Modern life may demand it and job descriptions often list it as a requirement, but multi-tasking is way beyond the capacity of the human brain, and even too much for the next best laptop computer. They just do so many single things so fast, they appear to be doing several things simultaneously.

In the human computer, multi-tasking — thinking about or doing two or more things at the same time — is more your ego talking than your brain working, even when bunching up routine activities, according to a slew of new research on human cognition.

Take talking on a cell phone while driving, for example. Three University of Utah psychologists did, and have found that passengers in a car being driven by someone talking on a cell phone are not only less distracting to good driving, they are more aware of traffic hazards ahead than the guy holding the steering wheel.

So, add another thing to the list that friends don't let friends do: Friends don't talk on cell phones or text friends who are driving.

"In both cases, you have a conversation, but when you take a look at the data, it turns out that a driver conversing with a passenger is not as impaired as a driver talking on a cell phone," said the U.'s David Stayer. "The passenger adds a second set of eyes and helps the driver navigate and reminds them where to go."

Stayer, who was joined in the study by Frank Drews and Monisha Pasupathi, also noted that a passenger in the car knows what the traffic conditions are like, as opposed to someone on the phone who is completely unaware.

The research is being released today, and their article, "Passenger and Cell Phone Conversations in Simulated Driving," will appear in the Dec. 15 issue of the Journal of Experimental Psychology: Applied.

The new research supports earlier findings by Strayer and Drews that hands-free cell phones are as distracting as handheld models: It's not the dialing, it's the conversation. In the latest findings, it's not the conversation, it's having one on the phone.

The agility of a younger mind is not a mitigating factor: The researchers have shown previously that young adult drivers on cell phones react no faster than an elderly driver and are as impaired as someone with enough alcohol in their system to be legally drunk.

And thinking both are conversations, ergo they're both the same thing, is ego again.

Yes, both are conversations, Stayer said, but the data show more or bigger lane deviations for someone talking on a cell phone compared with a driver talking to a passenger. When there is a passenger in the car, almost everyone takes the exit, he said. When it's a cell conversation, half will miss it.

The differences are apparent at the operational, tactical and strategic levels of performance, the researchers state. The study, which was done in a sophisticated driving simulator, not on the street, analyzed the driving performance of 41 mostly young adult drivers paired with 41 friends who served as conversation partners. Both sexes were equally represented.