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The Perception Of Space

Many have been the philosophical controversies over the nature of space

and our perception of it. The psychologists have even quarreled

concerning whether we possess an innate sense of space, or whether it

is a product of experience and training. Fortunately, for our present

purpose we shall not need to concern ourselves with either of these

controversies. For our discussion we may accept space for what common

sense un
erstands it to be. As to our sense of space, whatever of this

we may possess at birth, it certainly has to be developed by use and

experience to become of practical value. In the perception of space we

must come to perceive distance, direction, size, and form. As a

matter of fact, however, size is but so much distance, and form is but

so much distance in this, that, or the other direction.

THE PERCEIVING OF DISTANCE.--Unquestionably the eye comes to be our

chief dependence in determining distance. Yet the muscle and joint

senses give us our earliest knowledge of distance. The babe reaches for

the moon simply because the eye does not tell it that the moon is out of

reach. Only as the child reaches for its playthings, creeps or walks

after them, and in a thousand ways uses its muscles and joints in

measuring distance, does the perception of distance become dependable.

At the same time the eye is slowly developing its power of judging

distance. But not for several years does visual perception of distance

become in any degree accurate. The eye's perception of distance depends

in part on the sensations arising from the muscles controlling the eye,

probably in part from the adjustment of the lens, and in part from the

retinal image. If one tries to look at the tip of his nose he easily

feels the muscle strain caused by the required angle of adjustment. We

come unconsciously to associate distance with the muscle sensations

arising from the different angles of vision. The part played by the

retinal image in judging distance is easily understood in looking at two

trees, one thirty feet and the other three hundred feet distant. We note

that the nearer tree shows the detail of the bark and leaves, while

the more distant one lacks this detail. The nearer tree also reflects

more light and color than the one farther away. These minute

differences, registered as they are on the retinal image, come to stand

for so much of distance.

The ear also learns to perceive distance through differences in the

quality and the intensity of sound. Auditory perception of distance is,

however, never very accurate.

THE PERCEIVING OF DIRECTION.--The motor senses probably give us our

first perception of direction, as they do of distance. The child has to

reach this way or that way for his rattle; turn the eyes or head so far

in order to see an interesting object; twist the body, crawl or walk to

one side or the other to secure his bottle. In these experiences he is

gaining his first knowledge of direction.

Along with these muscle-joint experiences, the eye is also being

trained. The position of the image on the retina comes to stand for

direction, and the eye finally develops so remarkable a power of

perceiving direction that a picture hung a half inch out of plumb is a

source of annoyance. The ear develops some skill in the perception of

direction, but is less dependable than the eye.