EXPOSURE TO CONTEXT MAY CONTRIBUTE TO WITHIN-SESSION CHANGES IN RESPONDING

Rats and pigeons responded on multiple variable interval 30-s variable interval 30-s and multiple variable interval 60-s variable interval 6 0-s schedules. The 60-min sessions began 0, 5, 10: 15 or 30 min after the subject was placed in the experimental enclosure, determined rando mly. Early-session response rates were usually higher and the early-se ssion increases in responding were usually smaller, when the beginning of the session was delayed than when it was immediate. These results show that factors related to reinforcement (e.g. satiation, sensitizat ion-habituation to the reinforcers) do not provide a complete explanat ion for within-session changes in operant responding. Instead, an addi tional factor, possibly arousal or sensitization to the experimental c ontext, also contributes. The results suggest an explanation for the s pontaneous recovery of extinguished behavior. (C) 1998 Elsevier Scienc e B.V. All rights reserved.