A classic example of how alternative framing can change the emotional impact of a number is an advertisement that appeared on the London Underground in 2011, proclaiming that ‘99% of young Londoners do not commit serious youth violence’. These ads were presumably intended to reassure passengers about their city, but we could reverse its emotional impact with two simple changes. First, the statement means that 1% of Londoners do commit serious violence. Second, since the population of London is around 9 million, there are around 1 million people aged between 15 and 25, and if we consider these as ‘young’, this means there are 1% of 1 million or a total of 10,000 seriously violent young people in the city. This does not sound at all reassuring. Note the two tricks used to manipulate the impact of this statistic: convert from a positive to a negative frame, and then turn a percentage into actual numbers of people.
It’s not just repeated physical actions that can rewire our brains. Purely mental activity can also alter our neural circuitry, sometimes in far-reaching ways. In the late 1990s, a group of British researchers scanned the brains of sixteen London cab drivers who had between two and forty-two years of experience behind the wheel. When they compared the scans with those of a control group, they found that the taxi drivers’ posterior hippocampus, a part of the brain that plays a key role in storing spatial representation won much larger than normal.