Three years ago, the New England Journal of Medicine published a highly influential study that said talking on a cellular phone while driving made you four times likelier to get into a car collision. As an accompanying editorial pointed out, however, the study didn't consider how much you could improve your odds by talking on a hands-free phone. To what extent did the danger arise from tying up the driver's hand, as opposed to tying up the driver's brain? If the latter posed a real risk, were drivers taking their lives into their hands by listening to Ian McKellen recite Robert Fagles' translation of The Odyssey, or by listening to Daniel Schorr discuss the upcoming China trade vote on National Public Radio, or for that matter, by listening to the conversation of any passenger?
Now the Journal of Experimental Psychology: Applied has weighed in with a partial answer. Its March issue carries a study by M.A. Recarte and L.M. Nunes, two psychologists in Madrid, of the extent to which thinking about something other than driving puts you in danger of having an accident. Recarte and Nunes monitored the eye movements of 12 drivers while they engaged in verbal and nonverbal mental tasks requiring about 30 seconds of concentration. The verbal task was to recite words beginning with a particular letter of the alphabet. The nonverbal task was to visualize successive letters of the alphabet and recite which letters looked the same when you flipped them over or turned them upside-down, or which letters were "open" (example: "E") and which were "closed" (example: "P"). According to Recarte and Nunes, the verbal and nonverbal tasks were equally demanding, as measured by the amount of pupil dilation they caused within an individual driver.
Under normal conditions, drivers dedicate about 1.4 percent of their "eye fixations" (i.e., glances) to looking at their rearview mirror. When performing a verbal mental task, that declined for the drivers under study to 0.4 percent. When performing a nonverbal mental task, it declined to 0.2 percent. Also, drivers normally dedicate about 4 percent of their eye fixations to looking at the speedometer. When performing a verbal mental task, that declined to 1 percent. When performing a nonverbal mental task, it declined to less than 1 percent. In addition, the nonverbal thought caused much "eye-freezing" (i.e., staring into space) and a narrowing of the "visual inspection window" (i.e., staring straight ahead). This was far less true when the drivers engaged in verbal thought.
All this suggests that if you take the trouble to get a hands-free cell phone for your car, you should stilltrynotto form a mental image of anything being said to you during the conversation. That means not trying to describe to your wife or husband exactly where on your desk you may have left your PalmPilot. It also means not trying to picture your wife or husband in the nude. On the other hand, feel free to dictate boring messages for your wife or husband to pass on to the dry cleaner or to utter obscenities like "Goddamn it!" that don't summon up specific mental images, or to have your wife or husband say "Goddamn it!" to you. If you're listening to Ian McKellen recite The Odyssey, pay more attention to the sound of the word "Cyclops" than to what a monster would actually look like if he had one eye in the middle of his forehead. If you're listening to Daniel Schorr on NPR, try not to wonder how much spittle he's getting on the microphone. If your college roommate is chatting with you from the passenger seat, try not to remember the floor plan of your junior-year dormitory. And so on.