Probability and rate of reinforcement in negative prediction error learning.

Trial-based theories of associative learning propose that learning is sensitive to the probability of reinforcement signaled by a conditioned stimulus (CS). Learning, however, is often sensitive to reinforcement rate rather than probability of reinforcement per trial, suggesting that temporal properties of cues may be more important than trial-based properties. In four experiments, the role of probability of reinforcement per trial was examined in appetitive Pavlovian conditioning in mice under conditions in which reinforcement rate was controlled. Experiments 1 and 2 examined the loss of conditioned responding caused by overexpectation of reinforcement. The probability of reinforcement per trial failed to affect acquisition and summation of conditioned responding and failed to affect overexpectation. It also failed to affect extinction of conditioned responding in Experiments 3 and 4. Experiments 2-4 contained nonreinforced trials in which responding at the offset of the CS could be measured. These probe trials did reveal an effect of probability of reinforcement per trial. Cues associated with 100% reinforcement elicited greater post-CS responding than cues associated with 50% reinforcement. The effect was also evident in summation trials (in Experiment 2) in which two 100% or 50% reinforced cues were presented in compound. The results show that mice learn about rate and probability information, but reinforcement rate determines anticipatory responding during the CS. The probability of reinforcement determines responding at the expected time of reinforcement. Thus, learning occurs continuously over the duration of experience and per episode of experience independent of duration. (PsycInfo Database Record (c) 2025 APA, all rights reserved).