Signal Detection Theory
Psychophysics depends exclusively on subjective reporting of sensation, including sound, vision, touch, odor, and taste stimuli. To help overcome the problem of guessing by subjects, the signal detection theory was developed (Green & Swets, 1966). Signal detection theory approaches the subject's behavior in detecting a threshold as a form of decision-making. In each trial of a signal detection test, two sets of two probabilities are possible: the sensory stimulus can be presented or withheld, and the subject can report perceiving the stimulus or not. If a stimulus is presented and the subject says yes, the trial is a "hit." If no stimulus is presented but the subject still says yes, it is a "false alarm" and might indicate that the subject is motivated to guess. If a stimulus is presented and the subject says no, it is a "miss" and gives information on the subject's ability to detect the stimulus. Finally, if no stimulus is presented and the subject says no, it is a correct rejection. From these data, it is possible to plot a subject's responses when the intensity of the stimulus is varied. The resulting curve is called the receiver operating characteristic (ROC), and provides additional information on the detection of sensory thresholds. By including the subject's psychological characteristics as well as the subjective reporting of sensation, signal detection theory has helped psychologists learn more about how sensation and perception operate. Recent research using a signal detection approach has found the perceptual sensitivity of people with schizophrenia (a severe psychological disorder) to be significantly lower than that of healthy individuals (Mussgay & Hertwig, 1990).