Copyright 2006 Psychonomic Society, Inc. 474Journal2006, ?? (?), ???-???Vancouver, Toronto, Montreal, Austin: Given a list of items to remember, people show a memory advantage for an item that differs from others in some way, such as an American city (Austin) in a list of Canadian cities (Vancou-ver, Toronto, Montreal). This robust memory phenomenon is known as the von Restorff effect (von Restorff, 1933) and has been established in various forms. For example, deviant faces (Valentine, 1991), behaviors (Stangor & McMillan, 1992), and category members (Palmeri & Nosofsky, 1995) result in enhanced memory. Whether or not information is deviant depends on how humans structure their environ-ment (Schmidt, 1991). In the example above, people dis-cover the structure that most list items are Canadian cities. Austin is novel in the context of this structure.Novelty detection is the flip side of stimulus generaliza-tion and likely plays a central role in our mental develop-ment. Indeed, infants tend to show preference for a novel stimulus once they habituate to a familiar one (Fantz, 1964), and this ability to respond to novelty is predictive of later intelligence (McCall & Carriger, 1993). Novelty affects our mental activities. For instance, deviant individ-uals are judged as more influential than others, and more behaviors of deviant individuals are remembered (Taylor, Fiske, Etcoff, & Ruderman, 1978). Research in cognitive neuroscience has focused on identifying the neural cir-cuits underlying novelty processing (see, e.g., Kishiyama, Yonelinas, & Lazzara, 2004; Ranganath & Rainer, 2003).Despite the widespread interest in novelty effects, the basis for these effects is not well understood. Earlier ex-planations emphasized differential attention allocated to oddball items at the time of encoding (e.g., Jenkins & Postman, 1948). However, these explanations have been challenged by work demonstrating memory advantages for deviant items presented at the beginning of a study list (e.g., Kelley & Nairne, 2001). More recent explanations focus on the processing of similarities and differences among stimulus items (Fabiani & Donchin, 1995; Hunt & Lamb, 2001; Nairne, 2006). According to Hunt and Lamb, oddball items, which differ from other items, become iso-lated by grouping of other items that share similarities.In the present work, we examine the role of similarity among deviant and other items in enhanced memory. Most explanations center on the advantage conferred to isolated items (see, e.g., Hunt & Lamb, 2001). In the isolation ac-count, deviant items are better remembered when they are more dissimilar to other items. Highly dissimilar items oc-cupy an isolated region in a representational space (Busey & Tunnicliff, 1999) and do not activate many stored items during retrieval (Nairne, 2006). The isolation account at-tributes novelty effects to reduced confusion with other items.However, recent category learning research has brought the isolation account into question and suggested instead that differentiation underlies the enhanced oddball mem-ory (Sakamoto & Love, 2004). Interitem similarity rela-tions play opposing roles in these two accounts. In the dif-ferentiation account, oddball items are remembered better when they are more similar to other items. Items that are highly similar to other items yet deviate on a property are stored in a dense region and highly confusable with other items. The differentiation account attributes novelty ef-fects to finer-grained memory traces resulting from an This work was supported by AFOSR Grant FA9550-04-1-0226 and NSF CAREER Grant 0349101 to B.C.L. Correspondence concerning this research should be addressed to Y. Sakamoto or B. C. Love, Depart-ment of Psychology, University of Texas at Austin, One University Sta-tion A8000, Austin, TX 78712 (e-mail: [email protected] or [email protected]. Web site: love.psy.utexas.edu/).Vancouver, Toronto, Montreal, Austin: Enhanced oddball memory through differentiation, not isolationYAsuAki sAkAMoTo and BrAdlEY C. loVEUniversity of Texas, Austin, TexasWhat makes a person, event, or object memorable? Enhanced memory for oddball items is long es-tablished, but the basis for these effects is not well understood. The present work clarifies the roles of isolation and differentiation in establishing new memories. According to the isolation account, items that are highly dissimilar to other items are better remembered. in contrast, recent category learning studies suggest that oddball items are better remembered because they must be differentiated from similar items. The present work pits the differentiation and isolation accounts against each other. The results suggest that differentiation, not isolation, leads to more accurate memory for deviant items. in contrast, gains for isolated items are attributable to reduced confusion with other items, as opposed to preferential storage.Psychonomic Bulletin & Review2006, 13 (3), 474-479ENHANCED ODDBALL MEMORY THROUGH DIFFERENTIATION 475item’s contrast with highly similar items that establish a context. In support of the differentiation account, people notice changes in deviant items more accurately (Good-man, 1980) and store more item-specific information of deviant items (Schmidt, 1985).The isolation and differentiation accounts have not been distinguished from each other in previous research. One reason is that oddball items are usually not only iso-lated but also differentiated. In Figure 1, for example, the octagons in the top and bottom panels are both isolated in that they have a shape that the hexagons do not have. Both octagons are also differentiated in that they share properties with the other items (e.g., size) but deviate on shape. However, the two octagons differ in their degrees of isolation and differentiation. The top octagon is more dif-ferentiated, since it has the same color as the other items, whereas the bottom octagon is more isolated, since its color is dissimilar to that of the other items.In the present work, we pitted the isolation and differen-tiation accounts of enhanced memory against each other by varying interitem similarity relations. To foreshadow our results, we mention that isolation and differentiation manipulations lead to qualitatively different memory ad-vantages. As the differentiation account predicts, finer-grained memory traces result for deviant items that are similar to other items. As the isolation account predicts,
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