Answer:
In trace conditioning, the conditioned stimulus (CS) begins and ends before the unconditioned stimulus (US) appears.
To understand this concept, it's important to first understand the basics of classical conditioning, a type of associative learning that was first demonstrated by Ivan Pavlov, a Russian physiologist. In his famous experiments with dogs, Pavlov showed that a neutral stimulus (like a bell), when paired with an unconditioned stimulus (like food) that naturally and automatically triggers a salivating response, can eventually come to trigger that same response even when presented alone. This is known as a conditioned response.
In classical conditioning, there are several types of procedures or paradigms, including forward conditioning, simultaneous conditioning, backward conditioning, and trace conditioning. The difference between these paradigms lies in the timing and order of the presentation of the CS and US.
In trace conditioning, the CS is presented and then removed, and after a short "trace" interval, the US is presented. For example, if you ring a bell (CS), wait for a few seconds (trace interval), and then present food to a dog (US), over time the dog will begin to salivate at the sound of the bell alone. The dog has learned to associate the bell with the food, even though there is a time gap or "trace" between them.