§ 3. Likeness of Object as Perceived and Object as Imaged.* — The image is a reproduction of the percept; these must therefore agree in their nature. But the reproduction is easily distinguishable from the original; there must therefore be an important difference or differences. The points of agreement are at least in part easy to assign. The sensible qualities such as colour, sound, etc., in all their varieties enter into the composition both of the percept and of the image, and these qualities can only appear in an image because they have previously appeared in a percept. The complication also and in general the spatial and temporal form of these qualities are common to both percept and image. Both the sensible qualities and their forms of combination originate primarily in the percept and are merely reproduced in the image. The reproduction varies greatly in degree of accuracy and completeness. Here individual differences are very conspicuous. Some can scarcely recall colours at all; others can do so with great vividness and accuracy. A person who almost entirely lacks the power to image colours may be capable of reproducing sounds with precision and distinctness. Some men seem quite incapable of reproducing odours; others can reproduce odours more vividly than any other sensible qualities.
* In what follows the object as perceived is simply called the "percept," and the object as imaged, the "image."
These differences have an important influence on the general character of ideational process in different individuals. There are some who work mainly with visual imagery, others with auditory and others with ideal revivals of motor experiences. Between these extreme types there are of course manifold intermediate gradations.