Cognitive mechanisms of normal and pathological forgetting

The objectives of this PhD were to investigate forgetting, how to measure forgetting and what are the underlying mechanisms behind this effect. 1. Following the progress of forgetting over time will require repeated testing. There is strong evidence that this may enhance recall, while opposing evidence, from part-set cueing studies suggests that probing one item may reduce the memorability of others within the set. It appears that whenever we test memory, we change it, but how? Experiment 1 and Experiment 2 compare long-term forgetting in healthy younger and older individuals and investigates whether repeated partial testing will enhance long-term memory performance based on the level of semantic coherence or integration of material to be remembered, possibly via a relearning or a priming effect. 2. Some previous studies showed that, under particular experimental conditions, patients suffering from a range of memory deficits (i.e., amnesia) appear to retain what they have learnt as well as controls (Huppert, & Piercy, 1978; 1979; Squire, 1981; Kopelman, 1985; Freed, Corkin & Cohen, 1987; Frisk & Milner, 1990a; 1991; Greene et al., 1995). A challenge to this view comes from a subsample of epileptic patients, who have been found to show accelerated long-term forgetting (ALF), in some cases showing normal learning over a period of 30 minutes to one hour, followed by dramatic loss of information later on (Butler & Zeman, 2008). Whether ALF applies to other patient populations remains to be established. Experiment 3 examines long-term forgetting as well as the effect of repeated partial testing in healthy people and in people with Alzheimer’s Disease (AD). Assessing whether AD patients present with ALF and whether repeated partial testing delays long-term forgetting in both groups. 3. A frequent assumption is that when comparing two groups they should be matched on level of initial learning. At the same time, several influential studies from the early literature suggest that initial degrees of learning do not influence the rate of forgetting in the long-term (e.g., Slamecka & McElree, 1983; Slamecka, 1985). Experiment 4 is a replication of Experiment 1 from Slamecka & McElree’s (1983) classic study. 4. Achieving a particular degree of learning at encoding will require more exposures for lower performing individuals compared to high performing individuals. Therefore, Experiment 5 aimed to examine whether varying the degrees of learning at encoding will differentially affect participants long-term forgetting rate based on their individual learning capacity. 5. An important classification of long-term memory is based on its temporal direction. While retrospective memory (RM) deals with past information, the remembering of future intentions depends on prospective memory (PM). The similarities between these two memory types have been frequently raised, yet an important distinction lies in their evaluation. When we measure RM tasks (in the laboratory) the participant is specifically directed to retrieve information, while when measuring PM tasks, the retrieval of the intended action is self-initiated. Experiment 6 investigated whether the retrieval of an intended PM action would be facilitated if participants repeated back the PM task multiple times at encoding (i.e., learned the PM task more). 6. In everyday life we typically only remember the gist of events that are encountered once and processed incidentally. Similarly, even events that are encountered repeatedly can be processed incidentally, with much of the rich contextual details being forgotten. In the forgetting literature, one class of such repetitive events such as taking medication daily, refer to habitual PM. In habitual PM the necessity of initiating (or not) a certain action is highly dependent on the accurate memory of the previously performed action (Marsh et al., 2007; McDaniel et al., 2009). The aim of Experiment 7 was to examine forgetting of habitual PM tasks and its underlying mechanisms, as well as to devise a method to enhance the memory of previously performed actions in habitual PM