Unintentional forgetting is beyond cognitive control

Highly Superior Autobiographical Memory (HSAM): A Systematic Review

Individuals possessing a Highly Superior Autobiographical Memory (HSAM) demonstrate an exceptional ability to recall their own past, excelling most when dates from their lifetime are used as retrieval cues. Fully understanding how neurocognitive mechanisms support exceptional memory could lead to benefits in areas of healthcare in which memory plays a central role and in legal fields reliant on witnesses' memories. Predominantly due to the rareness of the phenomenon, existing HSAM literature is highly heterogenous in its methodologies used. Therefore, following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, we performed the first systematic review on this topic, to collate the existing behavioural, neuroanatomical, and functional HSAM data. Results from the 20 experimental selected studies revealed that HSAM is categorised by rapidly retrieved, detailed and accurate autobiographical memories, and appears to avoid the normal aging process. Functional neuroimaging studies showed HSAM retrieval seems characterised by an intense overactivation of the usual autobiographical memory network, including posterior visual areas (e.g., the precuneus). Structural neuroanatomical differences do not appear to characterise HSAM, but altered hippocampal resting-state connectivity was commonly observed. We discuss theories of HSAM in relation to autobiographical encoding, consolidation, and retrieval, and suggest future directions for this research.

Tracking induced forgetting across both strong and weak memory representations to test competing theories of forgetting

Here we employ a novel analysis to address the question: what causes induced forgetting of pictures? We use baseline memorability as a measure of initial memory strength to ask whether induced forgetting is due to (1) recognition practice damaging the association between the memory representation and the category cue used to activate the representation, (2) the updating of a memory trace by incorporating information about a memory probe presented during recognition practice to the stored trace, (3) inhibitory mechanisms used to resolve the conflict created when correctly selecting the practiced item activates competing exemplars, (4) a global matching model in which repeating some items will hurt memory for other items, or (5) falling into the zone of destruction, where a moderate amount of activation leads to the highest degree of forgetting. None of the accounts of forgetting tested here can comprehensively account for both the novel analyses reported here and previous data using the induced forgetting paradigm. We discuss aspects of forgetting theories that are consistent with the novel analyses and existing data, a potential solution for existing models, proposals for future directions, and considerations when incorporating memorability into models of memory.

What do laboratory-forgetting paradigms tell us about use-inspired forgetting?

Directed forgetting is a laboratory task in which subjects are told to remember some information and forget other information. In directed forgetting tasks, participants are able to exert intentional control over which information they retain in memory and which information they forget. Forgetting in this task appears to be mediated by intentional control of memory states in which executive control mechanisms suppress unwanted information. Recognition-induced forgetting is another laboratory task in which subjects forget information. Recognizing a target memory induces the forgetting of related items stored in memory. Rather than occurring due to volitional control, recognition-induced forgetting is an incidental by-product of activating items in memory. Here we asked whether intentional directed forgetting or unintentional recognition-induced forgetting is a more robust forgetting effect. While there was a correlation between forgetting effects when the same subjects did both tasks, the magnitude of recognition-induced forgetting was larger than the magnitude of directed forgetting. These results point to practical differences in forgetting outcomes between two commonly used laboratory-forgetting paradigms.

Recognition and rejection each induce forgetting

Recognition-induced forgetting, whereby the recognition of targeted memories induces the forgetting of related memories, results from the recognition of old objects and rejection of new objects. Here we asked whether both these tasks are necessary to induce forgetting. Our unique design allowed us to isolate the recognition of old objects from the rejection of new objects by presenting subjects with only new objects, only old objects, and a mixture of both in separate conditions of an old-new recognition task. In all three conditions, we successfully induced forgetting. The magnitude of forgetting was statistically indistinguishable across all three conditions, showing that recognition of old objects and rejection of new objects are each building blocks of forgetting. These findings pinpoint both recognition and rejection as mechanisms underlying recognition-induced forgetting and demonstrate the ubiquity of this forgetting effect.

Recognition-induced forgetting is caused by episodic, not semantic, memory retrieval tasks

Recognition-induced forgetting is a within-category forgetting effect that results from accessing memory representations. Advantages of this paradigm include the possibility of testing the memory of young children using visual objects before they can read, the testing of multiple types of stimuli, and use with animal models. Yet it is unknown whether just episodic memory tasks (Have you seen this before?) or also semantic memory tasks (Is this bigger than a loaf of bread?) will lead to this forgetting effect. This distinction will be critical in establishing a model of recognition-induced forgetting. Here, we implemented a design in which both these tasks were used in the same experiment to determine which was leading to recognition-induced forgetting. We found that episodic memory tasks, but not semantic memory tasks, created within-category forgetting. These results show that the difference-of-Gaussian forgetting function of recognition-induced forgetting is triggered by episodic memory tasks and is not driven by the same underlying memory signal as semantic memory.