In psychophysics, the proposition that the magnitude of a sensation is proportional to the logarithm of the intensity of the stimulus causing it, usually expressed by the equation Ψ = k log φ, where Ψ is the magnitude of the sensation, φ is the physical intensity of the stimulus, and k is a constant scaling factor that varies from one kind of sensation to another. It has been largely supplanted by a power law, which Fechner's law approximates for many sensory modalities. Also called the Weber-Fechner law, Fechner himself having called it Weber's law. See also psychophysical function. [Named after the German philosopher, physician, psychologist, and mystic Gustav Theodor Fechner (1801–87) to whom it came as a revelation as he lay in bed on 22 October 1850 contemplating the mind-body problem, although its influence was felt mainly after the publication of his Elemente der Psychophysik in 1860]
Subjects: Psychology — Medicine and Health.