There are two theories of ' importance. Helmholtz explained contrast as a r deception of judgment. If, for instance, a gray strip on a green background appears reddish, it is because it is seen as if through a green haze and the mind unconsciously infers that if the strip is gray it must appear reddish in order to compensate for the green. Except for an occasional text-book of physiology this theory.. has long since been given up; experiments may be devised which preclude the possibility of inference, and, furthermore, ,no explanation in.
terms of the unconscious is satisfactory to science. Wundt, in his early books, brought contrast phenomena under his theory of rela tivity. (See WEBER'S Law). He supposes that the effect results from the fact that we apper ceive all sensory and affective experiences in relation to each other. As against this theory James has pointed out that the contrast-effect is directly experienced, and it cannot by any logic be made to depend upon an act of apperception. Wundt, however, now recognizes the physio logical condition of contrast as a secondary principle of explanation.
The occurrence of contrast phenomena in feeling is doubtful. The opposition of affective qualities is not, as some authors assume, like that of color qualities. Pleasantness and un
pleasantness are opposites in the sense that they are mutually exclusive. A decrease of the one, therefore, does not mean an increase of the other, i.e., the change is in the direction of indifference, of no feeling at all. It is true that pleasantness and unpleasantness are logically opposed, but there is no experimental evidence of an enhancement of the one by the previous experience of the other.
In space perception the size of objects and length of lines often seem larger or smaller, longer or shorter by virtue of the presence of objects or lines whose size or length is logically opposed. The illusion is not due to a contrast effect as is often alleged, but to some brain habit or disposition which conditions the per ception.
Bibliography.—Hoffding, H., (Outlines of Psychology) (London 1891); James, William, (Principles of Psycholog.y) (New York 1890); Ladd, G. T., and Woodworth, R. S., (Physio logical Psychology) (New York 1911); Titch ener, E. B., 'Experimental Psychology) (New York 1901) Wundt, W., (Lectures on Human and Animal' Psychology) (New York 1901); Physiologische Psychologie1 (Leipzig...1910).