THEORY, DATA, AND MEASURES
The three chapters of Part I describe: (a) the origins of signal detection theory and ROC analysis in statistics and engineering and the relation of these concepts to historical concepts in psychophysics and psychology; (b) experimental data in the form of empirical ROCs that support signal detection theory and ROC analysis in psychology and diagnostics; and (c) the implications of those ROC data both for psychological theory and for the several measures of discrimination performance that have been used in psychology and in diagnostic fields.
Chapter I describes the relevant psychophysical theory beginning with Gustav Fechner in 1860. It acknowledges Louis Leon Thurstone's 1920s conception of the two stimulus categories to be distinguished as leading to two overlapping (bell-shaped) distributions on an observation variable. In Thurstone's theory, the two stimuli are symmetrical as far as distinguishing between them is concerned, and so a criterion is set on the observation variable where their distributions cross one another. This chapter goes on to show how H. Richard Blackwell in the 1950s extended the conception of the overlapping distributions from Thurstone's consideration of the "paired-comparison," or recognition, task (which Blackwell termed "two-alternative forced-choice") to the "yes- no," or detection, task. This extension was made in the interests of threshold theory, which detection theory replaces, but it was a step along the way, inasmuch as the yes-no task lies at the heart of signal detection theory and is the basis for the ROC. As the last