Answer:
a half second before the food
Step-by-step explanation:
Classical conditioning: In psychology, the classical conditioning theory was proposed by Ivan Pavlov. It is described as a learning process whereby a naturally occurring stimulus is being paired with a neutral stimulus to give rise to a learned response.
In the question above, the experimenter is using the classical conditioning technique to make the dog salivate in response to the light after pairing it with food. Therefore, retrieval occurs the most just after the learning procedure and that is why the dog will learn more when the light is being presented just before the food.