Ching-Fan Sheu, Ph.D.


Testing Global Memory Models Using ROC Curves

Coauthors:
Roger Ratcliff, Northwestern University
Scott D. Gronlund, University of Oklahoma

Global memory models are evaluated by using data from recognition memory experiments. For recognition, each of the models gives a value of familiarity as the output from matching a test item against memory. The experiments provide ROC (receiver operating characteristic) curves that give information about the standard deviations of familiarity values for old and new test items in the models. The experimental results are consistent with normal distributions of familiarity (a prediction of the models). However, the results also show that the new-item familiarity standard deviation is about 0.8 that of the old-item familiarity standard deviation and independent of the strength of the old items (under the assumption of normality). The models are inconsistent with these results because they predict either nearly equal old and new standard deviations or increasing values of old standard deviation with strength. Thus, the data provide the basis for revision of current models or development of new models.

© 1992, American Psychological Association
Psychological Review, Vol. 99, No. 3, 518-535

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Causal inferences as perceptual judgments

Coauthor:
John R. Anderson, Carnegie Mellon University


We analyze how subjects make causal judgments based on contingency information in two paradigms. In the discrete paradigm, subjects are given specific information about the frequency a, with which a purported cause occurs with the effect; the frequency b, with which it occurs without the effect; the frequency c, with which the effect occurs when the cause is absent; and the frequentcy d, with which both cause and effect are absent. Subjects respond to P1 = a/(a +b) and P2 = c/(c+ d). Some subjects' ratings are just a function of P1, while others are a function of AP = P1 - P2. Subjects' post-experiment reports are accurate reflections of which model they use. Combining these two types of subjects results in data well fit by the weighted AP model (Allan, 1993). In the continuous paradigm, subjects control the purported causes (by clicking a mouse) and observe whether an effect occurs. Because causes and effects occur continuously in time, it is not possible to explicitly pair causes and effects. Rather, subjects report that they are responding to the rate at which the effects occur when they click versus when they do not click. Their ratings are a function of rates and not probabilities. In general, we argue that subjects' causal ratings are judgments of the magnitude of perceptually salient variables in the experiment.

© 1995, Psychonomic Society, Inc.
Memory & Cognition, 23(4), 510-524

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