What you hold in your hands is a book, and consequently you are now immersed in its sensory environment. Your eyes follow the argument line by line and page by page; you can skip between chapters at your leisure; and once in a while you may find yourself thinking new thoughts. Reading and writing are efficient techniques of communication, and they have been fostered around the book (and scroll and clay tablet) for thousands of years. The experience of sound media is entirely different from the experience of the book. You tap your foot half-consciously to the funky beat of the music, and you imaginatively share the adventures of the foreign correspondent on radio while doing the housekeeping.