Why can a delay between a response and a food reward interfere with instrumental learning?

In the context of instrumental conditioning, learning is inferred when an animal's behavior changes due to the temporal relationship between a specific response and a subsequent reinforcer, such as food.1

Imposing a delay between the response and the food reward interferes with this process because it disrupts the animal's ability to associate the two events. Even a gap of a few seconds between an action—such as a rat pressing a lever—and the delivery of the reward will seriously hinder the animal's capacity to learn the connection between that behavior and the reinforcement.1

While Ivan Pavlov is primarily associated with classical conditioning, his work established the fundamental importance of temporal relationships in associative learning. In both classical and instrumental experiments, the effectiveness of conditioning relies on the proximity of these events; increasing the interval beyond a certain point invariably causes a decline in the strength of the learned association.1