The central problem of this book can be introduced by thinking about even the simplest cases of phenomenal consciousness. Let us, therefore, begin with afterimages, and let us fix our ideas by reference to a novelty item that some readers may have encountered. This item is similar to an American flag, only it is printed in green, black, and yellow. A caption instructs users to stare at the oddly printed flag for 10 seconds, in good light, and then to look at a white wall or a white piece of paper. The predicted, and actual, result is that one will then see an American flag in its correct colors.

The principle behind this novelty item is that afterimages brought about by brightly colored things will have the complementary colors of the objects that cause them. This principle can easily be verified by staring at some brightly colored thing in strong light, then looking at a white surface. Red or green will each produce the other, as will blue or yellow. This little experiment will also demonstrate that the distance of the afterimage will be the same as the distance of the surface upon which one's eyes are focused.

I want to know how red comes into the situation we are in when we have stopped looking at the printed “flag” and are having an afterimage in which we see red.