Everyone is familiar with the experiment carried out near the turn of the 19th century by Ivan Pavlov, the Russian physiologist. It’s become synonymous with conditioning, or an involuntary response to a stimulus. Pavlov fed dogs and measured their salivation. He repeated this time after time, and observed that the sounds that preceded the food distribution began themselves to cause the dogs to salivate. That happened even when the bell he rang wasn’t followed by food.