The costs of context switching

Multiple ScreensMulti-tasking doesn’t work but our lives demand it anyway. This leaves us with the problem of how to compensate for the productivity and quality losses generated by work environments that demand parallel processing our brains can’t handle.

Why can’t our brains multi-task and what happens when we try? Left brain/right brain discussions aside, we only have one brain and that brain is single-threaded; it’s built to work on one cognitive problem at a time. Most of us can manage to walk and chew gum at the same time, but we can’t read the paper and discuss changes in the day’s schedule with our spouse simultaneously.

The bottleneck is attention. When we pretend to multi-task, what we are doing is cycling focus among the tasks competing for our attention. Each time we switch focus, we have to re-establish where we were in our work when we left off before we can begin moving forward. We also have to set aside the work we were doing along with whatever supporting materials we were using.

This process of redirecting focus is a context switch. Context switching is expensive because complex tasks—writing a blog post, debugging code, analyzing sales data—depend on equally complex mental scaffolding. When writing a blog post, for example, that scaffolding can include notes on the points to be made, memory of relevant previous posts ideas about upcoming blog posts, links and open browser tabs to supporting research, and so on. That scaffolding might be spread across multiple computer screens and program windows. It might also handwritten notes or paper copies of relevant supporting articles. All of that supporting scaffolding, along with the current draft of the blog post, helps you build up the mental structures that eventually lead to a finished draft of your post.

Suppose now that I need to put aside the blog post in progress to take an incoming phone call from my boss. It’s a call about a proposal we are putting together for a client. It might be just a simple call to confirm a detail in the proposal document, or it might be a more complex discussion about whether to rethink and reorganize the entire proposal. Regardless, I need to set aside the work on the blog post and flush my mind of all the details. I then need to call to mind the salient details of the client and the draft proposal as the call unfolds. In the first moments of this call, I’m not likely to be terribly articulate or smart. As the call progresses, I may need to call up various supporting materials and gradually fill in an entirely new context to contribute to the conversation.

Switching tasks means that you have to also break down one context and stand up a new context before you can actually begin to do any meaningful work. When the call is complete, you need to reverse the process to resume work on your blog post. Will you recall the insight that was just coming into focus when you were interrupted by that call from your boss? Or is it lost forever?

How expensive is this context switch? Research from the world of software development (see Jeff Sutherland’s Scrum: The Art of Doing Twice the Work in Half the Time) suggests that switching between two projects can result in productivity losses of 20%. Add a third project to your list and the costs rise to 40%. This means that each project gets no more than 20% of your attention and focus. Is it any wonder then that professionals work the hours that they do?

Step one in solving any problem is recognizing it. Limiting the number of projects you are working on and carving out big blocks of time to focus exclusively on each project helps. This is the core advice of most time management gurus. Few of us, however, have that much control over our responsibilities. A more attractive target then is to think about ways to lower the costs of context switching. We’ll come back to that in the next post.

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