A general theory of retrieval from long-term memory combines features of associative network models and random search models. It posits cue-dependent probabilistic sampling and recovery from an associative network, but the network is specified as a retrieval structure rather than a storage structure. The theory is labeled SAM, meaning Search of Associative Memory. A quantitative simulation of SAM is developed and applied to the part-list cuing paradigm. When free recall of a list of words is cued by a random subset of words from that list, the probability of recalling one of the remaining words is less than if no cues are provided at all. SAM predicts this effect in all its variations by making extensive use of interword associations in retrieval, a process that previous theorizing has dismissed.

A new model for interference and forgetting is presented. The model is based on the Raaijmakers and Shiffrin search of associative memory (SAM) theory for retrieval from long-term memory. It includes a contextual fluctuation process that enables it to handle time-dependent changes in retrieval strengths. That is, the contextual retrieval strength is assumed to be proportional to the overlap between the contextual elements encoded in the memory trace and the elements active at the time of testing. It is shown that the model predicts a large number of phenomena from the classical interference literature. These include the basic results concerning retroactive inhibition, proactive inhibition, spontaneous recovery, independence of List 1 and List 2 recall, Osgood's transfer and retroaction surface, simple forgetting functions, the use of recognition measures, and the relation between response accuracy and response latency. It is shown that these results can be explained by a model that does not incorporate an "unlearning" assumption, thus avoiding many of the difficulties that have plagued the traditional interference theories.

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Lesion studies have shown convincingly that the medial temporal lobes (MTL) and frontal lobes are critical to episodic memory. Ageing generally has been found to have a generally negative effect on episodic memory performance, which might relate to neurofunctional changes in the frontal and medial temporal brain regions. In the present study, we used functional MRI (fMRI) to investigate separately the contributions of encoding and retrieval to the age-related decline in memory. To this end, we compared brain activity patterns obtained during incidental encoding (pleasant/unpleasant judgements about nouns) and subsequent retrieval (recognition) in three groups: a group of young subjects, a group of elderly subjects showing reduced memory performance (ELD-RED), and a group of elderly subjects who still performed in the normal range (ELD-NORM). This allowed us to differentiate between age-related changes in brain activity that affect memory function and those that do not have an apparent effect on memory function, because they are found in both elderly groups. Contrary to previous imaging studies on this topic, we used (self-paced) event-related fMRI to control for differences in performance level across groups by including correct responses only. Comparing the encoding of successfully remembered items with baseline (press left/press right), the young subjects showed a significant increase in brain activation in the left anterior MTL compared with the ELD-RED but not the ELD-NORM subjects. Comparing correctly rejected items (retrieval attempt) with baseline, the ELD-RED group showed much increased overall activity throughout the brain compared with the other groups. However, when correctly recognized items (retrieval attempt + success) were compared directly with correctly rejected items (retrieval attempt), these differences were greatly reduced, revealing common activity in the left parietal, retrosplenial and left anterior prefrontal regions. Therefore, we conclude that the reduced performance in the ELD-RED group is likely to be due to MTL dysfunction during encoding. The differences observed during retrieval attempts may reflect strategic differences. The lack of differences observed in relation to retrieval success suggests that ageing does not affect the processes that support the actual recovery of information.

Spacing between study trials of an item increases the probability that item will be recalled. This article presents a new model for spacing based on the SAM theory of memory developed by Raaijmakers and Shiffrin (1980, 1981). The model is a generalization of the SAM model as applied to interference paradigms (Mensink & Raaijmakers, 1988, 1989 and may be viewed as a mathematical version of the Component-Levels theory proposed by Glenberg (1979). It is assumed that on a second presentation of an item, information is added to an existing trace if the episodic memory image corresponding to that item is retrieved. If it is not retrieved, a new image is stored. It is shown that the model predicts many standard findings including the lack of a spacing effect for the recall of at least one of two items each presented once (Ross & Landauer, 1978).

We propose a sampling-based Bayesian t test that allows researchers to quantify the statistical evidence in favor of the null hypothesis. This Savage-Dickey (SD) t test is inspired by the Jeffreys-Zellner-Siow (JZS) t test recently proposed by Rouder, Speckman, Sun, Morey, and Iverson (2009)

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