In the early 1900s, Russian scientist Ivan Pavlov conducted experiments with dogs to study their digestive processes. He noticed that the dogs would salivate not only when food was presented but also when they heard the sound of a bell that had been associated with feeding. This led him to explore the concept of classical conditioning. Pavlov's experiments demonstrated that a neutral stimulus, like a bell, could trigger a response, such as salivation, when paired repeatedly with an unconditioned stimulus, like food. This foundational research has influenced psychology, particularly in understanding how behaviors can be learned through association.