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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.

Recognition memory, source memory, and exclusion performance are three important domains of study in memory, each with its own findings, it specific theoretical developments, and its separate research literature. It is proposed here that results from all three domains can be treated with a single analytic model. This article shows how to generate a comprehensive memory representation based on multidimensional signal detection theory and how to make predictions for each of these paradigms using decision axes drawn through the space. The detection model is simpler than the comparable multinomial model, it is more easily generalizable, and it does not make threshold assumptions. An experiment using the same memory set for all three tasks demonstrates the analysis and tests the model. The results show that some seemingly complex relations between the paradigms derive from an underlying simplicity of structure.

A seminal experiment found that the reported time of a decision to perform a simple action was at least 300 ms after the onset of brain activity that normally preceded the action. In Experiment 1, we presented deceptive feedback (an auditory beep) 5 to 60 ms after the action to signify a movement time later than the actual movement. The reported time of decision moved forward in time linearly with the delay in feedback, and came after the muscular initiation of the response at all but the 5-ms delay. In Experiment 2, participants viewed their hand with and without a 120-ms video delay, and gave a time of decision 44 ms later with than without the delay. We conclude that participants' report of their decision time is largely inferred from the apparent time of response. The perception of a hypothetical brain event prior to the response could have, at most, a small influence.

This research studies lateral interference among items in the visual field under conditions in which central cognitive factors such as attention and memory limitations are eliminated or controlled for. Under these conditions lateral masking is still found, and it is still asymmetrical (peripheral items interfere with recognition of central items more than central with peripheral). These experiments therefore add to the evidence that both lateral interference and the asymmetry of interference have a component that does not result from cognitive strategies. The experiments also add to the evidence that the asymmetry effect at the sensory level can be attributed to the falloff in acuity from the center to the periphery of the retina, since the mean eccentricity of the target-mask cluster is more peripheral with a peripheral mask than with a central mask. The hypothesis is advanced that the asymmetry effect, as well as lateral interference itself, at the sensory level results from the grouping of target and mask into a single Gestalt-like configuration. The final experiment in the series supports this hypothesis.