The authors present the context maintenance and retrieval (CMR) model of memory search, a generalized version of the temporal context model of M. W. Howard and M. J. Kahana (2002a) , which proposes that memory search is driven by an internally maintained context representation composed of stimulus-related and source-related features. In the CMR model, organizational effects (the tendency for related items to cluster during the recall sequence) arise as a consequence of associations between active context elements and features of the studied material. Semantic clustering is due to longstanding context-to-item associations, whereas temporal clustering and source clustering are both due to associations formed during the study episode. A behavioral investigation of the three forms of organization provides data to constrain the CMR model, revealing interactions between the organizational factors. Finally, the authors discuss the implications of CMR for their understanding of a broad class of episodic memory phenomena and suggest ways in which this theory may guide exploration of the neural correlates of memory search. Keywords: context, organization theory, source, encoding task, computational model The free-recall paradigm has had an important role in the development of theories of memory search, and research in this domain has tended to follow two threads. The first deals with organization; the free-recall paradigm reveals structure and organization in memory through the ways items tend to cluster in recall sequences (for a review, see Puff, 1979) . When items are recalled successively, it indicates that they are somehow related or structurally connected in the memory system. The second thread deals more directly with the memorability or availability of individual items in memory, often in terms of the sort of processing the item received. In these studies, theoretical attention focuses on whether particular items were recalled and not on the order of those recalls. These studies have dominated the recent literature and tend to employ a variant of the free-recall paradigm designed to minimize organizational influences, through the use of a single trial and randomly chosen items (Battig & Bellezza, 1979) . However, recent work has shown that even in the single-trial free-recall paradigm, one can see substantial and reliable organizational influences, both in terms of the temporal contiguity of successively recalled items (Kahana, 1996) and in terms of the semantic relatedness of the studied items (Howard & Kahana, 2002b) . Models of the free-recall paradigm have tended to ignore order information as a simplifying assumption (Brown, Neath, & Chater, 2007; Wixted & Rohrer, 1993) . However, a recent trend in the modeling literature has brought these organizational principles to center stage. The temporal context model (TCM) of Howard and Kahana (2002a) is a formal computational model of the human memory system designed to explain the phenomena of temporal organization. By this model, a slowly changing internal context representation is associated with each of the studied items and is then used to guide memory search. TCM is a model of the interactions between context and content, but it lacks the machinery to explain the important role of nontemporal factors in memory retrieval, such as semantic and source information (e.g., Howard & Kahana, 2002b; Hintzman, Block, & Inskeep, 1972) . We generalize TCM to model the semantic similarity relations between words, as well as the influence of source context on the recall process. We refer to this generalized model as the context maintenance and retrieval (CMR) model. According to the CMR model, the most obvious behavioral manifestation of organization is the clustering of recalled items along a dimension of similarity. This similarity may arise because of the longstanding associative relations between studied items (giving rise to semantic organization), or
Polyn REF discussed the free recall process and reported the retrieval maintenance.
A context maintenance and retrieval model of organizational processes in free recall
Psychological Review
Psychology Medicine