jnd, just-noticeable difference - (psychophysics) the difference between two stimuli that (under properly controlled experimental conditions) is detected as often as it is undetected

Fechner's law, Weber-Fechner law - (psychophysics) the concept that the magnitude of a subjective sensation increases proportional to the logarithm of the stimulus intensity; based on early work by E. H. Weber

power law, Stevens' law, Stevens' power law - (psychophysics) the concept that the magnitude of a subjective sensation increases proportional to a power of the stimulus intensity

Weber's law - (psychophysics) the concept that a just-noticeable difference in a stimulus is proportional to the magnitude of the original stimulus; "Weber's law explains why you don't notice your headlights are on in the daytime"

experimental psychology, psychonomics - the branch of psychology that uses experimental methods to study psychological issues