This December the National Transportation Safety Board of the U.S. recommended a nationwide ban on cell phone use while driving. According to NTSB member Robert Sumwalt, "This (distracted driving) is becoming the new DUI. It's becoming epidemic.” For some, the NTSB recommendation is a sign of the forces of light winning the day, and for others, proof of the impending apocalypse. Regardless of your emotional reaction to the issue, the subject cuts right to the heart of questions about the attention capacity of the human brain.
 The essence of the NTSB’s problem with cell phones is that they are too distracting. Studies show that talking while using a hands-free headset is just as likely to cause accidents as talking without a headset. Human brains appear to be optimized to focus on one thing at a time. While it is, of course, possible to attend to two or more things simultaneously, we do neither task at the level of quality that is possible if it we were to do it on its own. fMRI scans show that learning while multitasking engages different areas of the brain than learning while single-tasking. 

The human brain does not do as well under multitasking situations, and driving while talking on the cell phone involves a particularly difficult sort of multitasking: doing a visual task (like driving) and doing an auditory task (like talking on the phone) at the same time. This sort of multitasking requires the use of two separate brain regions simultaneously. And a 2001 study by Marcel Just at Carnegie Mellon showed that when volunteers did one task at a time, they used 37 voxels (small brain regions), but when they did both a visual and an auditory task simultaneously, they only used 42 voxels—far less than double. The brain has only so much processing capacity, and adding new tasks bogs all of them down. As Just commented, “You can't just keep piping new things through, and expect the brain to keep up. With practice, the brain can become more efficient at carrying out multiple tasks, but performance is never as good as when the tasks are carried out independently.” 

But is talking on a cell phone fundamentally worse or different from talking to another passenger? At least a conversational passenger is also scanning the road and could help alert drivers to oncoming dangers—something a cell phone conversant can never do. There are plenty of other distractions to driving: children, radios, eating, even shaving or doing makeup. Though traffic fatalities are at their lowest point since 1949 (thanks to improved safety features, more seat belt usage, and safer roads), the threat of distracted driving still worries many policymakers in the wake of incidents like the Chatsworth Train Disaster, in which the engineer was texting while driving. And as more and more gadgets become available as possible sources of distraction, the level of distractedness across the board may be rising.

In his famous definition of attention, William James noted that it “...implies withdrawal from some things in order to deal effectively with others, and is a condition which has a real opposite in the confused, dazed, scatterbrained state" (1). It appears that today human attention is at an all-time premium, yet few of us seem to have enough to go around. The brain evolved under conditions that were almost certainly far less stimulating, and we’ve created an artificial environment where the intensity, duration, and variety of stimulation is beginning to tax the upper limits of normal attention. This may have some very interesting consequences in the near future, from bans on the use of some technologies (a la the NTSB stance or the cell phone ban in many schools), to the use of attention-boosting drugs such as Modafinil, to the proliferation of attention training techniques like mindfulness practice. Or we may just learn to turn the gadgets off when needed, just as we have learned as a culture that it’s not a good idea to drink and drive.

 1. James, William. Principles of Psychology. 1890. p.403