Psychophysics is a very old discipline and, to some extent, it is even older than psychology itself. The origin of psychophysics dates back to 1860, with the publication of a book by Gustav Fechner entitled Elemente der Psychophysik. Interested in the link between the physical reality and the psychological experience we make of it, Fechner proposed in this book different methods for studying this link and the properties of the sensory systems in a scientific way. In fact, during the nineteenth century, the physiology of sensory systems was a very important scientific avenue.