W eber's Law

Abstract

Ernst Heinrich Weber (1795–1878), professor of anatomy (1821–1871) and physiology (1840–1866) at the University of Leipzig, on the basis of experiments with stimuli of pressure, lifted weights, and visual distance (line lengths), along with reported observations of others, concluded that, rather than perceiving simply the difference between stimuli being compared, we perceive the ratio of the difference to the magnitude of the stimuli. A similar finding had already been made by the French physicist and mathematician Pierre Bouguer (1698–1758) for visual brightness. Gustav T. Fechner (1801–1887), formerly a student of Weber's and later also a professor at the University of Leipzig, translated this conclusion into the familiar mathematical form used today. Thus Weber's law is usually given as either Δ I/I = k or Δ I = kI, where Δ I is the change required for a just noticeable difference in stimulation (JND), I is the stimulus magnitude, and k is a constant for the particular sense. The value of k is termed the Weber ratio. The equation Δ I = kI shows more clearly the proportional change in stimulation required for a JND. If, for example, the stimulus magnitude is doubled, the amount of change required for a JND is also doubled.