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Suppose that, with rather few exceptions, the assignment of a number to a stimulus on one trial of a magnitude estimation or category judgement experiment serves as the point of reference for choosing an appropriate assignment on the next trial. This principle of relative judgement—relative to the immediate context—is developed to generate models for both magnitude estimation and category judgement experiments. It is applied, in particular, to the explanation of three, hitherto unrelated, phenomena: these are (a) the limited transmission of information in category judgements; (b) sequential constraints on the resolving power of category judgements; and (c) the autocorrelation of successive numerical magnitude estimates. Finally, some comparison is made between the principle of relative judgement introduced here and other contemporary ideas which have been addressed to one or more of these three critical phenomena.

This paper sets out quantitative foundati ons for testing the idea that memory is served by two distinct storage mechanis ms, a short-term and a separate long-te rm store, using data fro m the single-trial free-recall experiment by M urdock and Oka da (1970). In single-trial free recall one can observe which word is recalled next and how long that recall takes, but that is all. So justi® cation for two separate stores must turn either on the probabilities of recall, or on the latencie s, for pa rticular serial position s in the stimulus list.(a) Nearly one-thir d of all recalls after the ® rst are successors (Word n+1 im mediately follow ing recall of Word n). So recall is do minated, not by absolute serial position (as a short-term store would require), but by position relative to the preceding recall.(b) To a ® rst approximation, all ® rst recalls have the same latency distribu tion except for Word 1. A co mmon latency distribution is co mpatible with a single store. A n exp lanation is offered why Word 1 should take longer, in which Word 1 is the second retrieval fro m a co m mon store.The idea of two separate stores appears to lack experimental support.Cet article propose un test quantita tif de l' ide e selon la quelle la me moire co mprendrait deux me canis mes distincts d' em magasinage, un me canis me a Á court ter me et un me canis me a Á long terme. Les donne es d' une expe rience de M urdock et Okada (1970), dans laquelle un seul essai de rappel libre e tait pre sente , sont utilise es. D ans cette taà che, il est possible de ve ri® er quel mot est rappele apre Á s un autre mot et co mbien de te mps prend ce rappel, mais ce sont la Á les deux seules mesures disponibles. D ans ces conditio ns, la justi® cation de l' existence de deux syste Á mes se pa re s doit eà tre base e soit sur les probabilite s de rappel ou sur le te mps de latence pour des position s se rielles spe ci® ques.(a) Pre Á s d' un tiers de tous les mots rappele s apre Á s le premier sont des successeurs (M ot n+1 suit im me diate ment le rappel du M ot n). Le rappel est donc do mine par la positio n relative de l' ite m rappele pre ce dem ment et non pas par la pos ition se rielle absolue (co mme l' exigerait l' hypothe Á se d' un syste Á me a Á court terme).(b) Tous les premiers rappels ont approximative ment la meà me distribu tion de latence, excepte le M ot 1. Cette distribu tion de latence est co mpatible avec un syste Á me unitaire de me moire. Le te mps de latence plus long pour le M ot 1 serait attribuable au fait que celui-c i est le second a Á eà tre re cupe re d' un syste Á me co m mun.L' ide e de deux syste Á mes se pare s de me moire semble manquer de appui empirique.IN TERNAT IO NAL JOU RNA L OF PSYCH OLOGY, 1999 , 34 (5/6), 419± 426Request s for reprints should be addresse d to D onald La ming,