If you think you're being efficient when you perform three tasks at once, think again. According to a report published in the August issue of the Journal of Experimental Psychology: Human Perception and Performance, multitasking may actually reduce productivity.

When people juggle several tasks simultaneously, they use so-called executive control processes, which prioritize different tasks and assign cognitive resources to them. To study executive control, Joshua Rubinstein of the Federal Aviation Administration and University of Michigan researchers David Meyer and Jeffrey Evans decided to investigate how task-switching influenced performance in people who were assigned several tasks of varying familiarity and complexity.

Four experiments conducted using groups made up of between 12 and 36 participants revealed that switching between tasksin this case, solving math problems and classifying geometric objectstakes time, thus lowering performance. The team also found that switching between complex tasks took significantly longer than switching between simple ones. In explanation, the researchers note that task switching seems to take place in two stages: goal shifting and rule activation. Rule activation alone can take several tenths of a second, which can add up when a person switches back and forth between tasks frequently.

The new findings may have implications that reach beyond employee productivity: if it takes a driver half a second to switch his or her attention from a cell phone conversation to the road, the time lost to task switching can mean the difference between life and death.