The Elements of Scientific Psychology

Perception has been described in the loose terminology of the Anglo-German psychology, as "sensation plus imagination," with the further qualification that the pure sensation never (or seldom) occurs. In this formula, "sensation" means not the sentiendum, but the awareness of the sentiendum: which we have called, so far, sense perception: and perception means the being aware of complex objects, as including more than the sentienda which can actually be "sensed" at the moment of perception. Interpreted in such a way as to give the greatest intelligibility, the formula means that (1) perception, as it normally occurs, is more than sensation: and, (2) that the additional factor is imagination, or imagining. The first proposition is true; the second is false; and the best way to avoid confusion is to ignore the formula and consider the process of perception, as we have so far, as a reaction process.

We have been considering perception, up to this point, in its analytically simplest form, as the awareness of sentienda actually "presented" to the senses, ignoring the fact that we are usually aware, in such cases, of more than these immediately presented sentienda. We perceive color, for example, when certain visual stimuli act upon the retinal receptors; but in such cases we rarely perceive color alone: we perceive a colored object, and the object includes factors other than color, although these factors, in such a process of perception, are not presented to sense; that is, they correspond to no stimuli actually affecting receptors. It is now necessary to examine into the way in which such perceptual processes may arise. In this examination we must keep empirical facts constantly in view, and refer all our formulations to these facts. It is an easy matter in psychology, perhaps easier than in other sciences, to devise a set of terms, and then proceed to shuffle

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