Formulated by Ernst Weber in 1831 to explain the relationship between the physical intensity of a stimulus and the sensory experience that it causes. Weber’s Law states that the increase in a stimulus needed to produce a just-noticeable difference is constant. Later, Gustav Fechner (1801–1887) generalized Weber’s law by proposing that sensation increases as the logarithm of stimulus intensity: S = k logI, where S = subjective experience, I = physical intensity, and k = constant.