Three experiments examined the assertion that presession handling cues that accompany training with reinforcement might account for spontaneous recovery when they reoccur following extinction. In Experiment 1, after extensive training on a variable-interval schedule, key pecking in pigeons was extinguished following either normal or distinctively different handling and transportational cues. Those cues resulted in enhanced spontaneous recovery 24 hr later when normal cues were reinstated. In Experiment 2, however, subjects tested following the normal handling cues showed no more spontaneous recovery than did subjects that spent the entire extinction-test interval in the experimental chambers and thus were tested without handling cues altogether. In Experiment 3, a group whose test for recovery began 10 min after being placed in the chambers yielded as much spontaneous recovery as did a group tested normally. Furthermore, a group for which extinction began at mid-session and for which handling therefore could not be a discriminative cue for extinction showed no more spontaneous recovery than did the other two groups. Handling cues thus contributed to spontaneous recovery only after explicit discrimination training, as provided in Experiment 1.

In Experiment 1 (within subjects) and Experiment 2 (between subjects) it was shown that the sequential training of pigeons on a color discrimination and then on its reversal, each in a different floor-tilt/ texture context, failed to produce conditional control of discriminative performance by those contexts. Daily alternation between the two problems (with correlated contexts) was successful, however. In each of these experiments conditional control was better reflected in generalization test performance in extinction than during sessions of training with reinforcement.Key words: conditional discrimination, sequential training, key peck, pigeonsConsider an experiment with pigeons in which pecking at a key lighted red is reinforced while pecking at a blue one is extinguished. The red light is a discriminative stimulus that "sets the occasion" for the response by indicating the availability of reinforcement. This three-term contingency between stimuli, responses, and outcomes defines discriminative stimulus control from a conceptual or procedural point of view (Skinner, 1938). Behavioral evidence of discriminative stimulus control consists of differential responding to the different key colors. Next, add another stimulus, the houselight in the operant chamber. When the houselight is on, the aforementioned three-term contingency is in force; when the houselight is off, it is not and some other contingency replaces it. As Sidman (1986) pointed out, this constitutes a four-term contingency that provides a conceptual definition of conditional stimulus control. Conditional stimuli are said to control responding indirectly by virtue of the significance that they impart to other stimuli. Cumming and Berryman (1965) proposed that a conditional cue functions as a "selector of discriminations," that is, it provides "instructional control." Behavioral evidence of conditional stimulus control consists of differential discriminative stimulus control in the presence of different conditional stimuli. Now consider another hypothetical experiment. Pigeons are trained to peck a key, by Requests for reprints should be sent to David R. Thomas, Department of Psychology, Campus Box 345, University of Colorado, Boulder, Colorado 80309. reinforcing that response when the houselight is on; the houselight off accompanies extinction. Next, add another stimulus, a colored light on the response key. When the keylight is blue the contingency between the houselight, key pecking, and reinforcement is in force; when the keylight is red, it is not. From this description, it would appear that the houselight is the discriminative stimulus and the key color is the conditional cue which serves to indicate the significance of the houselight. Yet when we described the previous experiment we designated the key colors as discriminative and the houselight cues as conditional. But the two experiments are one and the same! Thus the conceptual definition of conditional stimulus control cannot specify which stimulus plays a conditional and which plays a ...