In the case of visible objects, size has about the same effect as intensity. The large features of the landscape are noticed before the little details. The advertiser uses large type, and pays for big space in the newspaper, in the effort to attract the attention of the reader.
[Footnote: Often he pays more than the space is worth; at least doubling the size of his "ad" will not, on the whole, double the amount of attention he gets, or the number of readers whose attention he will catch. The "attention value" of an advertisement has been found by Strong to increase, not as fast as the increase in space, but about as the square root of the space occupied.]
Another similar factor is repetition. Cover a billboard with several copies of the same picture, and it attracts more attention than a single one of the pictures would. Repeat a "motive" in the decoration of a building, and it is more likely to be noticed. Repeat a cry or call several times, and after a while it may be noticed, though not at first. The "summation of stimuli" has much the same effect as increasing the intensity of a single stimulus.
If, however, a stimulus is repeated or continued for a long time, it will probably cease to hold attention, because of its [{247}] monotony, or, in other words, because it lacks the element of change.
Striking quality is an advantage, quite apart from the matter of intensity. Saturated colors, though no stronger in intensity of light than pale colors, are stronger stimuli for attention. High notes are more striking than low. Itch, tickle and pain get attention in preference to smooth touch. "Striking" cannot be defined in physical terms, but simply refers to the fact that some kinds of stimulus get attention better than others.
Definite form has the advantage over what is vague. A small, sharply defined object, that stands out from its background, attracts the eye more than a broad, indefinite expanse of light such as the sky. In the realm of sound, "form" is represented by rhythm or tune, and by other definite sequences of sound, such as occur in the jingles that catch the little child's ear.
The factors of advantage so far mentioned are native, and a stimulus possessing one or more of them is a natural attention-stimulus. But the individual also learns what is worth noticing, and what is not, and thus forms habits of attention, as well as habits of inattention. The automobile driver forms the habit of attending to the sound of his motor, the botanist forms the habit of noticing such inconspicuous objects as the lichens on the tree trunks. On the other hand, any one forms the habit of not noticing repeated stimuli that have no importance for him. Move into a house next the railroad, and at first you notice every train that passes; even at night you awake with a start, dreaming that some monster is pursuing you; but after a few days the trains disturb you very little, night or day. The general rule covering attention habits is this: anything that you have to work with, or like to play with, acquires the power to attract your attention, while anything that you do nothing [{248}] with loses whatever hold on your attention it may have possessed by virtue of its intensity, quality, etc.
Besides these permanent habits of attention, there are temporary adjustments determined by the momentary interest or desire. Stimuli relevant to the momentary interest have an unwonted hold upon attention, while things out of line with this interest may escape attention altogether, even though the same things would ordinarily be noticed. What you shall notice in the store window is governed by what you are looking for as much as by the prominence of the object in the total display. When you are angry with a person, you notice bad points about him that you usually overlook, and any aroused desire adjusts or "sets" attention in a similar way. The desire or interest of the moment facilitates attention to certain stimuli and inhibits attention to others, and is thus an important factor of advantage.
The interest of the moment is often represented by a question. Ask yourself what spots of red there are in the field of view, and immediately various red spots jump out and strike the eye; ask yourself what pressure sensations you are getting from the skin, and immediately several obtrude themselves. A question sets attention towards whatever may furnish an answer.
To sum up, we may say that three general factors of advantage determine the power of any stimulus to attract attention. There is the native factor, consisting of change, intensity, striking quality, and definite form; there is the factor of habit, dependent on past experience; and there is the factor of present interest and desire.