Human memory does not operate like a video tape that can be rewound and rewatched, with every viewing revealing the same events in the same order. In fact, memories are reconstructed every time we recall them. Aspects of the memory can be altered, added or deleted altogether with each new recollection. This can lead to the phenomenon of false memory, where people have clear memories of an event that they never experienced.

False memory is surprisingly common, but a number of factors can increase its frequency. Recent research in my lab shows that being very interested in a topic can make you twice as likely to experience a false memory about that topic.

Previous research has indicated that experts in a few clearly defined fields, such as investments and American football, might be more likely to experience false memory in relation to their areas of expertise. Opinion as to the cause of this effect is divided. Some researchers have suggested that greater knowledge makes a person more likely to incorrectly recognise new information that is similar to previously experienced information. Another interpretation suggests that experts feel that they should know everything about their topic of expertise. According to this account, experts’ sense of accountability for their judgements causes them to “fill in the gaps” in their knowledge with plausible, but false, information.

To further investigate this, we asked 489 participants to rank seven topics from most to least interesting. The topics we used were football, politics, business, technology, film, science and pop music. The participants were then asked if they remembered the events described in four news items about the topic they selected as the most interesting, and four items about the topic selected as least interesting. In each case, three of the events depicted had really happened and one was fictional.

The results showed that being interested in a topic increased the frequency of accurate memories relating to that topic. Critically, it also increased the number of false memories – 25% of people experienced a false memory in relation to an interesting topic, compared with 10% in relation to a less interesting topic. Importantly, our participants were not asked to identify themselves as experts, and did not get to choose which topics they would answer questions about. This means that the increase in false memories is unlikely to be due to a sense of accountability for judgements about a specialist topic.

A possible explanation

Our interpretation of our results supports the theory that false memories arise as a side-effect of the mechanisms underlying true memories. Briefly, the more a person knows about a topic, the more memories relating to that topic are stored in their brain. When new information about that topic is encountered, it may trigger similar memory traces that are already stored. This can result in a sense of familiarity or recognition of the new material, which in turn leads to the conviction that the information has been encountered before, and is in fact an existing memory.

Here’s an example: imagine you are very interested in polar bears. You read wildlife magazines, watch nature documentaries and subscribe to real-time video streams of polar bears in the wild. One day, a friend tells you about a news article they read last year describing a polar bear getting caught in a trawler’s fishing net. Despite the fact that you have never heard this story before, it triggers associated memories about polar bears being endangered and concerns about arctic trawling. The story feels familiar, so you become convinced that you remember hearing about the event at the time. The more information you have about the topic, the more likely it is that new information will trigger old, associated memories.

Our research has implications for the way we think about memory. Most people are fairly confident in their own memory for events, but false memory is a lot more frequent than they realise. Counter-intuitively, our results suggest that while being interested in something does make you more knowledgeable, these memories may not always be reliable.