Most people can rather efficiently walk and chew gum at the same time, but when it comes to more complicated "multi-tasking" – like driving and talking on a cell phone – there is a price to pay.
And no one, it seems, is immune.
"There is a cost for switching from one task to another and that cost can be in response time or in accuracy," said
Mei-Ching Lien, an assistant professor of psychology at Oregon State University. "Even with a seemingly simple task, structural cognitive limitations can prevent you from efficiently switching to a new task."
Psychologists who study multi-tasking have argued for years about whether these "information bottlenecks" occur because people are inherently lazy, or because they have a fundamental inability to switch from one task to another. New studies by Lien and her colleagues at the NASA Ames Research Center in California suggest it is the latter.
Results of their study have been published in the Journal of Experimental Psychology.
In their study the researchers asked volunteers to respond to a variety of auditory and visual cues then measured the responses. When the volunteers prepared for one task, such as responding to the color red, their responses were swift and accurate. When the researchers added a second element – the recognition of shapes as well as color – the task switch considerably delayed the responses, even when the volunteers were prepared for it.
"People are surprised that there is such a delay," Lien said. "Practice can help a person reduce the 'cost' of switching tasks, but it apparently cannot eliminate that cost."
Lien said the study can be applied to the real world, especially to drivers who talk on cell phones. On the surface, she said, it appears that drivers are trying to accomplish just two tasks – driving and conversing. But each task is complicated and multi-faceted, greatly increasing the "cost" of switching. The result: inattention and slow reaction times.
"A lot of people think talking on the cell phone while driving is natural, but each time someone asks a question or changes the subject, it's like taking on a new task," Lien said. "It requires a certain amount of thought and preparation. It's actually quite different than listening to the radio, where you don't need to respond.
"And it's also different from talking to a passenger in the vehicle," she added. "In most cases, a passenger can observe when there is a dangerous traffic situation and keep quiet. But someone calling you on a cell phone won't have a clue."
There are individual differences in the costs of multi-tasking, Lien said. In her lab studies, a typical response to a single stimulus might take 300 milliseconds. Adding a second task increases the response to about 800 milliseconds. A millisecond is 1/1000th of a second, so the delay may not seem like much – until you extend the difference to a car driving 60 miles an hour and realize the response rate more than doubles, Lien said.
In her lab studies, she has yet to test any volunteers who are immune to delays in multi-tasking, though she says some students do much better than others.
"I have to say that the best ones are those who play a lot of video games," she pointed out. "Those are lab studies, however, and not driving tests."
She became interested in multi-tasking while working at the NASA Ames Research Center in Moffett, Calif., where she was part of a team analyzing cockpit design and pilot function. One of the projects focused on how much information can safely and efficiently be included on screens and monitors so the pilots' delay and loss of accuracy are minimized.
"We learned to modify some of the screens to mitigate their weaknesses," she said.
While Lien's studies suggest that simplifying tasks leads to greater efficiency, technology is complicating everything we do – including driving. Drivers often use cell phones, CD players, global positioning systems, radar detectors, complicated dashboards and other devices. At the same time, they must navigate increasing traffic, read a plethora of signs, and handle other distractions.
"We may be undermining our ability to drive safely," Lien said.
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