Dimension-Wide vs. Exemplar-Specific Attention in Category ...

distributed to the non-rule dimensions than exemplarsrepresenting rule-following items. Moreover,as predicted more attention was distributed to thenon-rule dimensions for the exemplar encoding categoryB’s exception than for the exemplar encodingcategory A’s exception.There were more errors involving the category Bexception than the category A exception becausemore rule-following items in category A were similarto the category B exception. Such errors were accentuatedin ESSW-ALCOVE, and the category B exceptionresulted in more uniform attention. ESSW-ALCOVE predicts a memory advantage for the categoryB exception because it is differentiated frommany similar rule-following items from category A.Filtration and CondensationIncorporating exemplar-specific attention and accentuatederrors allowed ALCOVE to predict previouslychallenging data. It is crucial that a modelthat incorporates new mechanisms can still accountfor other basic psychological phenomena. Examiningfiltration and condensation tasks (Gottwald &Garner, 1975; Kruschke, 1993, Matsuka, in press) isimportant because these tasks investigate how humansallocate attention.Humans (and ALCOVE) find it easier to learn filtrationtasks, in which information from only onedimension is required for perfect classification, thancondensation tasks, in which information from two(or more) dimensions is needed (e.g., Kruschke,1993). This filtration advantage was predicted byESSW-ALCOVE (and ES-ALCOVE). In filtration,all exemplars attend to the predictive dimension.This leads to increased psychological distances betweencategory A and category B members. In condensation,some items are closer to the opposing category’sexemplars even with exemplar-specific attention,and ESSW-ALCOVE has less “confirmations”from some exemplars. ESSW-ALCOVE finds it easierto learn the filtration task, in which it receivesmore “evidence” for correct category membership.DiscussionHumans can flexibly attend to different dimensionsof an item depending on the values of the dimensionsthat are not critical for classification (Aha &Goldstone, 1992). Such flexible attention allowedES-ALCOVE to differentiate exceptions from rulefollowingitems and predict a memory advantage forexceptions. In ES-ALCOVE, each exemplar selectedwhich dimensions to attend to. ES-ALCOVE attendedto the non-rule dimensions of exemplars encodingexceptions but to the rule dimension of exemplarsencoding rule-following items. This differentialattention made exceptions distinctive in memory.However, ES-ALCOVE was unable to accountfor the finding that memory for a violating itemis stronger when the violated structure is stronger.This finding was predicted by ESSW-ALCOVE,which accentuated errors. With errors raised tothe 10th power, ESSW-ALCOVE distinguished importanterrors (e.g., miss-classification) from trivialones (e.g., correct classification with 90% confidencelevel). ESSW-ALCOVE learned attentionmore rapidly in response to larger errors and minimizedthe impact of smaller errors. A similar effectcan be obtained by updating the attention weightsmultiple times on each training trial (e.g., Kruschke,2001). ESSW-ALCOVE better remembered itemsthat violated a stronger rule because those itemswere associated with “important” errors.In addition to the exception memory findings reviewedin this paper, ESSW-ALCOVE was ableto predict a filtration advantage. We should notethat ALCOVE that accentuated errors withoutexemplar-specific attention was unable to predict theexception memory findings. Thus, ALCOVE needsboth exemplar-specific attention and accentuated errorsto account for all of the findings described inthis paper. One question to ask is whether thesemechanisms are also required by other models.Clustering ApproachSUSTAIN (Love et al., 2004), which uses dimensionwideattention, can predict the memory advantagefor exceptions as well as the greater memory advantagefor exceptions that violate a stronger rule. SUS-TAIN clusters together similar items and recruits anew cluster in response to a prediction error. SUS-TAIN develops rule-following clusters and shifts attentionto the rule dimension. All clusters sharethe same attention along a dimension. When anexception item elicits a prediction error, SUSTAINrecruits an additional cluster to encode the item.While rule-following items tend to cluster with oneanother, each exception item will be isolated in itsown cluster. This differential storage makes exceptionsmore distinctive in memory.SUSTAIN also predicts better recognition forthe category B exception that violates more rulefollowingitems from category A. A prediction erroroccurs when SUSTAIN attempts to cluster togetherhighly similar items from competing categories.The exception clusters brought about sucherrors by attracting rule-following items from theopposing category. Because there were more categoryA rule-following items, there were more opportunitiesfor such errors involving the category Bexception to occur, and a greater number of categoryA rule-following clusters were recruited. Theseclusters formed a highly contrastive backdrop for thecategory B exception and enhanced recognition.As ESSW-ALCOVE, SUSTAIN treats “important”and “negligible” errors differently. Large discrepanciesbetween target and predicted output valuesresult in prediction errors. SUSTAIN recruits

