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What is Steven’s Law?

What is Steven’s Law?

Steven’s Law provides a direct method to measure stimulus intensity and sensation. In his method, a series of stimuli are presented to subjects for them to assign numbers proportional to the corresponding subjective impressions. Stevens found that the relation between the scale and physical intensity was not logarithmic. He found that the intensity of a sensation is proportional to stimulus intensity raised to a certain power. S = kITM

When N is smaller than 1, sensation grows more rapidly than stimulus intensity and when N is larger than 1, sensation grows more rapidly than stimulus intensity. Stevens’ model scales the subjective intensity (S) directly and does not use the indirect scaling via JNDs as does Fechner’s model. An experiment using Stevens direct magnitude estimation would ask a subject to assign a number to each standard intensity. For example, each standard intensity would have an assigned number (modulus). The subject would be presented a standard stimulus then a second stimulus. If the second stimulus is twice as loud as the standard, and the standard has an assigned modulus of 10, the subject would give the stimulus a rating of 20.

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