EFFECTS OF ATTENTION.
Another experiment will further illustrate this method of study. An apparatus is so contrived that a colored disk can be made darker or brighter by the operator, and a measure of the change be recorded. (See illustration on opposite page, rear group.) The persons operated on do not know what change is made, or whether any will be made or not. They first look at the disk for ten seconds, taking good note of its color. Next, the operator changes the shade (or not) as he sees fit. Then for another ten seconds the subject judges the shade of color, but this time performs meanwhile a sum in addition as the operator calls to him simple numbers.
The experiment is to determine how the appearance of the color changes, by reason of dividing the attention between observing the disk and performing the addition. Do the colors of a rival’s bonnet really grow more glaring the harder they are looked at? To explain this is to touch on a social as well as an esthetic problem.
Diversion of attention changes the appearance of distances as well as of colors. A large frame covered with black cloth stands vertical. Two tiny white disks are held in place on the cloth by invisible threads manipulated behind the frame by the operator. When the disks are set a given distance apart they rest close upon the smooth black ground. The eye sees but two white spots in a free field, and may judge the distance between them without complication. This is done for ten seconds, as with the color disks. Then the spots are covered, and their distance apart slightly changed (or not) by the operator. Again they are shown, and now judged for ten seconds while adding figures. The mental process of addition changes the judgment of the distance.
You will say it is a familiar experience that the road seems longer or shorter as the mind is busy or not. But it is not a familiar thing to determine the law of such lengthening and shortening for definite distances, and under precise mental condition, as in the above experiment.