Overexpectation in the context of reward timing

• We tested whether the overexpectation (OX) effect exhibited temporal properties.
• Experiment 1 demonstrated a timed OX deficit using traditional delayed conditioning.
• Experiment 2 indicated different functions of response decrement for two timing groups.
• The OX effect was sensitive to when during a stimulus the OX prediction error occurred.

One of the many effects predicted by the Rescorla–Wagner model is overexpectation (OX). The OX effect is the finding that following compound training with two asymptotic elements, X and A, animals emit less conditioned responding (CR, e.g., nose poking) during tests of X alone compared to animals that did not receive compound training. We investigated the OX effect in the context of reward timing by training rats to expect sucrose at different times during X and recording the CR throughout the duration of X. Experiment 1 examined the OX effect using a traditional delayed conditioning procedure. In Experiment 2, the period during which sucrose was expected occurred either early or late during X. Tests revealed that less CR occurred in the OX group around the period that sucrose was previously overexpected, and was otherwise similar in response functions to the control group that did not receive the compound manipulation. These are the first studies pitting the effects of OX with an animal's ability to time their expectation of food.