their recent behavior.
Journal of the Experimental Analysis of Behavior,
73, 125-139.
In two experiments the conditioned reinforcing and delayed
discriminative stimulus functions of stimuli that signal delays
to reinforcement were studied. Pigeons' pecks to a center key
produced delayed-matching-to-sample trials according to a
variable-interval 60-s (or 30-s in 1 pigeon) schedule (Experiment
1) or a multiple variable-interval 20-s variable-interval 120-s
schedule (Experiment 2). The trials consisted of a 2-s
illumination of one of two sample key colors followed across
phases by delays ranging from 0.1 to 27.0 s followed in turn by
the presentation of matching and nonmatching comparison stimuli
on the side keys. Pecks to the key color that matched the sample
were reinforced with 4-s access to grain. Under some conditions
of Experiment 1, pecks to nonmatching comparison stimuli produced
a 4-s blackout and the start of the next interval. Under other
conditions of Experiment 1 and each condition of Experiment 2,
pecks to nonmatching stimuli had no effect and trials ended only
when pigeons pecked the other, matching stimulus and received
food. The functions relating pretrial response rates to delays
differed markedly from those relating matching-to-sample accuracy
to delays. Specifically, response rates remained relatively high
until the longest delays (15.0 to 27.0 s) were arranged, at which
point they fell to low levels. Matching accuracy was high at
short delays, but fell to chance at delays between 3.0 and 9.0 s.
In Experiment 2, both matching accuracy and response rates
remained high over a wider range of delays in the
variable-interval 120-s component relative to the
variable-interval 20-s component. The difference in matching
accuracy between the components was not due to an increased
tendency in the variable-interval 20-s component toward proactive
interference following short intervals. Thus, under these
experimental conditions the conditioned reinforcing and the
delayed discriminative functions of the sample stimulus depended
on the same variables (delay and variable-interval value), but
were nevertheless dissociated.
Key words: delayed matching to sample, conditioned reinforcement,
variable-interval schedules, pigeons, key peck