The Voices Within: The History and Science of How We Talk to Ourselves
The Voices Within is an outstanding book--for the right sort of reader. That reader is someone who's interested in science, who's not put off by a modest dusting of scientific terminology, who's interested in the nitty-gritty details of experiments.
That's me, needless to say. If it's you, read The Voices Within. Your reward will be a wealth of fascinating and thought-provoking detail. Some of these are simple eye-openers: I would never have guessed, for example, that a non-trivial fraction of people report that they never think in words. Some of them are more food for thought: Fernyhough devotes quite a lot of space to exploring the connection between ordinary train-of-thought inner speech and the experience of people who hear voices. If the conclusions he draws are sometimes tentative, well, that's science for you.
In fact, Charles Fernyhough is a novelist as well as a scientist. The Voices Within doesn't always feature novelistic prose, although it does so in spots. There is, however, a short but interesting segment on how writers "hear" their characters' voices. The humanist connection comes through most clearly is in the deeply sensitive treatment of voice-hearers (Fernyhough avoids terms such as "auditory hallucinations"). The case histories that he cites are touching and memorable, as well as being illuminating.
This is a science that's still in its infancy. Only recently have scientists had the tools (fMRI, mainly) to investigate inner speech in any but the most rudimentary fashion. Even the questions themselves are still being refined. I hope that future books will be as enlightening as this one.