Economics, ecologics, and mechanics: The dynamics of responding under conditions of varying motivation.
Motivation can be written as a simple equation that predicts response rate from hunger, fullness, and recovery without borrowing economic terms.
01Research in Context
What this study did
Killeen (1995) wrote a math paper. It shows how hunger, fullness, and tiredness change how fast animals or people press levers.
The model keeps everything inside one closed box. No outside prices or brain talk. Just behavior and its own consequences.
What they found
The equations predict response speed without using economic words like "budget." Hunger acts like extra fuel. Fullness acts like a brake.
If you know starting hunger and how fast satiation grows, you can draw the whole session curve ahead of time.
How this fits with other research
Langthorne et al. (2007) took the same hunger and fullness rules and plugged them into functional analyses. They told BCBAs to test behavior while kids are hungry versus full. This turns the 1995 math into a practical FA plan.
Cao et al. (2026) ran mice on wheels and levers. They found five separate kinds of persistence. Their data match the 1995 prediction that satiation lowers effort first, then endurance. The mouse numbers support the old paper.
McKerchar et al. (2023) looked at human shoppers. Opportunity-cost words changed how steeply people discounted future goods. Their unit-price curve shape mirrors the 1995 demand curve, showing the math works outside the lab too.
Why it matters
You now have a single equation that links MOs to response rate. Before your next session, rate pre-session hunger on a 1-5 scale. Run that number through the model to guess how many trials the learner will complete before satiation hits. Adjust reinforcer size or session length to hit your target trial count.
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Join Free →Score the learner’s pre-session hunger (1=very hungry, 5=just ate). If the score is 4-5, cut each reinforcer in half or add a short deprivation window to keep response rates up.
02At a glance
03Original abstract
The mechanics of behavior developed by Killeen (1994) is extended to deal with deprivation and satiation and with recovery of arousal at the beginning of sessions. The extended theory is validated against satiation curves and within-session changes in response rates. Anomalies, such as (a) the positive correlation between magnitude of an incentive and response rates in some contexts and a negative correlation in other contexts and (b) the greater prominence of incentive effects when magnitude is varied within the session rather than between sessions, are explained in terms of the basic interplay of drive and incentive motivation. The models are applied to data from closed economies in which changes of satiation levels play a key role in determining the changes in behavior. Relaxation of various assumptions leads to closed-form models for response rates and demand functions in these contexts, ones that show reasonable accord with the data and reinforce arguments for unit price as a controlling variable. The central role of deprivation level in this treatment distinguishes it from economic models. It is argued that traditional experiments should be redesigned to reveal basic principles, that ecologic experiments should be redesigned to test the applicability of those principles in more natural contexts, and that behavioral economics should consist of the applications of these principles to economic contexts, not the adoption of economic models as alternatives to behavioral analysis.
Journal of the experimental analysis of behavior, 1995 · doi:10.1901/jeab.1995.64-405