A theory of behavioral contrast.
Behavioral contrast is a tug-of-war between the target response and schedule-induced side behaviors, not a simple change in reinforcer value.
01Research in Context
What this study did
Dixon (2014) built a math model of behavioral contrast. The model says contrast comes from two response classes fighting each other. One class is the target operant, like key pecking. The other class is schedule-induced adjunctive behavior, like wing flapping or water dipping.
The paper puts the fight into equations. It keeps the old idea of reinforcement rate but adds competition. When one response gets stronger, the other gets weaker. This push-pull creates the sudden jumps we call positive or negative contrast.
What they found
The model fits classic contrast curves without using a single “value” shift. It shows that when extinction starts, adjunctive behavior rises and eats time. That drop in time spent on the target response looks like negative contrast.
When rich reinforcement returns, adjunctive behavior drops fast. The target response jumps up, looking like positive contrast. The same equations cover both directions with one mechanism: response competition.
How this fits with other research
Older data make sense under this view. REYNOLDS et al. (1961) saw contrast even with FI and DRL schedules. Their birds could not peck faster, yet rates still rose. Dixon (2014) says the rise came from less adjunctive behavior, not faster pecking.
Dews (1978) thought Pavlovian stimulus-reinforcer links drove local contrast. Dixon (2014) keeps the Pavlovian piece but moves it inside the competition loop. The stimulus still triggers adjunctive responses, yet the final change is about time allocation, not added value.
Killeen (2023) updates the same math family. It keeps the competition core but links it to behavioral momentum. Rich schedules build mass; that mass resists change. The 2023 paper is the successor: same engine, bigger frame.
Why it matters
You can now test for adjunctive behavior instead of guessing about “value.” Watch what the client does when reinforcement thins. If stereotypy or other side behaviors spike, you are seeing the competition live. Reduce those adjunctive responses—give a chew, shorten the interval, or add a competing response—and contrast effects may shrink. This gives you a lever beyond “add more reinforcement.”
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02At a glance
03Original abstract
The reinforcers that maintain target instrumental responses also reinforce other responses that compete with them for expression. This competition, and its imbalance at points of transition between different schedules of reinforcement, causes behavioral contrast. The imbalance is caused by differences in the rates at which different responses come under the control of component stimuli. A model for this theory of behavioral contrast is constructed by expanding the coupling coefficient of MPR (Killeen, 1994). The coupling coefficient gives the degree of association of a reinforcer with the target response (as opposed to other competing responses). Competing responses, often identified as interim or adjunctive or superstitious behavior, are intrinsic to reinforcement schedules, especially interval schedules. In addition to that base-rate of competition, additional competing responses may spill over from the prior component, causing initial contrast; and they may be modulated by conditioned reinforcement or punishment from stimuli associated with subsequent component change, causing terminal contrast. A formalization of these hypotheses employed (a) a hysteresis model of off-target responses giving rise to initial contrast, and (b) a competing traces model of the suppression or enhancement of ongoing competitive responses by signals of following-schedule transition. The theory was applied to transient contrast, the following schedule effect, and the component duration effect.
Journal of the experimental analysis of behavior, 2014 · doi:10.1002/jeab.107