FECHNER’S LAW

Gustav T. Fechner (1801–1887), professor of physics at the University of Leipzig, sought to measure the mind quantitatively. In approaching this task he studied stimuli and the sensations they aroused. His interest was in ascertaining how sensations changed with changing stimulation. While lying in bed on the morning of October 22, 1850, he conceived the essential idea of what was later to be called Fechner’s law.

Although Weber has given us the theory of JND for the perception of stimuli, which are the basis of the further researches in psychophysics, originally Gustav Fechner first studied the relationship between incoming physical stimuli and the responses to them.

Fechner, with a number of assumptions, generalised Weber’s findings which indicated a broader relationship between sensory and physical intensity. Fechner’s law stated that the strength of a sensation grows as the logarithm of stimulus intensity. The formula is

S = K log I
Where S is psychological (i.e. subjective)
Magnitude
I is stimulus intensity
K is constant

Fechner’s law makes good biological sense as our nervous system compress the huge range of sensation awareness into some manageable scope and this is what a logarithmic transformation does for us.

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