refer the sensation of taste to a variety of body or substance which we know presentatively at the same moment and in the closest local connexion with the taste-stimulus.

In the case of smell, too, we gain a rudimentary sort of percept by means of movements and resulting changes of intensity in the olfactory sensations. Thus, by movements of the head or whole body in different directions, aided by the action of sniffing, we learn in a measure to localise olfactory sensations. Such projections into space of our sensations of smell may be rendered definite by the addition of contact with the nose itself. Thus, by bringing this organ into close proximity to the petals of a rose, the child is able to connect immediately the olfactory sensation corresponding to its odour with a tactually-perceived object. The fact that the dog habitually investigates objects with its nose suggests that it acquires percepts which resemble our own in being compounded out of movements and touches, but differ from them by the addition to the tactual element of the important adjunct, the maximum intensification of olfactory sensation.

The fact that our sensations of taste and smell are highly relative or subjective, that is, conditioned by varying organic circumstances, makes perception through these avenues a far less trustworthy process than that by means of touch and sight. Olfactory and gustatory perceptions are alike specially apt to be illusory, as when owing to an unhealthy condition of the tongue, or the persistence of the effect of a previous sensation, we mistake the quality of that which we are eating. The easy way in which children can be imposed on in the matter of tastes, as when they are told that the disliked mutton they are eating is pork, shows how readily we misapprehend through these senses.1

§ 33. Perception and Observation. All perception involves a measure of that reactive process which we call attention. But we are often able to discriminate and recognise an object or an action by a momentary glance which suffices to take in a few prominent marks. Such incomplete fugitive perception is ample for rough everyday purposes. On the other hand, we

1 For a like reason we are all liable to illusions of taste and smell, that is, the projection into the external world of purely subjective sensations arising out of disturbances of the organ itself.

PERCEPTION AND OBSERVATION.

275

sometimes need to throw a special degree of energy into the psycho-physical process of perception so as to note completely and accurately what is present. This is particularly the case with new and unfamiliar objects. Such a careful direction of the mind to objects is known as Observation. This observation may be carried out by way of any one of the senses, as when a lady tactually examines the texture of a fabric. The term commonly refers, however, to a careful visual scrutiny of objects.

Observation in its highest form is a methodical process. It implies a deliberate selection of an object for special consideration, a preparatory adjustment of the attention, and an orderly going to work with a view to see what exactly takes place in the world about us. This methodical procedure is specially conspicuous in scientific observation, as that of the astronomer, or the chemist. Such observation commonly involves, further, a prolonged and patient attention to changes in an object, or to a process. Observation may thus be said to be regulated perception.

Good observation consists in careful and minute attention to what is before us. Thus, in order to observe nicely a particular flower or mineral, we must note all the individual characteristics, the less conspicuous as well as the more prominent. Similarly, if we wish to observe a process such as evaporation, or the movements of expression in a person's face, we must carefully seize all the stages of the operation. By such a close effort of attention we give distinctness to our observations and accurately mark off what we are observing from other and similar objects with which they are liable to be confused.1

It may be added that good observation includes a certain self-restraint, a resolute limitation of attention to what is actually presented, and an exclusion of all irrelevant imaginative activity. Thus it includes in the carefully-trained mind the inhibition of the impulse to go beyond the observed facts in what is called inference, a common fault of bad observers, as the witness-box in our law courts illustrates. Also it involves the restraining of the impulse to look out for a

1 We might call a percept distinct when we see an object apart from other and surrounding objects, and clear when we mentally grasp all its parts or details.

particular thing when this grows into prepossession. The undisciplined mind is apt to see what it expects, wishes, or it may be fears to see. Even scientific observation has been. vitiated by a strong prepossession or expectation of a particular appearance. In like manner the undisciplined mind tends, like the Professor in the Water Babies, to overlook that which it is disinclined to believe in. Methodical observation must, no doubt, as the history of physical science tells us, be stimulated and guided by anticipation or imaginative conjecture. We should, in many cases, not see things at all if we were not on the look-out for them. At the same time, good observation never allows itself to be overshadowed or interfered with by such imaginative activity.1

It is less easy to draw up definite rules for the regulation of the perceptual process in observation than for that of the reasoning process. Good observation comes from a trained habit, and is the resultant of a combination of forces such as a strong interest in objects, zealous regard for fact or reality, and so forth. Education can, under favourable natural conditions, do much to develop observation and perfect the child in the use of the senses; but it attains this object not so much by laying down any definite rules, as by exercising the child in observing, and so producing a habit of accuracy."

REFERENCES FOR READING.

