Pavlov's classic experiments on classical conditioning demonstrated that organisms can learn to associate neutral stimuli with biologically significant stimuli, as when his dogs learned to salivate to a tone that predicted food. Later research expanded on Pavlov's work to show the importance of cognitive processes and biological predispositions in conditioning, and that conditioning principles can help explain diverse phenomena like drug addiction, immune responses, phobias, and advertising effectiveness. Pavlov's work established classical conditioning as a fundamental form of learning and influenced the development of behaviorism.