A more detailed treatment of sensation is given in the author’s Text-book of Psychology, 1910, 46 ff., 201 ff. The reader may further consult: J. H. Parsons, An Introduction to the Study of Colour Vision, 1915; H. L. F. von Helmholtz, On the Sensations of Tone as a Physiological Basis for the Theory of Music, translated by A. J. Ellis, 1895; C. S. Myers, A Text-book of Experimental Psychology, pt. i., 1911, chs. 2-8, 18, 19; G. T. Ladd and R. S. Woodworth, Elements of Physiological Psychology, 1911, pt. ii., chs. 1-3; W. Wundt, Lectures on Human and Animal Psychology, 1896, Lects. 2-7; various articles in Dictionary of Philosophy and Psychology, ed. by J. M. Baldwin, vols. i., ii., 1901-2; the chapters on sensation in E. A. Schäfer, Text-book of Physiology, ii., 1900, and W. H. Howell, A Text-book of Physiology, 1908; E. Mach, Contributions to the Analysis of the Sensations, trs. by C. M. Williams, 1910; E. B. Titchener, Experimental Psychology, II., ii., 1905, Introduction.
The special references to smell will be found in E. B. Tylor, Anthropology, 1881, ch. ix., 207; W. W. Skeat and C. O. Blagden, Pagan Races of the Malay Peninsula, i., 1906, 200; F. Galton, Psychological Review, i., 1894, 61 ff.; and those to Dalton in W. C. Henry, Memoirs of the Life and Scientific Researches of John Dalton, 1854, 24, 49, 172, 187. For the term kinæsthesis see H. C. Bastian, The Brain as an Organ of Mind, 1885, 543.
[CHAPTER III]
Simple Image and Feeling
Conceptions and apparitions [sensations and images] are nothing really but motion in some internal substance of the head; which motion not stopping there, but proceeding to the heart, of necessity must there either help or hinder the motion which is called vital; when it helpeth, it is called pleasure; but when such motion weakeneth or hindereth the vital motion, then it is called pain.—Thomas Hobbes
§ 17. Simple Images.—Common sense draws a sharp distinction between our present perception of an object or event, and our later revival of it in memory; and psychologists have been accustomed, in the same way, to distinguish the simple sensation, the elementary process in perception, from the simple image, the elementary process in memory. In fact, however, it is very doubtful if there is any real psychological difference between sensation and image. The statement is often made that the image is weaker, fainter, more fleeting than the corresponding sensation. Thus, the great philosopher David Hume (1711-1776) wrote: “All the perceptions of the human mind resolve themselves into two distinct kinds, which I shall call impressions and ideas. [Hume’s terminology is different from ours.] The difference between these consists in the degrees of force and liveliness, with which they strike upon the mind.” Hume himself admits that “in sleep, in a fever, in madness, or in any very violent emotions of soul, our ideas may approach to our impressions; as on the other hand it sometimes happens that our impressions are so faint and low, that we cannot distinguish them from our ideas.” It is certain that sensation and image are often confused; and some writers have accordingly proposed to drop the term ‘image’ and to replace it by ‘secondary sensation.’ Let us look at the facts.
There is no department of sense in which sensation stops entirely when its stimulus is removed; in all cases, even in that of sound, the sensation is prolonged, for a longer or shorter time, and either after an interval or without interruption, in what is called the positive after-image. Blow out a match in the dark, and wave the glowing stem about; you see complete circles or figures of eight; the sensation persists, although the stimulus has passed from one part of the retina to another. In some departments, the positive is followed by a negative after-image; we have already mentioned the antagonistic after-images of sight. So the removal of a continued warm stimulus leaves a sensation of coolness; and the swimming in the head that you feel while twirling round is followed, when you come to rest, by a swimming in the opposite direction. Lastly, the name of memory after-image has been given to an experience which is most familiar, perhaps, in the taking of dictation; as you write the words last spoken, the speaker’s voice still rings in your ears; the sound hangs for a few seconds, as if arrested, and your pen is guided by the mental echo. Similarly, an attentive glance at an object may set up a sort of photographic image that remains distinct for several seconds.