Response additivity: effects of superimposed free reinforcement on a variable-interval baseline.
Free reinforcement can either boost or cut response rates depending on the learner's species and history.
01Research in Context
What this study did
Researchers gave pigeons and rats the same task. Both species worked on a VI 2-min schedule for food. Then the team added free food every 30 seconds. They watched how the extra food changed the animals' pecking or lever pressing.
The study used single-case designs. Each bird and rat served as its own control. Data came from steady-state performance after many sessions.
What they found
Pigeons pecked faster when free food arrived. Their response rate rose above the VI baseline.
Rats did the opposite. They pressed the lever less when free food showed up. Same schedule, opposite effect.
The results show species matters. Free reinforcement does not act the same in every organism.
How this fits with other research
Dove et al. (1974) found that a bird's past schedule changes its future pattern. Pigeons with fixed-ratio history later showed positively accelerated rates under fixed-time food. This supports the idea that history shapes how extra food affects behavior.
Green et al. (1975) and Van Hemel (1973) both saw local contrast in pigeons under multiple VI schedules. When one component switched to extinction, rates rose in the other. These studies help explain why pigeons increased pecking when free food was added.
Cohen et al. (1993) tested rats and pigeons in multiple schedules with response-independent food. They also found species differences in resistance to change. This 1993 paper acts like a later replication of the 1975 species split.
Rogers-Warren et al. (1976) used fixed-interval instead of VI. They saw response patterns flatten when free food was added. The direction of change matched the rat data, showing schedule type also matters.
Why it matters
When you add extra reinforcers, expect different outcomes for different learners. A child with developmental disability might respond like the pigeons, while a neurotypical peer might respond like the rats. Always pilot with one learner first. Track moment-to-moment rates, not just totals. If rates drop, the free reward may be competing with the task. If rates rise, the extra reward may be energizing the behavior.
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02At a glance
03Original abstract
Three experiments examined the effects of superimposing free reinforcement (Free VI 30-sec) on behavior maintained by a response dependent mult VI 2-min VI 2-min schedule of reinforcement. Experiment I used pigeons as subjects, key pecking as the response, and colors of response key as the stimuli associated with the multiple-schedule components. When free reinforcement was added during only one component (Differential condition) a large and highly significant increase in response rate developed in this component. Adding free reinforcement during both components (Nondifferential condition) produced smaller and far less-consistent effects. An entirely different pattern of results was obtained in two subsequent experiments, where similar procedures and reinforcement conditions were used with rats as subjects and bar pressing as the response. In both Experiments II and III, response rates decreased to the stimulus associated with added free reinforcement in the Differential condition. These findings are interpreted as the result of interactions between behavior maintained by response-reinforcer contingencies and behavior maintained by stimulus-reinforcer contingencies. As such, they support the main assumption of an autoshaping theory of behavioral contrast, that additivity of responding generated by the two kinds of contingency can occur only in situations favorable to autoshaping.
Journal of the experimental analysis of behavior, 1975 · doi:10.1901/jeab.1975.23-177