Khallad, Y., & Moore, J. (1996).
Blocking, unblocking, and overexpectation in autoshaping with pigeons.
Journal of the Experimental Analysis of Behavior,
65, 575-591.
Three experiments used pigeons in an autoshaping procedure and a
single-subject design to examine compound stimulus control in
classical conditioning. Experiment 1 examined the blocking
effect, and Experiment 2 examined the unblocking effect. In both
experiments, response-independent food was first delivered
intermittently in the presence of one distinctively colored
houselight but not another. Then, conventional autoshaping trials
were carried out in the presence of each houselight. In
Experiment 1, the keylight readily elicited responding in the
presence of the houselight that had been negatively correlated
with food, but not in the presence of the houselight that had
been positively correlated with food. In Experiment 2, the
keylight readily elicited responding in the presence of the
houselight positively correlated with food, but only when the
amount of food used on the autoshaping trials was either greater
or less than that previously delivered in the presence of the
houselight. Experiment 3 examined the overexpectation effect.
Conventional autoshaping trials were first carried out by
presenting each of two keylights individually. Then, additional
autoshaping trials were carried out by presenting the two
keylights as a compound, with either the same amount of food or a
greater amount of food per trial. Finally, the keylights were
retested by again presenting them individually. The number of
responses per trial elicited by the keylights decreased when the
amount of food used in compound trials was the same as that used
in individual trials. However, the number of responses per trial
remained approximately the same when the amount of food used in
compound trials was greater than that used in individual trials.
Taken together, the results of the three experiments demonstrate
(a) the generality of the blocking, unblocking, and
overexpectation effects by virtue of their extension to
appetitive unconditioned stimuli; (b) the suitability of pigeons
as subjects and autoshaping as a procedure for studying classical
conditioning; and (c) the appropriateness of single-subject
designs.
Key words: blocking, unblocking, overexpectation,
Rescorla-Wagner model, autoshaping, key peck, pigeons