ABSTRACT
As long ago as the 1880s, Galton ( 1822-1911) found that people differed greatly in their mental imagery. Some, like himself, had strong visual imagery; others had none at all, and thought mainly in words. This is as true today as it was then, and there are also individuals who have available both, though often with a preference for one or the other modality. (It is not, however, always easy to decide what kind of images people use, or indeed whether they have any at all.) In this chapter we shall be considering the two kinds of symbol, visual and verbal, which are used in mathematics, both in mental imagery and for all the other purposes served by symbols.
