Your Past is Not Your Own

September 22, 2016

When we think of our memories, it’s natural to imagine a kind of personal library, a bit like Sherlock Holmes’s memory palace, where we have stored the most precious events of our lives. Along the shelves, you can pull out that fifth birthday when you dressed up as Superman, or that family picnic when you found a worm in your sandwich.

Good and bad, these events define who we are; it’s the reason that amnesia is so scary. We certainly wouldn’t want anyone else interfering with those intimate recollections, or we would risk losing a vital part of our selves.

Except it turns out that your friends, family and colleagues are already ransacking your memory palace. They are rearranging the books on the shelves; they are tearing out pages and scattering them on the floor, or they are scribbling over our most precious volumes. “Our memories are constantly being reshaped by social interactions,” says William Hirst at the New School for Social Research in New York. “People can implant memories, people can induce you to forget or they can reinforce other memories.”

These are not rare events. Every time you have a conversation, you are inviting someone to ghost-write bits of your autobiography. It sounds troubling and it may cause you to rethink everything you thought you knew about your past – yet you may be relieved to discover that there are also some unexpected benefits.

It takes only a second’s thought to realise that memory is rarely a solitary activity. During a day at work, for instance, we will deliberately recall events to tell our partner in the evening; we may even rehearse and refine the story on the train journey home. We will also recall and reminisce for the sake of nostalgia alone – even if the events are long in the past and familiar to everyone concerned. “I don’t know of any other species that does that,” says Hirst. “You can think of bees conveying where the pollen is, but it is very limited – there’s no intention behind it and they are only conveying new information.”

When Hirst first began this research more than a decade ago, he was among just a handful of people examining the ways those interactions change our memories. But times have changed, and it is now becoming clear that social networks can mould and sculpt our minds in profound ways.

1. Collaborative inhibition

Let’s first consider a phenomenon known as “collaborative inhibition”. Imagine that you and your friends John and Jane attended a football match, where you see a fight break out between the two sides. Afterwards, the three of you get together to discuss the event. You may expect that you will each trigger each other’s recall, helping each person to get a better understanding of the event. Although the group as a whole may record more than any single person, each individual will find that their own memory has been slightly impaired by the discussion.

It’s all down to the subtle dynamics of the conversation. If John is particularly talkative, for instance, everyone will be paying attention to his point of view, leading their memories down one avenue while distracting them from their own path. Jane might have been more likely to think about different players from a different team, for instance, or she might have noticed an unusual disturbance in the crowd – but John’s reminders have caused her to lose that train of thought. “John is essentially inhibiting Jane’s ability to remember with full potential,” says Hirst. For this reason, you would gather more details of the event if each person had sat down quietly and recorded all that they had known, before sharing notes afterwards.

2. Shared forgetting

Importantly, the effects of our conversations can linger into our long-term memory. Hirst’s own research has focussed on a phenomenon known as “socially-shared retrieval-induced forgetting”. Through subtleties in the way he talks about an event, John can encourage Jane to forget something over time.

It hinges on the fact that whenever we reactivate a memory, it becomes fragile and malleable. Suppose John is talking about a wedding he attended with Jane. He might mention his speech – reinforcing the memory – but he might neglect to mention a fight on the dancefloor. Through association, this memory may still have been activated at the cellular level (rendering it vulnerable) but Jane may have suppressed that thought to concentrate on the rest of John’s anecdote. As a result, that “silence” has altered the brain’s memory trace, so that Jane will find it harder to retrieve details in the future.

So if you want someone to forget something, the trick is to pick a subject that will activate the memory, while then distracting the person from the crucial detail you would prefer to ignore. Over time, it may then fade.

Hirst has investigated the phenomenon extensively and it appears to be remarkably persistent. In one experiment, for instance, Hirst and his colleague Alin Coman asked pairs of participants to discuss 9/11. The participants did not know each other previously, but they still found that the conversation could still subtly nudge people to forget certain details.

If John forgot to mention the time of day, for instance, Jane would also be less likely to bring up the fact from her own story at a later point. Again, this probably works through activation through association, and suppression. John has triggered the memory in Jane’s mind, and by inhibiting that detail, she later forgets it.

Hirst says that people are often surprised by his work. Surely people would realise that certain details are being neglected, and fight against it? In reality, it rarely happens. “I think it requires a great deal of effort – you have to be really motivated to go beyond what people are talking about,” says Hirst.

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