Psychophysics

Abstract Psychophysics is the quantitative study of the relation between stimulus and sensation or sensory response. As such, it is concerned with the following questions: (1) How much stimulation is required to produce a sensation or sensory response? (2) How much must a stimulus be changed for the change to be detected? (3) In what way or ways must a stimulus be changed to be perceptually equivalent to another? (4) How does the sensation or sensory response change with changes in stimulus magnitudes? Answers to these questions (among others) are provided by psychophysical methods. These consist of the three classical methods—limits, adjustment, and constant stimuli—that were advanced, but not originated, by Gustav T. Fechner (1801–1887) for use in determining thresholds, for numerous suprathreshold psychophysical scaling methods used for deriving measures of sensation magnitude, and for signal detection theory methods used in providing measures of basic sensory sensitivity, minimally contaminated by motivational and attitudinal biases. Although employed primarily with human subjects, several of the psychophysical methods have been adapted for studying nonhuman sensitivity (Stebbins, 1970).