Grayson’s dog salivates whenever he hears the refrigerator door open because he is accustomed to receiving food each time anyone opens it. Grayson tries an experiment with his dog. Over the next few days, Grayson does not give his dog any food when he opens the refrigerator door, even though he knows the dog expects it. As a result, the dog stops salivating when the refrigerator door is opened. Grayson’s dog’s behavior best illustrates _____ in classical conditioning.