The other aspect of the Sense-Perceptive Process has to do with the mental interpretation of environment.

Both these aspects are distinctly practical.

You should know something of the weaknesses and deficiencies of the sense-perceptive organs, because all your efforts at influencing other men are directed at their organs of sense.

You should understand the relationship between your mind and your environment, since they are the two principal factors in your working life.

Chapter III

Figure 1 shows two lines of equal length, yet the vertical line will to most persons seem longer than the horizontal one.

Fig. 1.

In Figure 2 the lines A and B are of the same length, yet the lower seems much longer.

Fig. 2.

Those things look smallest over which the eye moves with least resistance.

In Figure 3, the distance from A to B looks longer than the distance from B to C because of the time we involuntarily take to notice each dot, yet the distances are equal.

Fig. 3.

For the same reason, the hatchet line (A–B) appears longer than the unbroken line (C–D) in Figure 4, and the lines E and F appear longer than the space (G) between them, although all are of equal length.

Fig. 4.

Filled spaces look larger than empty ones because the eye unconsciously stops to look over the different parts of the filled area, and we base our estimate upon the extent of the eye movements necessary to take in the whole field. Thus

the filled square in Figure 5 looks larger than the empty one, though they are of equal size.

Fig. 5.

White objects appear much larger than black ones. A white square looks larger than a black one. It is said that cattle buyers who are sometimes compelled to guess at the weight of animals have learned to discount their estimate on white animals and increase it on black

ones to make allowances for the optical illusion.

THIS MAN AND THIS BOY ARE OF EQUAL HEIGHT, BUT ASSOCIATION OF IDEAS MAKES THE MAN LOOK MUCH THE LARGER

The dressmaker and tailor are careful not to array stout persons in checks and plaids, but try to convey an impression of sylph-like slenderness through the use of vertical lines. On the other hand, you have doubtless noticed in recent years the checkerboard and plaid-covered boxes used by certain manufacturers of food products and others to make their packages look larger than they really are.

The advertiser who understands sensory illusions gives an impression of bigness to the picture of an article by the artful use of lines and contrasting figures. If his advertisement shows a picture of a building to which he wishes to

give the impression of bigness, he adds contrasting figures such as those of tiny men and women so that the unknown may be measured by the known. If he shows a picture of a cigar, he places the cigar vertically, because he knows that it will look longer that way than if placed horizontally.

A subtle method of conveying an idea of bigness is by placing numbers on odd-shaped cards or blocks, or on any blank white space. The object or space containing the figures always appears larger than the corresponding space without the figures.

This fact has been made the basis of a psychological experiment to determine the extent to which a subject's judgment is influenced by suggestion. To perform

this experiment cut bits of pasteboard into pairs of squares, circles, stars and octagons and write numbers of two figures each, say 25, 50, 34, 87, etc., upon the different pieces. Tell the subject to be tested to pick out the forms that are largest. The susceptible person who is not trained to discriminate closely will pick out of each pair the card that has the largest number upon it.

This test can be made one of a series used in examining applicants for commercial positions. It can also be used to discover the weakness of certain employees, such as buyers, secretaries and others who are entrusted with secrets and commissions requiring discretion, and who must be proof against the

deceptions practiced by salesmen, promoters and others with seductive propositions.

This examination can be carried still further to test the subject's credulity or power of discrimination. What is known as the "force card" test was originally devised by a magician, but has been adopted in experimental psychology. Take a pack of cards and shuffle them loosely in the two hands, making some one card, say the ace of spades, especially prominent. The subject is told to "take a card." The suggestive influence of the proffered card will cause nine persons out of ten to pick out that particular card.

Turning from illusions of suggestion, shape and size, another field of peculiar sensory

illusions is found in color aberration. Some colors look closer than others. For instance, paint an object red and it seems nearer than it would if painted green.

Aside from the obvious uses to which these sense-illusions can be put, they form the basis for a number of psychological experiments to test the abilities