Journal of Experimental Psychology Learning Memory and Cognition 2003 Vol 29 No 4 626 640 Copyright 2003 by the American Psychological Association Inc 0278 7393 03 12 00 DOI 10 1037 0278 7393 29 4 626 Learning Myopia An Adaptive Recency Effect in Category Learning Matt Jones Winston R Sieck University of Michigan Ohio State University Recency effects REs have been well established in memory and probability learning paradigms but have received little attention in category learning research Extant categorization models predict REs to be unaffected by learning whereas a functional interpretation of REs suggested by results in other domains predicts that people are able to learn sequential dependencies and incorporate this information into their responses These contrasting predictions were tested in 2 experiments involving a classification task in which outcome sequences were autocorrelated Experiment 1 showed that reliance on recent outcomes adapts to the structure of the task in contrast to models predictions Experiment 2 provided constraints on how sequential information is learned and suggested possible extensions to current models to account for this learning Recency effects REs are a robust phenomenon in cognitive psychology REs are said to occur whenever more recent experiences are better remembered or are more influential in judgments about present situations For example in research on verbal working memory REs are arguably among the most fundamental established phenomena most commonly seen as increased performance on the final positions in free or serial recall tasks e g Crowder 1972 Murdock 1962 Similar results have since been observed in visuo spatial working memory Broadbent Broadbent 1981 as well as in animals Thompson Herman 1977 Wright Santiago Sands Kendrick Cook 1985 REs in working memory have often been attributed to spontaneous decay of stored information Baddeley 1986 Burgess Hitch 1999 however this simple interpretation has been called into question by recent results showing that the rate of information loss can change adaptively in response to temporal statistics of the task R B Anderson Tweney Rivardo Duncan 1997 This flexibility is more consistent with a functional account of working memory J R Anderson Schooler 1991 2000 Schacter 1999 and suggests that there is more underlying the phenomenon than simple architectural constraints Another area in which REs commonly arise is animal conditioning experiments Common learning phenomena that depend on trial order such as extinction counterconditioning and discrimination reversal learning all fall into the category of REs because they are characterized by behavior at the conclusion of learning being based primarily on the most recent second phase of training rather than an average of both phases However the existence and magnitude of such trial order effects depend crucially on the relationship of physical and temporal contexts among the phases of training and testing in a manner that is easily argued to be rational and adaptive see Bouton 1993 for a review Similar REs are commonly observed in human experimentation with probability learning for instance as a tendency to respond with whatever option was given as correct on the previous trial independent of the reinforcement pattern over the prior history of the task e g Jarvik 1951 Nicks 1959 This effect is easily predicted both by associative learning models and by models that assume decay of memory for past events However such theories have trouble with further results indicating that REs in these tasks are subject to learning effects in response to sequential dependencies in the target sequence In particular when outcomes of successive trials are made to depend on each other rather than being independently sampled observed REs adapt accordingly N H Anderson 1960 Some evidence for order effects has also been found in multiplecue category learning MCCL For instance Busemeyer and Myung 1988 found that humans subjective prototypes for groups of random dot patterns showed a temporal bias involving both primacy and REs Still a detailed investigation of sequential effects in MCCL has yet to be performed This situation is reflected in current models of the task which either do not address REs or treat them as static by products of other processes Such a stance is at variance with the results from other domains which suggest instead that REs may be adaptive and sensitive to statistical characteristics of the task In particular when viewed as an extension of probability learning MCCL might be expected to produce effects similar to those mentioned above wherein REs adapt to sequential dependencies among outcomes On the other hand the presence of variable cues gives two reasons that the pattern might be different First there is evidence that REs in MCCL are more complex in that they depend on the similarity between present and previous stimuli Sieck 2000 Second whereas uncued learners have little to attend to but the target sequence subjects in MCCL tasks have more tangible stimuli about which they are explicitly instructed to learn This attention shift combined with the memory demands associated with using Matt Jones Department of Psychology University of Michigan Winston R Sieck Department of Psychology Ohio State University This work was supported in part by National Science Foundation Grant SES 9911301 Correspondence concerning this article should be addressed to Matt Jones who is now at the Department of Psychology University of Texas at Austin 1 University Station A8000 Austin Texas 78712 Email mattj psy utexas edu 626 ADAPTIVE RECENCY multiple cues could conceivably eliminate or greatly attenuate any learning of sequential dependencies In the remainder of this article we describe a focused exploration of REs in category learning intended to address these issues Our primary aims are to investigate a the presence and nature of REs in cued category learning b the role played by cues and by stimulus similarity and c potential learning effects in response to sequential dependencies in the target sequence along with the mechanisms underlying such effects We begin with a more detailed account of results from the probability learning literature in which REs have been well documented and extensively investigated Next we discuss some of the more popular current models of category learning and present a simulation study to evaluate their predictions concerning REs in situations
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