Multitasking is attempting to handle more than one task simultaneously. The human mind is not directly capable of this, thus it emulates multitasking by rapidly alternating between the tasks. This makes for a higher rate of errors due to lack of attention, and since context switching from one task to another is expensive, the sum of time spent on the tasks is larger than if the tasks were done sequentially. (Think green threads with a huge context switch cost with lots of deadlocks and race conditions.)1

Furthermore, our brain exercises something Dr. Meyer of the University of Michigan calls “adaptive executive control” where our brain assigns priorities to the tasks we are performing in parallel.2 For instance, when driving and talking in cell phone, our brain assigns a higher priority to responding to our phone conversation than focusing on the road. This deteriorates reaction time to worse than drivers intoxicated over the 0.08% legal limit.3

Multitasking impairs cognitive control

Stanford professors thought before their study on multitasking that people who frequently multitask must be excellent in recognizing important elements in a series of tasks:

In one experiment, the groups were shown sets of two red rectangles alone or surrounded by two, four or six blue rectangles. Each configuration was flashed twice, and the participants had to determine whether the two red rectangles in the second frame were in a different position than in the first frame.

They were told to ignore the blue rectangles, and the low multitaskers had no problem doing that. But the high multitaskers were constantly distracted by the irrelevant blue images. Their performance was horrible.4

Desperately they attempted to find tasks in which the frequent multitaskers performed better, such as short term memory and context switching, but multitaskers failed to show any improvement in any task the Stanford psychologists presented. Multitaskers have trouble paying attention and are easily distracted. They have their mind in a myriad of different places at the same time, not effectively processing any information.

One last theory involved the possibility of multitaskers being faster at context switching, performing this all the time, but even here their performance was inferior:

The test subjects were shown images of letters and numbers at the same time and instructed what to focus on. When they were told to pay attention to numbers, they had to determine if the digits were even or odd. When told to concentrate on letters, they had to say whether they were vowels or consonants.

Again, the heavy multitaskers underperformed the light multitaskers.

“They couldn’t help thinking about the task they weren’t doing,” Ophir said. “The high multitaskers are always drawing from all the information in front of them. They can’t keep things separate in their minds.”

Multitaskers worse at multitasking

Effectively, multitaskers train themselves to superficially consume multiple sources of input from memory and the external world. Their ability to filter relevance to their current goal declines and they are easily distracted by irrelevant information. Multitaskers actually become bad at multitasking, by multitasking.5

Multitasking students report to have more issues in their academic work. Students who browse Facebook and instant messaging while doing homework on average achieve lower grades in school.6 In 1999 16% of media consumption was combined, in 2005 26% of media was used together. This number must have skyrocketed since, with Generation Z and Y being its victims.7