The biggest distraction in your car might not be the smartphone in your hand. It could be the biochemical circuitry between your ears.

The brain’s habit of drifting off into daydreams is still the biggest cause of distracted driving crashes, according to an insurance company’s recent analysis of federal traffic safety data.

Yet one of the best ways to keep the mind on task is to find it something else to do that offers some stimulation — but just not too much, said Paul Atchley, a professor of psychology at the University of South Florida in Tampa. Simple word games can help, and tuning into a radio program or a podcast is better than nothing — but both are much less distracting than a telephone conversation, even with a hands-free device, he said.

Atchley, who has used Ira Glass’s “This American Life” in research, said these forms of passive stimulation engage the mind but, unlike a conversation on a mobile phone, require very little of us.

“If you think about the social demands of a radio, it’s nonexistent. Ira Glass is not going to leap out of the radio and say, ‘Are you listening to my podcast?’ ” Atchley said.

The analysis of daydreaming’s role in fatal crashes comes as researchers focus increasing attention on the impact of smartphones on distracted driving and traffic safety.

Quintin Elliott, Virginia’s deputy transportation secretary, told a meeting of the Commonwealth Transportation Board last month that distracted driving is a “serious epidemic” that is also underreported, WTOP says. Other state officials say the phenomenon might have a bearing on the sharp increase in motorcycle fatalities, according to the Richmond Times-Dispatch.

Some researchers say the phone itself — all that entertainment and connectedness in a single tool in one’s fist — is to blame. Others wonder whether the ubiquitous cellphone and the Web have even shaped the way we think, making a whole generation intolerant of boredom and ever in search of distraction.

But whether the phone is truly the culprit is still not clear to traffic safety researchers studying the hard data.

Erie Insurance, citing its analysis of data compiled by the National Highway Traffic Safety Administration (NHTSA), says that 1 in every 10 fatal crashes involves some form of driver distraction, and of those, 61 percent involved a driver who was daydreaming. That compares to about only 14 percent who were using a mobile phone.

The insurance company — which said it consulted with the Insurance Institute for Highway Safety in its analysis — acknowledges that daydreaming is broadly defined and difficult to verify in a fatal crash. The company also notes that phone-related distracted driving is almost certainly underreported. Drivers who are involved in crashes are unlikely to admit that they were using mobile phones, for obvious reasons.

But in examining data between 2012 and 2016, the company found that in fatal crashes involving at least one distracted driver, the person was said to be “generally distracted” — which means inattentive or careless for an unknown reason — or “lost in thought,” i.e., daydreaming.

It’s the brain’s attempt to be creative, Atchley said. Instead of staying on task, the mind wanders on its own journey, sometimes finding new associations between ideas.

“There’s something about spacing out that’s healthy for us,” he said.

But the shift in attention also means a shift between active regions of the brain, and the brain has difficulty managing both.

“There are regions of the brain that we would call task-oriented. So when you’re focusing and concentrating, these regions are active. When you start to daydream or space out, other regions of the brain come online,” Atchley said. “The problem is that those task-oriented brain networks and those spacing-out networks aren’t really compatible. You can’t really have both active at the same time.”

Of course, that’s also when drivers who are tired, bored or prone to daydream might also be tempted to reach for the mobile phone. But research by Atchley and others shows that this is a mistake.

Talking with someone on a phone is much more distracting to a driver than even talking to someone in the car. When conversing inside the vehicle, a passenger will generally vary the conversation’s level of intensity and engagement in sync with traffic conditions the driver faces, Atchley said.

The person on the phone can’t see what the driver is seeing or what’s happening on the road, however, so the conversation tends to flow with the same degree of intensity and engagement no matter what’s happening, Atchley said. He said the driver’s social need to remain engaged with another human being also makes it harder to break off.

“It becomes the primary task,” Atchley said.

That’s where passive stimulation or listening to the radio can be more helpful than chatting.

In a study published by the Journal of Human Factors and Ergonomics Society, Atchley found a strategically timed verbal task helps keep a driver alert during a long trip. The experiment, using a driving simulator and instruments that measure brain activity, involved asking the subjects to free-associate on words spoken to them.

Some were asked to play the word game only toward the end of the 90-minute drive, while others played the word game every couple of minutes during the drive. Another group  listened to “This American Life,” and still another had no verbal task or stimulation at all.

The researchers found that drivers who played the word game toward the end of their 90-minute drive were the most engaged and alert. They were also less likely to drift out of the lane than drivers who played the word game continuously, listened to “This American Life” or did nothing. Drivers who listened to the radio program performed better than those who had no verbal task and nothing but the open, simulated, road to keep them company.

Atchley said the sweet spot is finding something that stimulates the mind, but less than the latest lowdown from your friend on a cellphone.

“We could never get people to ignore the conversation — the social demands are so strong.”

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