Metric and chronological time in human episodic memory
Tor Ivar Hansen
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Abstract
The relative contributions of metric and chronological time in the encoding of episodic memories are unknown. One hundred one healthy young adults viewed 48 unique episodes of visual events and were later tested on recall of the order of events (chronological time) and the precise timing of events (metric time). The behavioral results show that metric recall accuracy correlates with chronological accuracy for events within episodes, but does not play a role on larger time-scales across episodes. Functional magnetic resonance imaging during encoding and recall showed that metric time was represented in the posterior medial entorhinal cortex, as well as the temporal pole and the cerebellum, whereas chronological time was represented in a widespread brain network including the anterior lateral entorhinal cortex, hippocampus, parahippocampal cortex and the prefrontal cortex. We conclude that metric time has a role in episodic memory on short time-scales and is mainly subserved by medial...
Key takeaways
- While mental representation of chronological time preserves the temporal order in which life events occur, it does not itself contain precise information about the timing of events, or "metric time" [3][4][5] .
- Importantly, the experimental paradigm described here affords exploration of all aspects of temporal representation within the context of episodic memories, in contrast to previous studies which limited the analyses to one, or a few, temporal measures 3, 5, 12-15, 22-24 . (1.1) Role of metric time: Metric time is only encoded within episodes To evaluate whether the mental representations of metric time and chronological time were accurate, both within episodes and between episodes, we compared the distribution of the participant's responses with a shuffled distribution ( Figure 2, and see Methods).
- From the Episode test, we obtained metric accuracy between episodes (Metric timeM2) ( Figure 1g).
- Chronological time between episodes or Episode orderc2 was estimated by calculating, for each episode, how far away the recalled episode sequence position was from the correct position in the Episode test ( Figure 1g).
- The first model was used to investigate Metric timeM1, Event orderC1, Episode orderC2, Chronological timeC3, and the second was used to investigate Object recognition.
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