TRANSITIONS FROM RICH-TO-LEAN SCHEDULES INCREASE ATTACK IN A LABORATORY MODEL OF SOCIAL AGGRESSION IN PIGEONS: II. FIXED-INTERVAL SCHEDULES.

Pigeons key pecked under two-component multiple fixed-interval (FI) schedules. Each component provided a different reinforcer magnitude (small or large), signaled by the color of the key light. Attacks toward a live, protected target pigeon were measured. Large- (rich) and small- (lean) reinforcer components alternated irregularly such that four different interval types (transitions) between the size of the immediately preceding reinforcer and the size of the upcoming reinforcer occurred within each session: lean-to-lean, lean-to-rich, rich-to-lean, and rich-torich transitions. The FI for each component was the same within each phase, but was manipulated across phases. For all pigeons, more attack occurred following the presentations of the larger reinforcer (i.e., during rich-to-lean and rich-to-rich transitions). For 2 of the 3 pigeons, this effect was modulated by the size of the upcoming reinforcer; attack following larger reinforcers was elevated when the upcoming reinforcer was small (i.e., during rich-to-lean transitions). This rich-to-lean effect on attack diminished or disappeared as the length of the FI schedule was increased (i.e., control over attack by the upcoming reinforcer size diminished with increases in the inter-reinforcement interval). For all pigeons and at all FIs, however, postreinforcement pauses were longest during the rich-to-lean transitions. These data (1) are consistent with the notion that postreinforcement periods during intermittent schedules function aversively and, thus, can precipitate aggressive behavior, and (2) suggest that rich-to-lean conditions may be especially aversive. They also indicate, however, that aversive effects of rich-to-lean transitions may differ across fixed-ratio (FR) and FI schedules, and that variables controlling attacking and pausing may not be isomorphic between these different schedule types.

Effects of Type of Recall Test and Spaced Presentations of Stimulus Terms, Response Terms and Stimulus-Response Terms on Retention in Paired-Associate Learning

The present experiment tested the effects of reinforcement type (stimulus term, response term, and stimulus-response pairs) and type of recall-retention test (stimulus type or response type) as between- S variables and delay-of-reinforcement interval as a within- S variable on retention in paired-associate learning. The analysis showed that type of reinforcement and delay-of-reinforcement interval resulted in significant effects. Type of recall-retention test was not significant and interactions were nonsignificant.

Effects of Delay of Reinforcement and Cues upon Acquisition and Extinction Performance

The effects of pairing cues with the termination of a delay of reinforcement interval were studied in a discrete-trial barpress situation. In acquisition, one group of rats received immediate reinforcement while a second group received a 10-sec. delay. Light cues were paired with the presentation of reinforcement for both groups. In extinction each group was split and half the Ss received the cues and half the Ss did not. Resistance to extinction, as measured by barpress latency, was reliably greater for the immediate reinforcement and cue conditions. No interaction between delay and cues was evident.

Children's Lever-Pulling Behavior as a Function of Shifts in Delay of Reinforcement Interval: A Modified Replication

A lever-pulling task was used to assess the effects of shifts in delay of reinforcement on children's behavior. Four groups of first grade children served as Ss. Each group experienced one of the four possible factorial combinations of pre-shift (0 vs 9 sec.) and post-shift (0 vs 9 sec.) delay. Results obtained over the pre-shift and transition trials constitute a nearly perfect replication of findings in an earlier experiment (Rieber, 1961b). However, the results obtained over the post-shift trials were inconsistent with those obtained in the earlier study. Possible reasons for the inconsistent findings were discussed, as was a frustration interpretation for shifts in the delay interval. The present post-shift results seem to indicate that Ss who experience delay of reinforcement respond more persistently than Ss who have experienced only immediate reinforcement.