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Multitasking. Most of us have tried it since digital devices became unavoidable.

Now a study finds that some tasks are tougher to do at the same time than others.

Researchers had two groups of people complete a puzzle on a computer screen. One group also gave directions to another person via instant messaging. The other group gave the directions through an audio chat.

Subjects who performed the visual and audio task had a 30 percent drop in their puzzle performance. But those who performed two visual tasks—the puzzle and instant messaging—had a 50 percent drop in puzzle performance. The study is in the journal Computers in Human Behavior.

Using the same sensory system for two tasks actually uses up our attention capacity more quickly and completely than if the task requires two separate systems.

Both groups thought they did better than they actually did. But those who did two visual tasks thought they did even better than the other group did, though the opposite was true.

The researchers note that people may wrongly perceive visual tasks as effortless. Which might explain why some people continue to text while driving, sometimes with disastrous results.

—Christie Nicholson

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