What sort of measurement is psychophysical measurement?

THE thesis of this article has both a negativeand a positive aspect. The negative oneholds that psychophysical measurement is not of a character closely analogous to either fundamental or derived physical measurement. Whatever loudness may be, I endeavor to establish that it probably is not a measure much like mass or energy or density. In brief, the reason is that psychophysical measures do not exhibit any fixed relation to physical measures and most likely not to one another when examined over individuals. This is reflected in the absence of any structure to the units of psychophysical measures. The positive thesis is that man—and any other organism—is, among other things, a measuring de-vice, in function not unlike a spring balance or a voltmeter, which is capable of transforming many kinds of physical attributes into a common measure in the central nervous system. According to this view, the task of psychophysics is to unravel the nature of that device. The difficulty in doing so stems from several facts: as compared with man-made, special-purpose devices, higher organisms are both complex and flexible measuring devices; their overall behavior does not clearly suggest the nature of the receding of signals; some responses depend on peculiar nonlinear processing of the sensory information; and each individual within a species is calibrated somewhat differently. To flesh out and make this view reasonably clear, we must know something of physical measurement and of psychophysics. Since the details of the nature of physical measurement, especially the abstract theory, are probably not very familiar 1 The preparation of this article was supported by a