Abstract
Diachronic unity is the belief that, despite changes, we are the same person across the lifespan. We propose that diachronic unity is supported by the experience of remembering the self over time during episodic recall (i.e., phenomenological continuity). However, we also predict that diachronic unity is also possible when episodic memory is impaired, as long as the ability to construct life narratives from semantic memory (i.e., semantic continuity) is intact. To examine this prediction, we investigated diachronic unity in Alzheimer's Disease (AD) and amnestic mild cognitive impairment (aMCI), two conditions characterised by disrupted phenomenological continuity. If semantic continuity is also altered in these conditions, there should be an associated deterioration in diachronic unity. Participants with AD, aMCI, and healthy controls (HC) completed a self-persistence interview measuring diachronic unity (beliefs about self-persistence, explanations for stability/change). Semantic continuity was assessed with a life-story interview measuring autobiographical reasoning (self-event connections), and coherence (temporal/thematic/causal) of narratives. Our results highlight a complex relationship between semantic continuity and diachronic unity and revealed a divergence between two aspects of diachronic unity: AD/aMCI groups did not differ from HC in continuity beliefs, but AD explanations for self-persistence were less sophisticated. Semantic continuity was most impaired in AD: their narratives had fewer self-event connections (vs. HCs) and lower temporal/thematic coherence (vs. HC/aMCI), while both AD/aMCI groups had lower causal coherence. Paradoxically AD participants who scored higher on measures of beliefs in the persistence of the core self, provided less sophisticated explanations for their self-persistence and were less able to explore persistence in their life narratives. These findings support the importance of semantic continuity to diachronic unity, but suggest a more nuanced and multifaceted relationship than originally proposed in our model. In AD, diminished life narratives that retain features of cultural life scripts are sufficient for strong subjective beliefs of self-persistence, but not for sophisticated explanations about persistence. Better semantic continuity, with the ability to weave high-quality life narratives, may scaffold the capacity to understand and explain one's diachronic unity, but this produces less surety about self-persistence.
Highlights
Interviewer: Do you feel that you are the same person as you were when you were in your early 20s? Participant: Yes, oh yes! I don’t know, I don’t know why
We investigated diachronic unity in Alzheimer’s Disease (AD) and amnestic mild cognitive impairment, two conditions characterised by disrupted phenomenological continuity
This study provides some important insights for our model of how autobiographical memory (AM) supports diachronic unity by examining whether semantic continuity can provide a sense of self persistence in disorders where AM deficits disrupt phenomenological continuity (Prebble et al, 2013)
Summary
Interviewer: Do you feel that you are the same person as you were when you were in your early 20s? Participant: Yes, oh yes! I don’t know, I don’t know why. - Extract from self persistence interview (Participant 010b from AD group, MMSE = 10). The act of remembering oneself in the past instantly links the present individual to their past self: mentally, emotionally, and experientially. Just as I can know that my current experiences are my own because my subjective experience tags them as such, so too I can know that my episodically remembered past was experienced by “me.” This sentiment is clearly articulated in Locke (1964/1970) claim about the relationship between consciousness and identity: “as far as this consciousness can be extended backwards to any past action or thought, so far reaches the identity of that person; it is the same self it was ; and it is by the same self with this present one that reflects on it, that that action was done.” Just as I can know that my current experiences are my own because my subjective experience tags them as such, so too I can know that my episodically remembered past was experienced by “me.” This sentiment is clearly articulated in Locke (1964/1970) claim about the relationship between consciousness and identity: “as far as this consciousness can be extended backwards to any past action or thought, so far reaches the identity of that person; it is the same self it was ; and it is by the same self with this present one that reflects on it, that that action was done.” (p. 181)
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