Chapter XIII

to prove that attention involves inward reproduction prove that discrimination involves it as well. In looking for any object in a room, for a book in a library, for example, we detect it the more readily if, in addition to merely knowing its name, etc., we carry in our mind a distinct image of its appearance. The assafœdita in 'Worcestershire sauce' is not obvious to anyone who has not tasted assafœtida _per se_. In a 'cold' color an artist would never be able to analyze out the pervasive presence of _blue_, unless he had previously made acquaintance with the color blue by itself. All the colors we actually experience are mixtures. Even the purest primaries always come to us with some white. Absolutely pure red or green or violet is never experienced, and so can never be discerned in the so-called primaries with which we have to deal: the latter consequently pass for pure.--The reader will remember how an overtone can only be attended to in the midst of its consorts in the voice of a musical instrument, by sounding it previously alone. The imagination, being then full of it, hears the like of it in the compound tone.

=Non-isolable elements may be discriminated, provided= =their concomitants change.= Very few elements of reality are experienced by us in absolute isolation. The most that usually happens to a constituent _a_ of a compound phenomenon _abcd_ is that its _strength_ relatively to _bcd_ varies from a maximum to a minimum; or that it appears linked with _other_ qualities, in other compounds, as _aefg_ or _ahik_. Either of these vicissitudes in the mode of our experiencing _a_ may, under favorable circumstances, lead us to feel the difference between it and its concomitants, and to single it out--not absolutely, it is true, but approximately--and so to analyze the compound of which it is a part. The act of singling out is then called _abstraction_, and the element disengaged is an _abstract_.

Fluctuation in a quality's intensity is a less efficient aid to our abstracting of it than variety in the combinations in which it appears. _What is associated now with one thing and now with another tends to become dissociated from either, and to grow into an object of abstract contemplation by the mind._ One might call this the _law of dissociation by varying concomitants_. The practical result of this law is that a mind which has once dissociated and abstracted a character by its means can analyze it out of a total whenever it meets with it again.

Dr. Martineau gives a good example of the law: "When a red ivory ball, seen for the first time, has been withdrawn, it will leave a mental representation of itself, in which all that it simultaneously gave us will indistinguishably coexist. Let a white ball succeed to it; now, and not before, will an attribute detach itself, and the _color_, by force of contrast, be shaken out into the foreground. Let the white ball be replaced by an egg, and this new difference will bring the _form_ into notice from its previous slumber, and thus that which began by being simply an object cut out from the surrounding scene becomes for us first a _red_ object, then a _red round_ object, and so on."

_Why_ the repetition of the character in combination with different wholes will cause it thus to break up its adhesion with any one of them, and roll out, as it were, alone upon the table of consciousness, is a little of a mystery, but one which need not be considered here.

=Practice improves Discrimination.=--Any personal or practical interest in the results to be obtained by distinguishing, makes one's wits amazingly sharp to detect differences. And long training and practice in distinguishing has the same effect as personal interest. Both of these agencies give to small amounts of objective difference the same effectiveness upon the mind that, under other circumstances, only large ones would have.

That 'practice makes perfect' is notorious in the field of motor accomplishments. But motor accomplishments depend in part on sensory discrimination. Billiard-playing, rifle-shooting, tight-rope-dancing demand the most delicate appreciation of minute disparities of sensation, as well as the power to make accurately graduated muscular response thereto. In the purely sensorial field we have the well-known virtuosity displayed by the professional buyers and testers of various kinds of goods. One man will distinguish by taste between the upper and the lower half of a bottle of old Madeira. Another will recognize, by feeling the flour in a barrel, whether the wheat was grown in Iowa or Tennessee. The blind deaf-mute, Laura Bridgman, so improved her touch as to recognize, after a year's interval, the hand of a person who once had shaken hers; and her sister in misfortune, Julia Brace, is said to have been employed in the Hartford Asylum to sort the linen of its multitudinous inmates, after it came from the wash, by her wonderfully educated sense of smell.

The fact is so familiar that few, if any, psychologists have even recognized it as needing explanation. They have seemed to think that practice must, in the nature of things, improve the delicacy of discernment, and have let the matter rest. At most they have said, "Attention accounts for it; we attend more to habitual things, and what we attend to we perceive more minutely." This answer, though true, is too general; but we can say nothing more about the matter here.

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