Gustav Theodor Fechner (; ; 19 April 1801 – 18 November 1887) was a German physicist, philosopher, and experimental psychologist. A pioneer in experimental psychology and founder of psychophysics (techniques for measuring the mind), 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.
Early life and scientific career
Fechner was born at Groß Särchen, near Muskau, in Lower Lusatia, where his father, a maternal uncle, and his paternal grandfather were pastors. His mother, Johanna Dorothea Fechner (b. 1774), née Fischer, also came from a religious family. Despite these religious influences, Fechner became an atheist in later life.
Fechner's father, Samuel Traugott Fischer Fechner (1765-1806) was free-thinking in many ways, for example by having his children be vaccinated, teaching them Latin, and being a passionate grower of fruit. He died unexpectedly in 1806, leaving the family destitute. Fechner had an elder brother, Eduard Clemens Fechner (1799-1861) and three younger sisters: Emilie, Clementine, and Mathilde. Fechner and his brother were then raised for a few years by his maternal uncle—the pastor, before being reunited with his mother and sistes in Dresden.
Fechner was educated first at Sorau (now Żary in Western Poland).
In 1817 Fechner studied medicine for six months at the in Dresden and from 1818 at the University of Leipzig, the city in which he spent the rest of his life. He earned his PhD from Leipzig in 1823.
In 1834 he was appointed professor of physics at Leipzig. But in 1839, he injured his eyes in the research on afterimages by gazing at the Sun through colored glasses, while studying the phenomena of color and vision, and, after much suffering, resigned. Subsequently, recovering, he turned to the study of the mind and its relations with the body, giving public lectures on the subjects dealt with in his books. Whilst lying in bed, Fechner had an insight into the relationship between mental sensations and material sensations. This insight proved to be significant in the development of psychology as there was now a quantitative relationship between the mental and physical worlds.
Contributions
Fechner published chemical and physical papers, and translated chemical works by Jean-Baptiste Biot and Louis Jacques Thénard from French. He also wrote several poems and humorous pieces, such as the Vergleichende Anatomie der Engel (1825), written under the pseudonym of "Dr. Mises."
Elemente der Psychophysik
Fechner's epoch-making work was his Elemente der Psychophysik (1860). He started from the monistic thought that bodily facts and conscious facts, though not reducible one to the other, are different sides of one reality. His originality lies in trying to discover an exact mathematical relation between them. The most famous outcome of his inquiries is the law known as Fechner's Law, which may be expressed as follows:
"In order that the intensity of a sensation may increase in arithmetical progression, the stimulus must increase in geometrical progression."
The law has been found to be immensely useful, but to fail for very faint and for very strong sensations. Within its useful range, Fechner's law is that sensation is a logarithmic function of physical intensity. S. S. Stevens pointed out that such a law does not account for the fact that perceived relationships among stimuli (e.g., papers coloured black, dark grey, grey, light grey, and white) are unchanged with changes in overall intensity (i.e., in the level of illumination of the papers). He proposed, in his famous 1961 paper entitled "To Honor Fechner and Repeal His Law", that intensity of stimulation is related to perception via a power-law.
Fechner's general formula for getting at the number of units in any sensation is S = c log R, where S stands for the sensation, R for the stimulus numerically estimated, and c for a constant that must be separately determined by experiment in each particular order of sensibility. Fechner's reasoning has been criticized on the grounds that although stimuli are composite, sensations are not. "Every sensation," says William James, "presents itself as an indivisible unit; and it is quite impossible to read any clear meaning into the notion that they are masses of units combined."