Re-Evaluation of Weber's Law for Pure Tones

The fact that Weber's law appears to apply in the same way both to intensity discrimination for pure tones and to intensity discrimination for white noise poses a theoretical paradox: in the case of pure tones, the human observer becomes less efficient as the intensity of the tone is increased, while in the case of white noise he exhibits a constant efficiency independent of intensity. At the May, 1957, meeting the author reported experiments conducted with pure tones in noise background suggesting that efficiency is constant rather than decreasing. New data show that with lower noise levels efficiency decreases although not as fast as Weber's law would suggest. The hypothesis that a random amplitude variation in the audio oscillator could lead to these results was tested and found tenable. Physical measurements are illustrated demonstrating the existence of noise of the required order of magnitude (50 db below the oscillator output). The argument is then extended to experiments done in “quiet.” Amplitude variation of oscillators, which is narrow band noise around the frequency of the signal, is sufficient to be consistent with the hypothesis that Weber's law for pure tones can be the result of a property of apparatus rather than a property of the hearing mechanism. (This work was carried out under sponsorship of Evans Signal Laboratory, Signal Corps Engineering Laboratories, Fort Monmouth, New Jersey.)