Attention is less a lens on the world than a mirror for the mind. “My experience is what I agree to attend to,” William James wrote in his foundational treatise on attention in the final years of the nineteenth century. In the epoch since, we have discovered just what an “intentional, unapologetic discriminator” attention is, just how much it shapes our entire experience of reality . But we are only just beginning to discover that, far from a passive observer of the outside world, our attention is an active creator of it as the brain makes constant conscious and unconscious predictions of what it expects to find when it looks, then finds just that; we are only beginning to understand how right Thoreau was when, in James’s epoch, he observed that “we hear and apprehend only what we already half know.” That is what cognitive philosopher Andy Clark explores in The Experience Machine: How Our Minds Predict and Shape Reality ( public library ) — an illuminating investigation of the human brain as a prediction…