Review
Personal semantics: at the crossroads of semantic and episodic memory

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Declarative memory is usually described as consisting of two systems: semantic and episodic memory. Between these two poles, however, may lie a third entity: personal semantics (PS). PS concerns knowledge of one's past. Although typically assumed to be an aspect of semantic memory, it is essentially absent from existing models of knowledge. Furthermore, like episodic memory (EM), PS is idiosyncratically personal (i.e., not culturally-shared). We show that, depending on how it is operationalized, the neural correlates of PS can look more similar to semantic memory, more similar to EM, or dissimilar to both. We consider three different perspectives to better integrate PS into existing models of declarative memory and suggest experimental strategies for disentangling PS from semantic and episodic memory.

Section snippets

PS: an intermediate form of declarative memory?

Declarative memory is typically described as consisting of two systems, EM and semantic memory. EM entails recollecting unique events within their specific spatio-temporal context, imbued with a sense of the self mentally traveling through time to re-experience the original event [1]. By contrast, semantic memory pertains to culturally-shared general knowledge (including facts and vocabulary), detached from its context of acquisition and devoid of any subjective sense of mental time travel 1, 2

When PS appears similar to semantic memory (and dissimilar to EM): autobiographical facts

The most common conceptualization of PS is as a set of autobiographical facts (e.g., ‘Nicholas is the name of my youngest brother.’) in contrast to general knowledge of the world (e.g., ‘Nicholas was a 4th-century saint.’) and EMs of unique events (‘I could see that my brother Nicholas’ hands were shaking during his speech at my wedding’). Autobiographical facts share with EM the notion of personal content. However, in PS this personal content refers to a common organizing theme, whereas in EM

Repeated events

A typical EM concerns a single personal experience, whereas semantic memory is based on the extraction of similarities across many events. PS is sometimes operationalized as intermediate between these two poles: repeated personal experiences (e.g., bringing my brother to school every day; Table 1). For such events, it is assumed that one typically does not remember a single instance, but instead has extracted the common characteristics from the series of similar but separate episodes ([28]; but

When PS appears dissimilar to both GS and EM: self-knowledge

A fourth tradition of work on PS focuses on the self, self-image, and personal identity. For example, Neisser [51] proposed that the conceptual self is the most basic form of self-knowledge, allowing us to reflect on our personal characteristics and attributes (e.g., ‘I am a fast reader, but poor at remembering names’). Similarly, Brewer [32] refers to the self-schema as a ‘cognitive structure that contains generic knowledge about the self’. Self-knowledge has most often been operationalized as

Concluding remarks

Even though the empirical assessment of PS first began 30 years ago [4], this field is still in its infancy. Up to the present, the study of PS has largely been restricted to the autobiographical memory literature, as PS is typically not included in models of semantic memory or knowledge. The dearth of research on PS may have been due to the assumption made by many researchers that PS is highly similar to, or even synonymous with, GS. Here, we have shown that this is an oversimplification.

Acknowledgments

Preparation of this manuscript was supported by the Heart and Stroke Foundation of Canada Centre for Stroke Recovery, fellowship 23710 from the ‘Fonds de la Recherche en Santé du Québec’ (FRSQ) to L.R., grants A8347 (M.M.) and 341649 (P.S.R.D.) from the Natural Sciences and Engineering Research Council of Canada (NSERC), and grant MOP-62963 (B.L.) from the Canadian Institutes of Health Research (CIHR). We thank Patrick Seymour for his assistance with preparing the figures.

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