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Many countries have made it illegal to chat into a hand-held mobile phone while driving. But the latest research further confirms that the danger lies less in what a motorist’s hands do when he takes a call than in what the conversation does to his brain. Even using a “hands-free” device can divert a driver’s attention to an alarming extent. Melina Kunar of the University of Warwick, and Todd Horowitz of the Harvard Medical School ran a series of experiments in which two groups of volunteers had to pay attention and respond to a series of moving tasks on a computer screen that were reckoned equivalent in difficulty to driving. One group was left undistracted while the other had to engage in a conversation using a speakerphone. As Kunar and Horowitz report, those who were making the equivalent of a hands-free call had an average reaction time 212 milliseconds slower than those who were not. That, they calculate, would add 5.7 metres to the braking distance of a car travelling at 100kph. They also found that the group using the hands-free kit made 83% more errors in their tasks than those who were not talking. To try to understand more about why this was, they tried two further tests. In one, members of a group were asked simply to repeat words spoken by the caller. In the other, they had to think of a word that began with the last letter of the word they had just heard. Those only repeating words performed the same as those with no distraction, but those with the more complicated task showed even worse reaction times—an average of 480 milliseconds extra delay. This shows that when people have to consider the information they hear carefully, it can impair their driving ability significantly. Punishing people for using hand-held gadgets while driving is difficult enough, even though they can be seen from outside the car. Persuading people to switch their phones off altogether when they get behind the wheel might be the only answer. Who knows, they might even come to enjoy not having to take calls. In the experiments, the two groups of volunteers were asked to handle a series of moving tasks which were considered .（）

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