Introduction

It is interesting to find this old definition in one of the world's most prestigious dictionaries of the English language, the Oxford Shorter Dictionary in two volumes “based on historical principles.” Who today writes of “psychic action,” and who would gather that the word emerged in Fechner's 1860 book Elemente der Psychophysik (translated by Adler in 1966)?

To know what actually was intended and what has become the activity of psychophysics, we must both go back in time and then return to the present. Although it is common to write of stimulus–response relations in summarizing the results of quantifying experimental psychology data, it is wiser to write of externally observable events for stimuli and to write specifically of reports of personal sensory experiences or choice actions, leaving responses to include a wide diversity of behaviors, including physiological processes that have no necessary conscious correlates.

Psychophysics usually leads to some mathematical representation of mapping from inputs to outputs, in which the environment is given and the behavior is dependent and the mapping is written outside time, being static and not dynamic. This does not exclude the use of psychophysical methods in studies of topics such as fatigue or vigilance, when behavior is variable and even transiently erratic.