To make it short: Humans are not good at multitasking.

Yet knowledge workers in Corporate America are being asked to do exactly that. They are expected to stay on top of incoming emails, sometimes hundreds a day. They are asked to be reachable, go to meetings, and handle multiple assignments with ease.  Multitasking is seen as a virtue. The ability to do so receives praise. However, multitasking comes at a significant cost.

In working with knowledge workers, I find many examples that show that our brains cannot fully focus when we multitask. People take longer to complete tasks and are predisposed to error. When we attempt to complete many tasks at one time or rapidly shift between them, errors go way up. Everything takes far longer than if the tasks were done sequentially. This is largely because the brain is forced to restart and refocus. A study found that for a time between each exchange, the brain makes no progress whatsoever. Therefore multitasking people not only perform each task less well, but lose productivity in the process.

Even computers are not always good at multitasking, as we find when we open too many applications and windows on our desktop machines. Our computers use hard drives as extended memories. If a computer cannot hold enough data in its memory, it pushes the data out to disk. If you have enough applications running in parallel, the system performance is reduced, because files have to be swapped back and forth between computer memory and hard disk. In computer science speak, this effect is called “thrashing.” You can bring any computer system to its knees by increasing the number of parallel processes; at that point we often need to re-boot.

A similar thing happens with the  human brain. Let’s say we write a document (task 1) and get interrupted by a phone call (task 2). 

1. Writing a document requires focus. Blood rushes to the anterior prefrontal cortex – the switchboard of our brain. It basically activates the brain region required to perform the task at hand.
2. Next there is the identification of the neurons within this region capable of completing the task, as well as the triggering of the actual task processing itself. This process is called “rule activation” and takes several tenths of a second to accomplish. We begin to write.
3. While we are typing, our sensory system picks up the ring tone of our cell phone. Speaking and engaging in conversation are handled by a different brain region. The process of disengaging from our writing task is managed through the anterior prefrontal cortex. We store enough information to resume this task later. Then task 2 is started (see steps 1 and 2).
4. We start another rule activation for task 2. We have real, measurable switching costs.

These are the steps that occur between two tasks. Imagine to what extent we are taxed with switching costs in a work environment where we process daily hundreds of emails, tens of calls, and multiple project assignments. Anything that can be done to bring focus in the work day, anything that can be done to bring hours of uninterrupted work time, will enhance productivity.

I have found in my work with corporate clients that people who are regularly interrupted take up to fifty percent (50%) longer to finish a task, even when they are not trying to switch between tasks. The number of errors also goes up by about that much. There are very effective excersises to demonstrate this effect. Keep that in mind when you organize your day.