Attention is much more than the cognitive function it is often taken to be – it is the very basis of our being in the world. A deep and meaningful experience of life depends to a large extent on our ability to maintain focus, which, in turn, depends on filtering out distracting stimuli. But the digital technologies on which we have come to rely for the smooth running of daily life are designed to distract us. A relentless stream of notifications, emails, posts and tweets exposes us to so much information that it becomes hard to assess what is actually relevant. When the brain’s filtering capacity is overloaded like this, a vicious circle is set up in which we become increasingly open to distraction. This not only makes us less efficient and less creative but also has profound implications for our mental health.

This assault on our attention span is the subject of Johann Hari’s latest book, Stolen Focus. He has written two books on addiction and depression, and this book is in some ways a development of the themes he explored in them. Hari cites recent research on teenagers which found that they could sustain focus on one