The dissertation includes 10 published papers presenting the results of 29 experiments. The following theses mainly based on the results and the conclusion of these publications.
Thesis 1: The concept of ‘episodic inhibition’ proposes that knowledge in episodic memories preserves a pattern of activation/inhibition derived from the original experience or generated in it by subsequent access of memory details. Thus, an item inhibited in episodic memory may nonetheless be activated in a conceptual knowledge structure.
Thesis 2: Here it is proposed that target items following an intentional forgetting procedure represented in an episodic memory of the study phase are marked as to-be-forgotten, and these episodic representations are specifically tagged not to be recollectively experienced.
Thesis 3: If people observe another person with the same intention to learn, and see that this person is instructed to forget previously studied information, then they will produce the same intentional forgetting effect as the person they observed. This seems to be an important aspect of human learning: if we can understand the goal of an observed person and this is in line with our behavioural goals then our learning performance will mirror the learning performance of the model. Our results support the assumption that suppression of episodic memories is not automatically generated by environmental cues but depends on the goals of the person who encodes and retrieves them.
Thesis 4: Our results indicate that possible disrupted executive functions (e.g. in schizophrenia) considerably weaken the ability of patients to intentionally avoid recent memories. This can occur even when other incidentally initiated inhibitory processes appear to function relatively normally.
Thesis 5: Retrieving memories does not induce forgetting of related memories among participants with obsessive-compulsive disorder (OCD). Lack of forgetting in OCD occurred in spite of the fact that overall memory and the mnemonic effect of practicing memories was almost identical to that among healthy controls. Our results suggest that suppression of irrelevant, interfering memories during competitive recall is impaired in OCD. The lack of
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retrieval-induced forgetting (RIF) among OCD patients is not related to overall recall performance, rather, we suggest that it is related to differences in resolving interference during competitive retrieval.
Thesis 6: It is proposed that RIF occurs only when interference during competitive retrieval reaches moderate levels, but not when it is too low or too high. This proposal indicates that low levels of interference do not trigger interference resolution, whereas interference resolution can fail when the interference reaches extremely high levels.
Thesis 7: An initial retrieval of the learning set shields against the adverse effect of retrieval practice; RIF is absent either when measured in comparison to baseline performance on the initial retrieval or to members of unpracticed categories. Here it is proposed that retrieval is the key process that enhances long-term accessibility of retrieved memories and it is the process that can hinder retrieval of items through search set restriction or can shield against the adverse effect of later selective retrieval.
Thesis 8: Here a revised form of the episodic inhibition account is proposed: retrieval practice establishes a pattern of activation and inhibition over the contents or features of an episodic memory of the study phase. As the episodic memory is consolidated in long-term memory, the pattern of activation and inhibition, which determines the accessibility of the contents of the memory, stabilizes and becomes resistant to further change. As a memory is repeatedly retrieved and its contents are accessed, its durability in long-term memory increases, and the accessibility levels of its contents become fixed. Our findings suggest that sleep is important to this process of consolidation. It is proposed that consolidation processes occurring during sleep, and possibly featuring some form of offline rehearsal, mediate these long-term effects of retrieval practice.
Thesis 9: Here it is proposed that recalling two associated items can be simultaneously attenuated or primed depending on how the association is accessed. Furthermore, not thinking about a target item, as compared with thinking about an alternative, can produce the same decrements in cued recall or, sometimes, differences. Our findings suggest that the locus of inhibition in the Think/No-think Task (TNT) task is not the representation of the items themselves in memory but, rather, the associations between them and, in particular, the A→ B association.
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Thesis 10: Based on the results of a functional neuroimaging study it is proposed that the long-term behavioral advantage of repeated retrieval over repeated study is due to the differential activation of a large network. Specifically, when the retention interval is long, participants cannot effectively process the cue and a large percentage of retrieval attempts fail. Thus, the so-called testing effect may be a consequence of processes that, through each additional retrieval act, conserve the effectiveness of the retrieval cue to access a specific memory. Based on our findings, we suggest that this strengthening arises from an effective and stable response for specific episodic cues in a network of brain areas related to cognitive control functions.
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