psychophysical power law

5.49  psychophysical power law; Stevens power law. Description of the relationship between stimulus magnitude and the resulting sensation magnitude. Mathematically,

where Ψ is sensation magnitude, ∅ is stimulus magnitude, ∅0 is the absolute threshold, n is a constant related to a given sense modality, and k is a proportionality constant.

Annotation         The psychophysical power law replaces the Weber-Fechner equation (see 5.64) which held that equal stimulus ratios corresponded to equal sensation differences. The psychophysical power law states that equal stimulus ratios correspond to equal sensation ratios.