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.
4. THE PERCEPTION OF TIME
The philosophers and psychologists agree little better about our sense of time
than they do about our sense of space. Of this much, however, we may be
certain, our perception of time is subject to development and training.
Nature of the Time Sense.—How we perceive time is not so well understood as
our perception of space. It is evident, however, that our idea of time is simpler
than our idea of space—it has less of content, less that we can describe. Probably
the most fundamental part of our idea of time is progression, or change, without
which it is difficult to think of time at all. The question then becomes, how do
we perceive change, or succession?
If one looks in upon his thought stream he finds that the movement of
consciousness is not uniformly continuous, but that his thought moves in pulses,
or short rushes, so to speak. When we are seeking for some fact or conclusion,
there is a moment of expectancy, or poising, and then the leap forward to the
desired point, or conclusion, from which an immediate start is taken for the next
objective point of our thinking. It is probable that our sense of the few seconds