Page:The New International Encyclopædia 1st ed. v. 05.djvu/412

* CONTKAST. 352 CONTRAYERVA. along the line of junction of disk and ground. These experiments may be varied in many ways. Disks for mounting upon the color-mixer, to sliow bright- ness and color contrast. The blacli portions of the disks are black, the white portions white, and the shaded por- tions of some color. From Helmholtz, Physiol. Optik (isy6w) The principal laws of contrast, as determined by such experiments, are five in number: (a) Contrast always takes the direction of greatest opposition. A white induces a black, a color its complementaiy color. (See Visual Seistsa- TION.) (b) The more saturated the color (the redder the red, the purer the white), the greater is the contrast effect, (c) The contrast effect is greatest along the line of junction of the con- trasting surfaces (marginal contrast). (d) The more nearly alike two colors are in bright- ness ( both bright, or both dull ), the better will be the contrast effect. And (e) the more nearly homogeneous the contracting surfaces (the less distinction there is at the line of junction) ,_ the better will be the contrast effect. Helmholtz sought to explain tnese facts, in purely psycho- logical tenns, as deceptions of judgment; we see aright, but estimate wrongly; and Wundt ac- cepts the explanation for certain of the phe- nomena. The psj'chological theory, however, breaks do-v when one attempts to carry it out in detail. There can be no doulit whatsoever that, as Hering maintains, contrast of color and brightness is a matter of direct physiological con- ditioning, the result of the interaction of excita- tions within the visual organ, a symptom or expression of the functional unity of the retina. (2) Whether contrast occurs in the perceptual sphere ; whether, e.g. 'great' and 'small' contrast af. do blue and yellow, is a much-disputed ques- tion. There are certain optical illusions (see Illusions) which seem to be most easily 'ex- plained' by reference to a law of space contrast. In its most direct form, the theory of spatial contrast affirms that "the space sensation of a stimulated retinal point is a function pri- marily of the position of the point stimu- lated, but also of the space sensations of the neighboring retinal elements" (Loeb) ; the formula that holds of sensation is thus applied, without modification, to the sphere of visual space-perception. It has been said, again, that lines of different direction exercise 'contrastive' influences upon the movements of regard, i.e. upon the movements made by the eyes as we attentively follow the course of the lines (Hey- nians). And, lastly, it has been asserted that figures of the same size, surrounded by like figures of another size, look larger 'by contrast' if the surrounding figures are smaller, and smaller if these are larger (Wundt). Most of these illusions can, however, be otherwise ex- plained; and, despite the array of authorities, the fact seems to be that a given ])erce])tion is never really changed by contrast with other per- ceptions. 'Perceptual contrast' consists rather in a feeling. ^Vhen we see a middle-sized man by the side of a dwarf, we are surprised at his height; when we see him by the side of a giant, we are disappointed in his height. Our percep- tion of the man's height is not affected by the neighliorhood of smaller and larger men; the contrast that we 'feel' is felt, literally, as sur- prise or disappointment. (3) Many psycliologists, again, assume the existence of an affective contrast (see Affec- tion) ; a particular pleasure appears more IJJeasant if it follows a preceding unpleasantness, and vice versa (Fechner. Hiifl'ding, Lehmann). rile afl'ective value of a stimulus, however, is not constant, as is its sensation value, but varies with the present state of the organism and the corresponding disposition of consciousness. The 'particular' pleasure, then, is not a determinate amount of pleasantness, that may 'seem' to be greater or less according to its affective setting. Tiie pleasure actually aroused may differ within wide limits, while the stimulus remains the same. Moreover, where there is affection, there is also sensation; where there is affective con- trast there must also be a 'perceptual contrast,' in the sense just defined of the conditions of the arousal of a contrast-feeling. It is, then, per- haps safer to give up the idea of an 'affective contrast' altogether. (4) Lastly, we must note that, in certain psychological systems (Wundt, Hiiffding), the law of contrast figures as a general law of the mental life. Wundt, e.g. speaks of the 'law of psychical contrasts' as one of the three psycho- logical laws of relation; all "volitional pro- cesses . . . are arranged in groups made up of opposite qualities; . . . these opposites obey in their succession the general law of intensification through contrast. . . . The law is secondarily applied to ideas and their elements." The rejection of this law does not necessarily carry with it the rejection of spatial and affective contrast; though its acceptance 'ould naturally incline us to accept the alleged illustrations of its working. Consult : Fechner, Vorschule der Aesthetik (Leipzig. 1876) ; Lehmann, Hauptgesetze des menschlichen GefUhlslebens (Leipzig, 1892) ; Wundt, Ontlinea of Psychology (Leipzig, 1808) ; Hoffding, Oil f lives of Psychology (London, 1891); Titchener. Experimentiil Psychology (New York, 1901) ; Wirth. in Zeifschrift fur Psychologic, vol. x'iii. (Leipzig, 1898). CONTEAT SOCIAL, koN'tra' so'.se'aF. See Rousseau, .Jean .Jacqiies. CON'TRAYER'VA (Sp. contrayerba, anti- dote, from contra, against -{■ yerha, Lat. herha, Engl. herb). A medicine once in much repute against low fevers and as a mild stimulant anr", diaphoretic, but not used in the LTnited States. It consists of the rootstocks (rhizomes) of different