Diversity and substitutability of adjunctive activities under fixed-interval schedules of food reinforcement.
Schedule length under fixed-interval reinforcement chooses which collateral behavior you get, and the swap among behaviors is only partial.
01Research in Context
What this study did
Roper (1978) watched lab animals during fixed-interval food schedules. The team set two interval lengths: 30 seconds and 60 seconds. They noted every extra behavior that popped up between pellets.
They also blocked one activity at a time. If they removed the water bottle, they counted whether chewing or wheel-running grew. The goal was to see if these side acts could swap for each other.
What they found
At FI 30-s, animals drank a lot. At FI 60-s, they mostly ran or chewed. The schedule length picked the side behavior.
When the team took away drinking, running rose a little. When they blocked running, drinking rose a little. The swap was weak. The animals did not fully trade one act for another.
How this fits with other research
Johnson et al. (1994) later showed timing matters. They gave water probes at different points inside the same FI. The closer the probe landed to the next pellet, the less the animals drank. This extends J’s work: schedule length sets the behavior, but clock position fine-tunes it.
Davison et al. (1991) added past history. Rats that had lived under long DRL first showed low FI rates even when water was present. Rats with FR history showed high rates. Their data extend J by showing that old contingencies can override the simple 30-s/60-s rule.
Okouchi (2003) also used history, but switched interval lengths between phases. Response rates tracked the prior interval, not the current one. This pattern looks like a contradiction to J’s clean 30-s/60-s split, yet the difference is method: J held one FI per condition, while Hiroto swapped intervals within the same subject. The clash fades when you see J mapped steady-state, Hiroto mapped transition.
Why it matters
For BCBAs, the paper warns that collateral behavior is baked into the schedule, not just the learner. If you run a 30-s FI token board and see constant water-seeking, the schedule may be the culprit, not poor self-control. Before you treat the behavior, try lengthening the interval or giving a different task. Small timing tweaks can shift the whole side-act menu.
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02At a glance
03Original abstract
Six rats received food contingent on pressing a lever on fixed-ratio 1, fixed-interval 30-second, and fixed-interval 60-second schedules, with concurrent access to a drinking spout, a running wheel, and a block of wood. Drinking, running, and chewing were monitored automatically, and these and other activities were observed directly during selected sessions. Because all sessions ended after delivery of 60 pellets, total time available for activities other than eating increased over the three schedules. Time spent contacting the lever and visiting the food tray increased in proportion to total available time, whereas the time spent in other activities changed in a complex manner such that drinking was the dominant adjunctive behavior in the 30-second condition, and running or chewing the dominant adjunctive behavior in five of six rats in the 60-second condition. General activity and grooming also occupied significant amounts of time. In a subsequent part of the experiment, running and chewing were prevented, and the majority of other activities, especially drinking and grooming, increased. The results show that (a) FI schedules of food reinforcement are accompanied by a wide variety of adjunctive activities; (b) the preferred activity differs according to the schedule duration; and (c) the extent to which activities substitute for one another is limited by the tendency for different activities to occupy different parts of the interreinforcement interval.
Journal of the experimental analysis of behavior, 1978 · doi:10.1901/jeab.1978.30-83