The Stanford research team compared groups of people based on their tendency to multitask and their belief that it helps their performance. They found that heavy multitaskers were actually worse at multitasking than people who like to do a single thing at a time. The frequent multitaskers performed worse because they had more trouble organizing their thoughts and filtering out irrelevant information. They were also found to be slower at switching from one task to another. The authors wrote, "Multitasking reduces your efficiency and performance because your brain can only focus on one thing at a time. When you try to do two things at once, your brain lacks the capacity to perform both tasks successfully."
University of London researchers found that study participants who multitasked during cognitive tasks experienced IQ score declines. The IQ score drops of 15 points for multitasking men lowered their scores to the average range of an eight-year-old child.
Researchers said that while more research is needed to determine if multitasking is physically damaging the brain, it is clear that multitasking has negative effects.