Classical Conditioning TodayThe relationship between saliva and a bell root dates back to one of the most studied and well-known cases of learning. Ivan Pavlov was a Russian physician who focused on the study of digestion in the early 1900s. Because he specialized in the breakdown of food, gastric secretion and saliva were important components of his research. Many of his experiments included dogs, which Pavlov noticed salivating whenever meat dust was present. As time went on, he began to recognize that different stimuli also made dogs drool, but in different amounts. Some of these were as simple as a person entering the room or the door opening and closing, signaling that food was arriving. To understand more about the digestive phenomenon, it must also be involuntary. The unconditioned stimulus (US) does not involve any prior learning, but still produces a reaction. It is followed by an unconditioned response (UR) that is inevitably produced by the original stimulus. The conditioned stimulus (CS) is a previously neutral stimulus that ultimately elicits a response after being paired with the unconditioned stimulus. Finally, the conditioned response (CR) is the learned response to the conditioned stimulus once a connection exists between the conditioned and unconditioned stimulus (King, 2014). In Pavlov's experiment, food was the unconditioned stimulus and salivation was the unconditioned response. Over time, the dogs established the connection with the bell, which became a conditioned stimulus. Saliva then became the conditioned response. Although this occurred at the beginning of the 20th century, is Pavlov's dog experiment still relevant today? He found that food is a great example of this. Through different senses, in particular taste and smell, food constitutes an important stimulus. Imagine if one tried a new food and then went to the mall. Hours later they became violently ill. The person eating the food never wants to ingest it again, thinking that it will make them feel nauseous again. This is a form of taste aversion. Even though the food may not be related to the illness, the person has linked it to getting sick. In this case the taste becomes the CS and the aversion the CR; illness and food were the unconditioned stimulus and response respectively (Domjan,