Three factors that promote positive induction when rats respond for 1% sucrose

Studies have demonstrated that rats will increase their operant rate of response for a low-valued reinforcer if a high-valued reinforcer will be available later in the session. Research on this positive induction effect suggests that at least three factors account for its appearance: premature responding for the yet unavailable high-valued reinforcer, an increase in the reinforcing value of the low-valued reinforcer, and responding controlled (e.g., elicited) by the response manipulandum. The present experiment tested whether the size of induction could be systematically altered by varying these factors. Twenty-four rats responded in sessions in which 1% sucrose or a food pellet served as the reinforcer in the first or second half of the session. In some sessions, the same operant response was required in both halves of the session. In others, different responses were required. Half of the rats received the different reinforcers in one food trough while the other half received reinforcers in the different halves of the session in different food troughs. Results demonstrated that a large positive induction effect was observed when all of the above factors were present to contribute to the effect (i.e., high-valued reinforcer upcoming, earned by making the same response, delivered to the same food trough). A small, but significant, induction effect remained when all three were absent (i.e., high-valued reinforcer delivered first, earned by making a different response, delivered to a different food trough). The results support the idea that these three factors are the main contributors to the appearance of this positive induction effect. However, at least one additional factor must also contribute.