Gustav Theodor Fechner was a German physicist, philosopher, and experimental psychologist. A pioneer in experimental psychology and founder of psychophysics, he inspired many 20th-century scientists and philosophers. He is also credited with demonstrating the non-linear relationship between psychological sensation and the physical intensity of a stimulus via the formula: , which became known as the Weber–Fechner law.

Experimental psychology refers to work done by those who apply experimental methods to psychological study and the underlying processes. Experimental psychologists employ human participants and animal subjects to study a great many topics, including sensation, perception, memory, cognition, learning, motivation, emotion; developmental processes, social psychology, and the neural substrates of all of these.