APA Dictionary of Psychology

a psychophysical relationship stating that the psychological magnitude of a sensation is proportional to a power of the stimulus producing it. This can be expressed as Ψ = ksⁿ, where Ψ is the sensation, k is a constant of proportionality, s is the stimulus magnitude, and n is a function of the particular stimulus. Also called Stevens power law. See also Fechner’s law; Weber’s law. [Stanley Smith Stevens]