Why do people drive drunk? People know that drunk driving is dangerous. We educate people in school and through public service announcements. Most sober people will tell you that they would not put themselves behind the wheel of a car when impaired. Yet the newspapers report deaths from alcohol-related accidents. It is hard to go a week without reading about a high-profile athlete or politician who has been arrested for drunk driving.

How does this happen?

A paper in the June, 2009 issue of Psychological Science by Michael Sayette, Erik Reichle, and Jonathan Schooler suggests one contributing factor. They looked at how alcohol affects mind wandering and also people's ability to detect that their mind is wandering.

Mind wandering happens when you are engaged in some task, and suddenly you find yourself thinking about something unrelated to the task. For example, you might be reading a riveting blog about drunk driving and then you may start thinking about romaine lettuce or an errand you have to run later in the day. Sometimes, when your mind is wandering, you realize that it is wandering. That is, you catch yourself drifting. In those cases, you can reorient yourself back to what you are trying to achieve. Other times, it may take you some time to realize that your mind has started to wander.

Sayette and colleagues had people read a section of the novel War and Peace. As they were reading, people were asked to press a button every time they noticed that their mind was wandering. This is a measure of how often people think their mind is wandering. In addition, every few minutes there was a signal (a beep), and people were asked if their mind was wandering at that time. This procedure allows the researchers to estimate how often people's minds were actually wandering.

Half of the people in this study participated after drinking enough alcohol to get their blood alcohol level above .05%. The other half drank a placebo that tasted a bit like alcohol, but did not actually have any alcohol in it.

So, what happened? Looking at the data from when people responded to a signal, the people who drank alcohol were mind wandering about twice as often as the people who did not drink alcohol. However, each group reported about the same number of episodes of mind wandering across the 30-minute experiment.

What does this mean?

If you just asked the people in this study how often their minds wandered during the study, the answers would be the same regardless of whether they drank alcohol. However, in actuality, mind wandering was twice as likely for those who drank alcohol than for those who didn't. So, the people who drank alcohol were not recognizing most of the times when their minds wandered.

What has this got to do with drunk driving?

When you have had a bit to drink and you think about driving home, you have to make a decision about whether it is safe for you to drive home. One thing you might do is to think about whether you are experiencing any obvious signs of impairment. For example, you might ask yourself whether you are having any trouble concentrating. But this study suggests that you are likely to think that you are concentrating just about as well when you have had a fair amount to drink as when you haven't had anything to drink at all, even though you are actually much worse at maintaining your concentration. So, your own beliefs about your ability to think while drunk are flawed.

That means that you should not rely on your own judgment about the effects of alcohol on your ability to think. Instead, if you plan to go out and have a few drinks, then set up a specific rule. If you have three or more drinks, don't drive home. Get a ride or take a cab. Avoid the risk that you'll end up in the newspaper.

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