new clusters in response to such errors but “ignores”small discrepancies.SUSTAIN’s success in predicting these results usingdimension-wide attention suggests that attentionmechanisms interact with internal representations ofa model (cf., Matsuka, in press). Clustering allowsSUSTAIN to be sensitive to rule violation withoutexemplar-specific attention. In contrast, by storingevery studied item, ALCOVE needs exemplarspecificattention to capture the rule-violating natureof exceptions.Future DirectionA more flexible model may use dimension-wide orexemplar-specific attention depending on a giventask. For example, humans may initially be biasedto attend to the same dimensions for all exemplars,analogous to a prior, but over time optimize learningby utilizing a separate attention for certain items.In learning about the rule-plus-exception categorystructures, humans may initially attend to the ruledimension for all the items. When an exception appearsand a prediction error occurs, a separate attentionmay be used for the exception. Such processessuggest that humans have simplicity bias (cf., Matsuka,2004). For example, filtration tasks may resultin dimension-wide attention, whereas condensationtasks may lead to exemplar-specific attention. Futurework should examine when exemplar-specific ordimension-wide attention is more appropriate.AcknowledgmentsThis work was supported by AFOSR Grant FA9550-04-1-0226 to B.C. Love, and by the James McDonnellFoundation and the National Science Foundation(EIA-0205178).ReferencesAha, D. W., & Goldstone, R. L. (1992). Conceptlearning and flexible weighting. In Proceedings ofthe 14th Annual Conference of the Cognitive ScienceSociety (pp. 534–539). Hillsdale, New Jersey:Lawrence Erlbaum Associates.Allen, S. W., & Brooks, L. R. (1991). Specializingthe operation of an explicit rule. Journal of ExperimentalPsychology: General, 120, 3–19.Barsalou, L. W., & Medin, D. L. (1986). Concepts:Static dimensions or context-dependent representations?Cahiers de Psychologie Cognitive, 6, 187–202.Erikson, M. A., & Kruschke, J, K. (1998). Rulesand exemplars in category learning. Journal ofExperimental Psychology: General, 127, 107–140.Gottwald, R. L., & Garner, W. R. (1975). Filteringand condensation tasks with integral and separabledimensions. Perception & Psychophysics, 2,50–55.Kruschke, J. K. (1992). ALCOVE: An exemplarbasedconnectionist model of category learning.Psychological Review, 99, 22–44.Kruschke, J. K. (1993). Three principles for modelsof category learning. In G. V. Nakamura, R.Taraban, & D. L. Medin (Eds.) Categorization byhuman and machines: The psychology of learningand motivation (Vol. 29, pp. 57–90). San Diego,CA: Academic Press.Kruschke, J. K. (2001). Toward a unified model ofattention in associative learning. Journal of MathematicalPsychology, 45, 812–863.Lewandowsky, S., Kalish, M., & Ngang, S. K. (2002).Simplified learning in complex situations: Knowledgepartitioning in function learning. Journal ofExperimental Psychology: General, 131, 163–193.Love, B. C., Medin, D. L., & Gureckis, T. M. (2004).SUSTAIN: A Network Model of Human CategoryLearning. Psychological Review. In press.Matsuka, T. (in press). Generalized exploratorymodel of category learning. International Journalof Computational Intelligence.Matsuka, T. (2004). Biased stochastic learning incomputational model of category learning. In Proceedingsof the 26th Annual Conference of the CognitiveScience Society.Medin, D. L., & Schaffer, M. M. (1978). Contexttheory of classification learning. Psychological Review,85, 207–238.Nosofsky, R. M. (1986). Attention, similarity,and the identification-categorization relationship.Journal of Experimental Psychology: General,115, 39–57.Nosofsky, R. M., Palmeri, T. J., & McKinley, S. C.(1994). Rule-plus-exception model of classificationlearning. Psychological Review, 101(1), 53–79.Palmeri, T. J., & Nosofsky, R. M. (1995). Recognitionmemory for exceptions to the category rule.Journal of Experimental Psychology: Learning,Memory, & Cognition, 21, 548–568.Pinker, S. (1991). Rules of language. Science, 253,530–535.Rojahn, K., & Pettigrew, T. F. (1992). Memoryfor schema-relevant information: A meta-analyticresolution. British Journal of Social Psychology,31(2), 81–109.Sakamoto, Y., & Love, B. C. (in press). Schematicinfluences on category learning and recognitionmemory. Journal of Experimental Psychology:General.Smith, E. E., & Langston, C., & Nisbett, R. E.(1992). The case for rules in reasoning. CognitiveScience, 16, 1–40.