Gustav Fechner

Gustav Fechner (1801–1887) was a German philosopher and experimental psychologist who founded psychophysics, the quantitative study of relationships between physical stimuli and sensation.

Psychophysics: The quantitative study of relationships between physical stimuli and psychological experiences. Fechner gave this field its name and a systematic experimental foundation.
Fechner's law: A psychophysical law stating that sensation grows in proportion to the logarithm of stimulus intensity. This is the quantitative relation most closely associated with Fechner’s name.
Ernst Heinrich Weber: A German physiologist whose experiments on touch and sensory discrimination helped establish quantitative psychophysics. Weber’s findings supplied the empirical relation Fechner later generalized.
Experimental psychology: The scientific study of psychological processes using controlled experiments. Fechner’s measurements helped show that mental phenomena could be studied experimentally.
Weber's law: A principle stating that the smallest detectable change in a stimulus is proportional to its initial intensity. Fechner built his quantitative account of sensation on this relationship.
Weber fraction: The ratio between a just-noticeable stimulus change and the stimulus’s initial intensity. A roughly constant fraction lets successive detectable changes serve as units.
Gottfried Wilhelm Leibniz: A German philosopher and mathematician who proposed that minute perceptions combine into conscious experience. Leibniz’s account of unnoticed perceptions influenced Fechner’s thinking about sensation.
Psychometric function: A function describing how the probability of a response changes with stimulus intensity. Modern threshold research extends the quantitative approach Fechner pioneered.
Just-noticeable difference: The smallest change in a stimulus that can be reliably detected under specified conditions. Fechner treated detectable differences as measurable steps in sensation.
Method of limits: A psychophysical procedure that finds a sensory threshold by gradually increasing or decreasing stimulus intensity. Fechner used threshold procedures to measure perceptual differences.

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