# Stevens' Power Law Stevens' Power Law (1950s) states that sensation is a power function of stimulus intensity: S = k·I^n. Unlike Fechner's logarithmic law, the exponent n varies by modality—brightness is compressive (n=0.33), electric shock is expansive (n=3.5), line length is linear (n=1.0). S.S. Stevens developed this using magnitude estimation: asking subjects to assign numbers to sensations. The power law better fits experimental data than Fechner's Law and has practical applications in display calibration, audio engineering, and pain measurement. It's part of [[Psychophysics]]—the quantitative study of stimulus-sensation relationships begun by [[Gustav Fechner]] and [[Weber's Law]]. ## Exponents by Modality | Modality | Exponent | Shape | |----------|----------|-------| | Brightness | 0.33 | Compressive | | Loudness | 0.6 | Compressive | | Line length | 1.0 | Linear | | Electric shock | 3.5 | Expansive | ## References - Stevens, S.S. *Psychophysics* (1975) ## Related - [[Psychophysics]] - [[Weber's Law]] - [[Gustav Fechner]] - [[Perception]]