A percept contains both less and more than the sensations corresponding directly to the stimulations. According to the conditions discussed under attention, certain sensations become focal at the expense of others which become marginal. For example, of all things impressing themselves upon my retina, only a few--usually, but not always, those in the center of the field of vision--attain a high degree of consciousness. And of these things again not all the qualities, but only a few become highly conscious. If, as in this case, the visible things happen to become highly conscious, the simultaneously existing audible or tastable things are apt to remain at a low degree of consciousness. That which is important for the needs of our daily life is specially favored and becomes a part of the percept. That which has no practical importance does not easily become a highly conscious part of the present mind. The variations in color of a gown forming many folds are rarely noticed. All parts of the gown are perceived as parts of the same substance. That the whole gown is made of one kind of cloth is practically important. That the various folds appear to the eye--because of the variation of the illumination--somewhat different, is of no practical consequence. Many quite common phenomena, after-images, overtones, difference tones, are never known by the majority of people, because of their practical unimportance. But a percept contains not only less, but also much more than the sensations corresponding to the stimuli of the moment. Numerous images are woven into this system of sensations and thus give additional meaning to it. We may be said to _see_ that the things are hot or cold, rough or smooth, heavy or light, although our eyes as mere sense organs cannot give us any such information. In the same way we may be said to see that the things are at this or that distance from our head, and that this thing is nearer, that thing farther from us, although our inherited ability to see things spatially does not give us any other information than that of shape and size in the field of vision. By incessantly repeated experiences we have learned, at an early age, that changes in the distance of things which in this or that way have come to our knowledge, are regularly accompanied by definite changes in their size, their coloring, their appearance when the right eye’s image is compared with the left eye’s image, and many similar changes of the impression. Whenever such signs of changes in the distance are impressed upon our mind, we immediately supplement them by ideas of the distances themselves. Thus our original two-dimensional perception of space is expanded into a three-dimensional perception.