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.