Worm holes in memory: Is memory one representation or many?

Worm holes in memory: Is memory one representation or many? Dirk U. Wulff (Wulff@mpib-berlin.mpg.de) Max-Planck-Institute for Human Development, Lentzeallee 94, 14195 Berlin, Germany Thomas T. Hills (T.T.Hills@warwick.co.uk) Department of Psychology, University of Warwick Coventry CV4 7AL, UK Ralph Hertwig (Hertwig@mpib-berlin.mpg.de) Max-Planck-Institute for Human Development, Lentzeallee 94, 14195 Berlin, Germany Abstract The analogy of space to human cognition has a long- standing tradition. Our study aims to elaborate on the validity of this analogy for search in memory. Using the search of associative memory framework (SAM) we show that people are able to dynamically recruit independent memory representations in the recall of country names. By instructing participants to use specific recall cues we also show that despite a strong effect on the retrieval sequence, total recall from memory remains unaffected. Whereas these findings strongly support a higher dimensionality to memory than often assumed, the simultaneous finding of severe retrieval time costs for non-default representations suggests that the use of particular retrieval structures may be adaptive. In sum, our results support local-to-global memory search strategies similar to foraging strategies in space, but further suggest that memory is not constrained to one local representation, but may indeed support many. Keywords: Free recall; verbal fluency task; memory representation; Search of Associative Memory (SAM). Introduction Memory has long been considered to represent a high- dimensional landscape over which we search for information. The recent proliferation of semantic space models, which acquire semantic similarity of words based on statistical processing of text corpora implicitly characterizes memory as embodying such a representation. This idea is not new. In his “Principles of Psychology” William James wrote “We make search in memory . just as we rummage our house for a lost object“ (1890, p. 654), suggesting that search in memory is comparable to search in space. But how comparable is it? Research on spatial imagery and cognitive maps suggests that mental operations share much in common with the way we move around the physical world (e.g. Kosslyn, Ball, and Reiser, 1978). Almost all models of long-term memory incorporate a dimension of similarity (inverse of distance) in order to explain priming and serial position effects (e.g. Anderson, & Pirolli, 1984; Brown, Neath, & Chater, 2007). Shepherd’s account of distance in mental representations (Shepard, & Metzler, 1971), as well as models of categorization (e.g. Nosofsky, 1988), suggests a similar conceptual landscape, in which similar items reside near one another and less similar items reside further apart. Underlying these approaches is an implicit assumption, one that is highlighted by James. If searching memory is like rummaging our house for a lost object, is there just one house (i.e., representation) or are there many? Could an item be in more than one representation, and if so, does one representation facilitate memory search better than another? If memories reside in multiple representations, this presents a problem for many existing models of knowledge representation—that is, especially those that produce but one representation. Moreover, multiple representations would exemplify a feature of memory that clearly separates memory from space: outside of wormholes, the only way to get from one point in space to another is to travel the distance between them. Memory, on the other hand, may have no such constraints. Before we describe how we investigated the possibility of multiple memory representations, we first describe some of the previous research that has highlighted the relationship between memory and space. Memory and Space Following this analogy between space and memory, Hills and colleagues recently put forth a model wherein free recall from memory produces patterns that can be predicted by a classical theorem of optimal foraging theory, the marginal value theorem (Hills, Jones, Todd, 2012). This theory describes optimal switching between explorative and exploitative search in response to a patchy resource environments. Further supporting the notion that internal search may be similar to external search in space, Hills, Todd, and Goldstone (2008) found that priming search in space primes search in a lexical search task, suggesting that a shared cognitive process may search in both domains.