Memory is difficult to define without being circular. People often define memory as “something you can remember”. But we cannot deny the existence of a memory when there is no recollection.
Sigmund Freud was first to theorise this notion: memories that are not consciously remembered can exert control through the subconscious. Although much of his research methodology is now criticised, Freud opened our eyes on how past events can influence us in ways regardless of our awareness.
So what is memory? I would define memory as “a past that becomes a part of me”. Interestingly, past events can become a part of us in three different ways - as procedural, semantic, and/or episodic memory.
These different ways often occur simultaneously. Learning to ride a bicycle involves procedural memory, in which our bodies remember how to coordinate different limbs and perceptions based on previous attempts at bike riding.
Remembering that gears are used to switch the wheel rotation circumference represents semantic memory.
I can also recall when, where, and with whom I learnt how to ride – an example of episodic memory.
Despite distinctions between the three, all the types of memory appear to undergo similar stages across time. First, attention is critical for the initiation of memory formation. I often lock the door as I am leaving my house without paying attention. Subsequently, at work, I cannot recall whether I have locked my door or not.
This is not due to forgetting, but is a failure in memory formation. It is probably what happened to the police who lost their keys to the Wembley stadium during the recent Olympics.
Attention then leads to working memory, which lasts seconds to minutes. Once an event forms a short- or long-term memory, we are no longer thinking about the event, but retrieval is possible hours to weeks, or months to years, following the event.
Biologically, short- and long-term memories are different from each other, as indicated by the Nobel laureate Eric Kandel’s work.
Long- but not short-term memory involves long-lasting physical changes in neurons that ultimately result in altered levels of electrical and/or chemical communication between different neurons.
Such a biological correlate of memory strongly suggests individual differences in memory abilities. That is, just as our physical abilities are tied to our bodies, our memory abilities are tied to our brains.
On the flip side, we can improve our memory with exercise, just as we can improve our physical abilities with exercise. This makes sense, as the brain is a part of our body.
Nevertheless, the brain is a special and mysterious organ because there exist people with a special ability referred to as “eidetic” or “photographic” memory. Such people display the ability to recall images, words or sounds with extreme precision.
In 2001 the British architectural artist Stephen Wiltshire was filmed flying over London aboard a helicopter and subsequently completing a detailed and perfectly scaled aerial illustration of a four-square-mile area of the British capital within a few hours. It’s a talent he has repeated on several occasions.
In the first half of the 20th century, the Russian mnemonist Solomon Veniaminovich Shereshevsky showed himself capable of recalling strings of random words he had seen decades earlier.
But does eidetic memory exist? Definitely not in the form of the popular misinterpretation of the term that assumes total recall of all events occurring in one’s life.
The only report of such ability comes from Dr Sheldon Cooper from the TV comedy show The Big Bang Theory. In fact, much like any other memory, eidetic memory is affected by factors such as attention, significance, duration/frequency of the event and, most importantly, mnemonic tools.
Shereshevsky reported using a mnemonic technique in which he imagined laying out objects along a stretch of a familiar road during the learning phase.
During the retrieval of those words, he went back and picked them up one by one in his imagination. Such a report proves that his memory was actually highly trained normal memory. Many who claim to have eidetic memory use such mnemonic techniques.
In fact, the existence of eidetic memory as an independent, special memory ability compared to an average person’s memory is very controversial.
Prodigies such as Wiltshire can only retrieve their memory within days, leading some to argue that those cases reflect a form of very strong working or short-term memory.
But there is one extraordinary report of long-term eidetic memory. In 1970, a Harvard vision scientist called Charles Stromeyer published an account in Nature of his subject, Elizabeth.
Elizabeth could recall random dot patterns shown independently to each of her eyes with such precision she could reproduce the 3D image of fused dot patterns even three months after initial exposure to the images.
I urge you not to undermine the credibility of this study due to the fact that Stromeyer married Elizabeth. My bigger concern is how Stromeyer did not attempt any further studies on this incredible result.
Other than this single study, there is no evidence eidetic memory is actually fundamentally different from how an average person acquires, stores and retrieves memory. The difference appears quantitative rather than qualitative.
It is interesting that compared to extreme physical abilities, mental abilities are seen as more extraordinary. People who display eidetic memories are extensively studied in order to understand their beautiful minds. But no-one cares how Usain Bolt runs: in essence, we don’t think he runs differently from us – it’s just we are not that fast.
Whether it is average or special, the subject of memory will continue to fascinate us.
Kuato from the original Total Recall movie stated: “A man is defined by his action not his memory”. But his action will be defined by what he remembers and believes in.
Maybe that’s why scientists are working very hard to understand how memory works. On the other hand, understanding how forgetting happens is rather neglected (I am working on forgetting).
Just as super memory can exist as an extreme form of normal memory, perhaps erasure is also possible as a form of super forgetting.
See more Explainer articles on The Conversation.