10.3 Intensity discrimination

The smallest detectable change in intensity has been measured using a variety of psychophysical methods and various stimuli. Although the difference threshold depends on several factors including duration, intensity and the kinds of stimuli on which the measurement is made, Weber's law holds for most stimuli. In other words, the smallest detectable change is a constant fraction of the intensity of the stimulus. Expressed in dB, the minimum change in intensity that produces a perceptual difference is about 0.5 to 1.0dB. However, for pure tones Weber's law does not hold in that discrimination, as measured by the Weber fraction, improves at high levels. For a 1000 Hz tone, the difference threshold ranges from 1.5 dB at 20 dB SPL to 0.3 dB at 80 dB SPL.