The impossible dream of Fechner and Stevens.

The idea that there is a single psychophysical function which describes how the human responds to stimulus intensity is rejected. The form of any empirical function depends upon the buried yet arbitrary assumption about how the stimuli are to be measured. Because psychophysical functions have this arbitrary basis, there can be no universal law, and further, no psychophysical function can reveal a general truth about the nervous system. The power law has been inappropriately reified; the descriptive usefulness of the power function has been incorrectly extended, perhaps because simplicity is appealing.