Central Nervous System
When a dog is given food after a bell and this is repeated several times, he will salivate just on hearing the bell. This is an example of:
Classical conditioning was accidentally discovered by Russian physiologist Ivan Pavlov in the 1900s. During his work on salivation Pavlov used to give his dog some food and measured the amount of saliva the dog produced while eating the meal. After the dog had gone through this procedure a few times, however, he began to salivate even before receiving any food. Pavlov spent the rest of his life studying this basic type of associative learning, which is now called classical conditioning or Pavlovian conditioning.