Psychonomic Bulletin Review Journal 2006 13 3 474 479 Vancouver Toronto Montreal Austin Enhanced oddball memory through differentiation not isolation Yasuaki Sakamoto and Bradley C Love University of Texas Austin Texas What makes a person event or object memorable Enhanced memory for oddball items is long established 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 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 Vancouver 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 environment Schmidt 1991 In the example above people discover 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 generalization and likely plays a central role in our mental development 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 individuals 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 circuits underlying novelty processing see e g Kishiyama Yonelinas Lazzara 2004 Ranganath Rainer 2003 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 Department of Psychology University of Texas at Austin One University Station A8000 Austin TX 78712 e mail yasu psy utexas edu or love psy utexas edu Web site love psy utexas edu Copyright 2006 Psychonomic Society Inc Despite the widespread interest in novelty effects the basis for these effects is not well understood Earlier explanations 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 isolated 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 account deviant items are better remembered when they are more dissimilar to other items Highly dissimilar items occupy an isolated region in a representational space Busey Tunnicliff 1999 and do not activate many stored items during retrieval Nairne 2006 The isolation account attributes 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 memory Sakamoto Love 2004 Interitem similarity relations play opposing roles in these two accounts In the differentiation 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 effects to finer grained memory traces resulting from an 474 enhanced oddball memory through differentiation 475 Differentiation Isolation Figure 1 Examples of differentiation and isolation The top oc tagon is more differentiated whereas the bottom octagon is more isolated item s contrast with highly similar items that establish a context In support of the differentiation account people notice changes in deviant items more accurately Goodman 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 isolated 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 differentiated 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 differentiation 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 advantages As the differentiation account predicts finergrained memory traces result for deviant items that are similar to other items As the isolation account predicts deviant items that are dissimilar to other items are better identified The results from two experiments resolve
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