The Yes-No Experiment: Sensitivity
In this book, we analyze experiments that measure the ability to distinguish between stimuli. An important characteristic of such experiments is that observers can be more or less accurate. For example, a radiologist's goal is to identify accurately those X-rays that display abnormalities, and participants in a recognition memory study are accurate to the degree that they can tell previously presented stimuli from novel ones. Measures of performance in these kinds of tasks are also called sensitivity measures: High sensitivity refers to good ability to discriminate, low sensitivity to poor ability. This is a natural term in detection studies—a sensitive listener hears things an insensitive one does not—but it applies as well to the radiology and memory examples.
We begin with a memory experiment. In a task relevant to understanding eyewitness testimony in the courtroom, participants are presented with a series of slides portraying people's faces, perhaps with the instruction to remember them. After a period of time (and perhaps some unrelated activity), recognition is tested by presenting the same participants with a second series that includes some of the same pictures, shuffled to a new random order, along with a number of “lures”—faces that were not in the original set. Memory is good if the person doing the remembering properly recognizes the Old faces, but not New ones. We wish to measure the ability to distinguish between these two classes of slides. Experiments of this sort have been performed to compare memory for faces of different races, orientations (upright vs. inverted), and many other variables (for a review, see Shapiro & Penrod, 1986).