(Qest-ce que cest?)
Psychophysics is the scientific study of the relationship between stimuli (specified in physical terms) and the sensations and perceptions evoked by these stimuli. The term psychophysics is used to denote both the substantive study of stimulus-response relationships and the methodologies used for this study.
This is but one example of what psychophysics can provide. In the Munsell Lab we use psychophysics for a variety of different purposes. We have subjects judge the magnitude of color differences against a standard color difference in order to derive color tolerances for industrial purposes. We have subjects perform color matching experiments to understand the variability in color differences between individuals. Many times we have subjects make judgment on images to see how different displays or imaging devices and techniques affect image quality.
In the definition above, you will notice that psychophysics refers not only to the methodology but also the study of the methodology.