Much has been written on the wonders of human memory: the astounding feats of recall, the way memories shape our identity and are shaped by them, memory as a literary theme and a historical one. But what of forgetting? This is the topic of a new book by Douwe Draaisma, author of The Nostalgia Factory and a professor of the history of psychology at the University of Groningen. In Forgetting, Draaisma considers dreaming, amnesia, dementia and all of the ways that our minds — and lives — are shaped by memory’s opposite. He answered questions from Mind Matters editor Gareth Cook.

What is your earliest memory and why, do you suppose, have you not forgotten it? 
Quite a few early memories in the Netherlands involve bicycles, and mine is no exception. I was two-and-a-half years old when my aunts walked my mother to the train station. They had taken a bike along to transport her bags. I was sitting on the back of the bike. Suddenly the whole procession came to a halt when my foot got caught between the spokes. I’m pretty sure this memory is accurate, since I had to see a doctor and there is a dated medical record. It’s a brief, snapshot-like memory, black-and-white. I don’t remember any pain, but I do remember the consternation among my mom and her sisters.

Looking back on this memory from a professional perspective, I would say that it has the flash-like character typical for first memories from before age 3; ‘later’ first memories are usually a bit longer and more elaborate. It also fits the pattern of being about pain and danger. Roughly three in four first memories are associated with negative emotions. This may have an evolutionary origin: I never again had my foot between the spokes. And neither have any of my children.

"Forgetting" is usually thought about in a negative sense but you come to it with a different perspective. Can you explain how you arrived at this way of thinking? 
Psychologist Endel Tulving once counted how many different types of memory there are and he came up with a staggering figure of 256, each with their own laws of encoding, retention, reproduction, and so on. Then it dawned on me that there must also be a multitude of types of forgetting. Considering that we forget so much more than we remember, it is fair to say that the core business of memory is forgetting. After the switch, the topics came in swift procession. Why is it that your colleague remembers your idea, but seems to have forgotten that it was your idea? Why do portraits tend to eclipse our memories of faces? Why is there an art of memory, but no art of forgetting? See?

Why does a colleague remember an idea, but not whose idea it was?
This phenomenon is actually a nice demonstration of the fact that we should think of ‘memory’ as a federation of different types of memory. Suppose you’re in a meeting with colleagues, discussing some problem. You come up with a suggestion, but is is decided someone else’s solution will be tried first. This situation activates two types of memories. Autobiographical memory takes care of retaining who was there, whether it was a morning or an afternoon meeting, perhaps even what the weather was like that day. Semantic memory retains the facts of the matter: what the problem was, which solutions were suggested, etc. The trouble is, semantic memory has trouble remembering sources and circumstances. Most of the facts you remember – such as the meaning of ‘incubation’ or the capital of Sweden – are just the facts, and you have probably forgotten who told you or where you read this. A week later, at a follow-up of the meeting, you may find that your colleague has retained your idea, thanks to his wonderful semantic memory, but has forgotten its source – you.

And, tell me what an “art of forgetting” might look like — why would that be useful, and what might some of its techniques be?
Sadly, or perhaps fortunately, there is no such a thing as deliberate forgetting. Rather the reverse, we seem to have a very tenacious type of memory for the things we would gladly forget, such as childhood humiliations, embarrassing situations or scenes you had rather not witnessed. But even if there were some technique of forgetting, of editing at will what you remember or forget, most people tell me they would hesitate to do so. Consider the movie Eternal Sunshine on a Spotless Mind, which is a profound thought experiment on the averse consequences of deliberate forgetting. In the movie, Clementine and Joel were in a loving relationship when things turned sour. Clementine ends the relation and, moreover, wants to get him out of her memory as well. It then turns out that there is an obscure medical company, Lacuna Inc (!), specialized in erasing memories no longer wanted. Soon Joel has disappeared from her memory. On learning this, Joel wants the same treatment to get her out of his memory. At this point you may already sense the tenor of the story. They meet again, fall in love again, and again the relationship fails. Without painful memories you may find yourself repeating painful situations. So, not being able to forget what you dearly would like to forget may actually be a blessing in disguise.

What light do dreams shed on how and why we forget? 
Waking from a dream and then trying to remember it is much like watching the movie Memento: you try to grasp a story that is told in reverse chronological order. After all, you wake up with the final scene of the dream-story, and then try to remember what led up to this final scene. Julius Nelson, an American biologist, pointed this out in 1888. Reconstructing the dream-story means hunting it down till you finally reach the beginning. And since this is a time-consuming and elaborate process you will often find that the beginning of the dream  is forgotten before you get there. To me, this demonstrates that our memory operates best with stories in their natural chronology, where you have causes and questions first and consequences and answers later.

I wonder, do you see any connection between forgetting and sleepwalking, where someone wakes up, but fails to forget the dream in some sense?
The paradox of sleepwalking is that we do this during ‘deep sleep’, not during ‘rem-sleep’, when we are close to waking. Most of the dreams we remember are dreamt during rem-sleep. During deep sleep there is hardly any recollection of dreams, either because we dream less or because we are too far away from a conscious state to remember them. That is probably why people who are sleepwalking seldom remember having been sleepwalking as a result of some dream. If there was a dream at all, it is usually remembered in an extremely sketchy way, such as ‘something with a tomato cage’ (as in the YouTube-hit ‘My mom sleepwalking’).