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Examining non-reinforced lever pressing as intrinsically-motivated behavior
Sara R Bond1, Jordan Nerz1, Katie Cagney1
1Department of Psychology, Texas Christian University, 2800 S. University Dr, Box 298920, Fort Worth, TX, 76129, Attn, USA.
Animal Cognition
|June 3, 2026
Summary
The overjustification hypothesis suggests rewards decrease intrinsic motivation. Studies in rats found no evidence for this effect, challenging predictions of behavior change in animals.
Area of Science:
- Behavioral Psychology
- Animal Cognition
Background:
- The overjustification hypothesis posits that external rewards can diminish intrinsically motivated behaviors.
- While studied in humans, its application to animal behavior remains under-explored.
Purpose of the Study:
- To investigate the overjustification effect in rats.
- To determine if providing expected or unexpected reinforcers impacts intrinsically motivated lever pressing behavior.
Main Methods:
- Two experiments were conducted with rats performing lever presses.
- Experiment 1 involved baseline, reinforcement (expected, unexpected, or none), and final baseline periods.
- Experiment 2 modified lever pressing to increase behavioral rates and examined reinforcement effects.
Main Results:
- No evidence for the overjustification effect was found in Experiment 1; lever pressing returned to baseline.
- In Experiment 2, unexpected reinforcement led to higher lever pressing than expected, but not significantly different from no reinforcement.
Conclusions:
- The overjustification effect was not consistently observed in rats, indicating challenges in predicting intrinsic motivation.
- Additional factors likely influence intrinsically motivated behaviors in both human and non-human animals.
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