riment suggested by Robert Z. Norman, a Michigan mathematics student. Carried out with visual stimuli, the critical ﬁnding was that a second choice made in a four alternative forced-choice test, when the ﬁrst choice was incorrect, was correct with probability greater than 1/3 and that the probability of it being correct increased with signal strength (Swets et al. 1961, Swets 1964, Chap. 1).
Validating the rating method, as mentioned above, had the important eﬀect of providing an eﬃcient method for obtaining empirical ROCs. Whereas under the yes–no method the observer is induced to set a diﬀerent cutpoint in each of several observing sessions (each providing an ROC point), under the rating method the observer eﬀectively maintains several decision cutpoints simultaneously (the boundaries of the rating categories) so that several empirical ROC points (enough to deﬁne a curve) can be obtained in one observing session.
7. Dissemination Of SDT In Psychology
Despite the growing evidence for it, acceptance of SDT was not rapid or broad in psychophysical circles. This was partly due to threshold theory having been ingrained in the ﬁeld for a century (as a concept and a collection of methods and measures), and probably because SDT arose in an engineering context (and retained the engineers’ terminology), the early visual data were noisy, and the ﬁrst article (Tanner and Swets 1954) was cryptic. Dissemination was assisted when J. C. R. Licklider brought Swets and Green to the Massachusetts Institute of Technology where they participated in Cambridge’s hotbed of psychophysics and mathematical psychology, and where oﬀering a special summer course for postgraduates led to a published collection of approximately 35 of the articles on SDT in psychology that had appeared by then, along with tables of d’ (Swets 1964). Licklider also hired both of them part-time at the research ﬁrm of Bolt Beranek and Newman Inc., where they obtained contract support from the National Aeronautics and Space Administration to write a systematic textbook (Green and Swets 1966). Meanwhile, Tanner mentored a series of exceptional graduate students at Michigan. All were introduced by Licklider to the Acoustical Society of America where they enjoyed a feverishly intense venue for discussion of their ideas at biannual meetings and in the Society’s journal. Another factor was the active collaboration with Tanner of James P. Egan and his students at Indiana University.
8. Extensions Of SDT In Psychology
Egan recognized the potential for applying SDT in psychology beyond the traditional psychophysical tasks. He extended it to the less tightly deﬁned vigilance task, that is, the practical military and industrial observing task of ‘low-probability watch’ (Egan et al. 1961–see Swets 1964, Chap. 15), and also to speech communication (Egan and Clarke 1957–see Swets 1964, Chap. 30). He also brought SDT to purely cognitive tasks with experiments in recognition memory (see Green and Swets 1966, Sect. 12.9). Applications were then made by others to those tasks, and also to tasks of conceptual judgment, animal discrimination and learning, word recognition, attention, visual imagery, manual control, and reaction time (see Swets 1996, Chap. 1). A broad sample of empirical ROCs obtained in these areas indicates their very similar forms (Swets 1996, Chap. 2). An Annual Review chapter reviews applications in clinical psychology, for example, to predicting acts of violence (McFall and Treat 1999).
9. Applications In Diagnostics
An analysis of performance measurement in information retrieval suggested that two-by-two contingency tables for any diagnostic task were grist for SDT’s mill (Swets 1996, Chap. 9). This idea was advanced considerably by Lusted’s (1968) application to medical diagnosis. A standard protocol for evaluating diagnostic performance via SDT methods, with an emphasis on medical images, was sponsored by the National Cancer Institute (Swets and Pickett 1982). By 2000, ‘ROC’ is speciﬁed as a key word in over 1000 medical articles each year, ranging from radiology to b