For a fuller account of the way in which we learn to localise impressions and perceive objects the reader is referred to Prof. Bain's treatise, Senses and Intellect, under 'Sense of Touch,' § 13, etc.; under 'Sense of Sight,' § 12, etc.; and later, under 'Intellect,' § 33, etc.; also to the excellent analysis of perception in Mr. H. Spencer's Principles of Psychology, vol. ii. pt. vi. chaps. ix. to xviii. With these may be compared M. Taine's interesting chapter on 'External Perception and the Education of the Senses,' On Intelligence, pt. ii. bk. ii. chap. ii. Among more recent works in English are to be noticed Ward's article, "Psychology" (Encyclop. Britann.), p. 51 ff.; and W. James's Principles of Psychology, vol. ii. chaps. xix. and xx. For a knowledge of the current German theories of space-perception the reader should consult Lotze, Metaphysic, bk. iii. chap. iv.; Wundt, Physiolog. Psychologie, vol. ii. caps. xi.-xiii.; Stumpf, Ueber den psychologischen Ursprung der Raumvorstellung; and my articles on "The Question of the Visual Perception in Germany," Mind, vol. iii. The relation of the psychological to the philosophical aspect of perception is touched on below, Appendix C.

The bearing of the psychology of perception on the corresponding philosophical problem, viz., the nature of the external reality perceived, is discussed below, Appendix C.

1 On some of the effects of prepossession in vitiating observation, see the account of illusory perception in the author's volume, Illusions, chaps. iii., vi.

? On the logical control of observation, see J. S. Mill, bk. iv. chap. i.

CHAPTER IX.

REPRODUCTIVE IMAGINATION: MEMORY.

81. Regions of Presentation and Representation: Sequence of Percept and Image. The percept is the immediate outcome of the organisation of certain portions of our sense-experience. It is, moreover, as we have seen, though taking up into itself a representative element, coloured throughout by its sensuous base. Hence we mark it off from the higher region of ideation as a presentation or direct sense-presentment.

Presentations or percepts, though the foundation of all our thought respecting things, are in themselves fugitive psychical phenomena. A percept, depending as it does (in normal circumstances) on a peripheral stimulus, ceases when that stimulus is withdrawn. In order, then, to that permanent psychical product which we call cognition something more than perception is necessary. This additional factor is supplied by that consequent or after-effect of the percept which we popularly call an idea, but which is more accurately described as a mental image, or representative image.1 Thus the percept called forth by a colour-stimulus is followed (under favourable conditions) by an image of that colour.

Here, as pointed out when dealing with the processes of psychical elaboration, we have the fullest manifestation of that psycho-physical property which we call retentiveness. In the persistence of the image after the percept we find a purely representative phenomenon, which stands out clearly from

1 The term image in psychology points to a double distinction. On the one hand it is representative, whereas a percept is presentative (or largely so); on the other hand it is a representation of a concrete object, or a mental picture, and is thus distinguished from a concept or general notion which typifies a class of things. The terms 'idea' and “ideation" are commonly used to include both images and concepts, or imagination and thought, thus marking off the whole region of the internal and representative from the external and presentative.

presentative phenomena.

In normal circumstances we all mark off the image from the percept by referring the former to the internal, the latter to the external or sensuous region of our experience. The precise nature and extent of the difference between the percept and image will be dealt with presently.

THE IMAGE.

§ 2. Transition from Percept to Image: (a) The After-image. It was pointed out above that sensations have a temporary persistence under the form of the after-sensation. Since all sensations in mature consciousness instantly develop into percepts, we may express this fact of temporary retention as follows: All percepts, whether visual, auditory, or other, tend under certain circumstances to persist beyond the moment of the cessation of the sensory stimulus. Thus the perception of a bright object, as the setting sun, is often followed for some seconds by that which is known as an after-image,' but which may be just as appropriately described as an 'after-percept,' of the object. Similar after-percepts sometimes occur in the case of hearing, touching, and so forth. All such after-images are due to the continuance of the process of excitation in the nervecentres engaged in the formation of the percept.

6

These after-images just referred to are known as 'positive'. They commonly occur immediately after the percept, and may be regarded as a prolongation of the same; but, in other cases, they recur for some little time, as, for example, after severe and protracted fixation of the eye on a microscopic preparation.1 They are distinguished from 'negative' after-images, which arise from a temporary fatigue and disablement of the retina, either of all its supposed constituent elements (answering to different colours) or of some of these. The first effect is illustrated by the transformation of a positive after-image of a bright object, say the window, into a black image. The second effect is illustrated by the familiar coloured images known as complementary spectra.

The (positive) after-images, or after-percepts, are phenomena of great psychological interest in relation to mental reproduction. They form the connecting link between percepts and images properly so-called (revived images). They approximate closely to complete percepts in respect of their psychical marks, namely, vividness or intensity (i.e., degree of luminosity and strength or 'saturation' of colour), distinctness of parts, and definiteness of localisation (either in the field of objects if the eyes are open, or in the dark field if they are shut). The chief difference consists in this, that they appear to shift their position in the field of view with every movement of the eyes. Thus the after-image of the sun's disc seems to

1 See Ward, loc. cit., who calls these recurrent sensations.