Due to his industrious studies on classical conditioning, Ivan P. Pavlov (1849–1936) is considered one of the most prominent researchers in psychology. He was born in Ryazan, Russia, a small village where his father was the local priest. Although initially interested in theology and considering following in his father's footsteps, Pavlov was heavily influenced by Charles Darwin's On the Origin of Species , which contributed to his shift in vocation and dedication to the study of science instead of religion. Pavlov studied medicine at the University of Saint Petersburg in Russia, where he received his doctorate in medicine and then traveled to Germany to continue specializing in physiology. During his early work, he focused on the study of the digestive system, which earned him the Nobel Prize in Physiology or Medicine in 1904. During Pavlov's research on the physiology of gastric and salivary glands in dogs, he and his colleagues noticed that secretion of saliva may be induced not only…