Why we remember (and how to remember better)

Series:
Speaker: Charan Ranganath
Title: Why we remember (and how to remember better)

(Note: I have only linked the references - I still need to read through the papers and reports.)

Key takeaways:

• It is completely natural to forget most of what we read, watch, learn, or consume. Hermann Ebbinghaus showed that memory retention declines exponentially, with only 20% of the information retained after 9 hours. So, only 1/5 (or less) of information is actually committed to long-term memory (forgetting curve).
• Memory is stored as a low-dimensional representation of synaptic weights. Similarity, in low dimensions, is hard to separate, making it challenging to properly separate similar inputs (situations, faces, etc.). The talk describes a few dimensions that are important for memory storage and retrieval.
  • There are some important points raised in the descriptions of these dimensions (more in notes).
  • Prediction and testing, through retrieval, is important for strengthening memory.
  • Curiosity seems to put the brain in an enhanced learning state.
• Retrieving memory is an act of imagination. One needs to connect the dots in order to fill in the gaps and bring back the memory.
• Retrieving memory also changes the memory itself. Connecting the dots consistently in different ways (than what happened) modifies the dots themselves.

Notes

MEDIC - a mnemonic to understand how memory is stored. It stands for:
M - Meaning
E - Error
D - Distinctiveness
I - Importance
C - Context

Meaning is one of the dimensions of memory. Elements of episodic memory with specific meaning are stored better and can be pulled out of a group of similar memories.

Error - synaptic strengthening (and stronger memory) requires prediction + testing. Retrieval, especially after prediction, is a crucial way of strengthening memory.

• Surprisingly, predicting and validating memories helps strengthen related memories in addition to the retrieved memory.
• Recalling something allowed for better learning than just going over the material again and again (Jonker et al, 2018).

Distinctiveness - Similarity of the memory with other stored forms of memory. Lower the distinctiveness, harder for the memory to form/retrieve.

• Taking pictures/videos on the phone makes an event less distinctive (because recording on phone becomes context, more below). Memory requires not just meaning but other cues (context). Photography and videography remove both. This causes blurring of all these memories.
• As an example, the speaker speculated that this is why some people forgot attending Taylor Swift’s Eras concert.

Importance - here, it means emotional importance. Does the memory provoke fear, excitement, desire, love, surprise, or curiosity? These emotions then cause the release of neurotransmitters which help in memory consolidation.

• Curiosity especially seems to help remembering better (Gruber et al, 2014; Gruber et al, 2019).
• Being in a curious state allows getting into an enhanced learning state which allows information to be stored better. This applies to not just the curiosity-inducing information, but also other information (context) to be stored better. And this seems to be consistent and common for all age groups!

Context - The overall background state with respect to the memory of question. This helps store the memory better (and allows for mental time travel).

• Context is important. A lack of context implies memories won’t be stored properly.
• As an example, the speaker talked about his conversations with students during the pandemic. When he asked them how they felt time was progressing, they all said that it was slow on a daily basis but was very fast over weeks and months.
• The reason for this, the speaker speculated, is that students were in the same context (taking courses through video and being inside the house the whole day), so the memories were not stored/retrieved properly. Because of this, over the duration of the weeks, there were not too many distinctive episodic memories, and the perception is that time moves fast.
• I resonate with this as I had (and occasionally feel) this paradoxically feeling of time passing slow during the week and fast over the month (note from a couple of years back: 2023-10-22-is-time-passing-too-quickly).¹

Overall, episodic memory is stored over a low-dimensional space. It requires imagination to connect the dots to bring back the memory. And the act of connecting the dots often changes the dots by itself (i.e retrieving memory, changing the memory).

Another interesting point is that because recalling memory is essentially filling in the blanks, the way the memory is recalled depends on your perspective. The same memory can be retrieved in different ways (i.e the dots can be connected in different ways) depending on the person you are in the “present”.

Footnotes

1. When I read back my note, I was surprised to see that I had pulled out different aspects of the mnemonic (distinctiveness, context, importance, etc.) and indicated that this might be the reason. ↩