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Some applications of signal detection theory (SDT) in the study of memorial processes are critically reviewed in four categories: (a) uses of SDT to scale memory strength, (6) use of SDT in criterial interpretations of data that seem to indicate forgetting, (c) attempts using SDT to determine the form of trace storage and to settle the question of all-or-none learning, and (d) extensions of SDT to scale memory-based discriminability in finer analyses of retention. The techniques that SDT offers the student of memory are explained, their limitations and past misapplications are discussed, their advantages in various situations are enumerated, and future applications are suggested.Signal detection theory (SDT) has had a considerable influence on psychological experimentation and theory since it began to find a place in the psychological literature in the late 1950s and early 1960s. Although the relevance of SDT is most obvious in areas concerned with sensory and perceptual processes, the techniques of SDT have potentially a much wider application, and the impact of this theory is only beginning to be felt in many areas where it has much to offer. One such area of moderate impact but great potential for SDT is human learning and retention. Since Egan (1958) applied SDT suc-1 This paper, a general review of issues in the application of signal detection theory to the study of memory, was received as an ordinary paper. The paper which follows it was commissioned by the editor. This paper is published out of its normal order of publication because it provides an introduction to assist the reader who is unfamiliar with the issues discussed in the commissioned paper, which follows.2 This paper grew out of a series of luncheon talks given by the present author at the

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These experiments show that the perceptual organization of a multielement display affects both the speed and accuracy with which a target letter in it is detected. The first two experiments show that a target is detected more poorly if it is arranged in good form (a perceptual Gestalt) with noise elements than if it is not. This effect is not confounded with target-noise proximity or display size, and it holds for stimuli terminated by the subject's response as well as for stimuli of very brief duration. Increasing the number of noise elements can actually improve performance if the added noise elements increase the degree to which the noise elements form perceptual groups separately from the target. A third experiment tries out a new method for scaling the perceptual structure of an array, and it shows that the main features of the first two experiments can be predicted from the scaled perceptual structure of the arrays they used.

This article studies the processing of pictures and words as symbols. Pictures lead to faster and more accurate responses than words when the task is to decide which member of a pair of pictures or words denotes the larger or smaller object. The present experiments show that the superiority of pictures results from the fact that pictures are interpreted more quickly than words, but that after the interpretation is made, processing is the same. These experiments also give evidence that pictures and words are both processed in terms of linguistic codes rather than mental images. The results are well accounted for by an information-processing model that is based on two general assumptions: (a) The stimuli and the instructions are represented as discrete codes, and (b) processing proceeds until one and only one of the stimulus codes is the same as the code for the instructions.