(7-column head) One hundred years ago this week there was launched at New York the ship Savannah, which may be called the father of the scores of steamers that are now carrying our soldiers and supplies from the New World to the Old World. ... Read more of CENTENNIAL OF THE FIRST STEAMSHIP TO CROSS THE ATLANTIC at Difficult.caInformational Site Network Informational
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The Nature Of Sensation








SENSATION GIVES US OUR WORLD OF QUALITIES.--In actual experience
sensations are never known apart from the objects to which they belong.
This is to say that when we see yellow or red it is always in
connection with some surface, or object; when we taste sour, this
quality belongs to some substance, and so on with all the senses. Yet by
sensation we mean only the simple qualities of objects known in
consciousness as the result of appropriate stimuli applied to
end-organs. We shall later see how by perception these qualities fuse
or combine to form objects, but in the present chapter we shall be
concerned with the qualities only. Sensations are, then, the simplest
and most elementary knowledge we may get from the physical world,--the
red, the blue, the bitter, the cold, the fragrant, and whatever other
qualities may belong to the external world. We shall not for the present
be concerned with the objects or sources from which the qualities may
come.

To quote James on the meaning of sensation: All we can say on this
point is that what we mean by sensations are first things in the way of
consciousness. They are the immediate results upon consciousness of
nerve currents as they enter the brain, and before they have awakened
any suggestions or associations with past experience. But it is obvious
that such immediate sensations can be realized only in the earliest
days of life.

THE ATTRIBUTES OF SENSATION.--Sensations differ from each other in at
least four respects; namely, quality, intensity, extensity, and
duration.

It is a difference in quality that makes us say, This paper is red,
and that, blue; this liquid is sweet, and that, sour. Differences in
quality are therefore fundamental differences in kind. Besides the
quality-differences that exist within the same general field, as of
taste or vision, it is evident that there is a still more fundamental
difference existing between the various fields. One can, for example,
compare red with blue or sweet with sour, and tell which quality he
prefers. But let him try to compare red with sweet, or blue with sour,
and the quality-difference is so profound that there seems to be no
basis for comparison.

Differences in intensity of sensation are familiar to every person who
prefers two lumps of sugar rather than one lump in his coffee; the sweet
is of the same quality in either case, but differs in intensity. In
every field of sensation, the intensity may proceed from the smallest
amount to the greatest amount discernible. In general, the intensity of
the sensation depends on the intensity of the stimulus, though the
condition of the sense-organ as regards fatigue or adaptation to the
stimulus has its effect. It is obvious that a stimulus may be too weak
to produce any sensation; as, for example, a few grains of sugar in a
cup of coffee or a few drops of lemon in a quart of water could not be
detected. It is also true that the intensity of the stimulus may be so
great that an increase in intensity produces no effect on the sensation;
as, for example, the addition of sugar to a solution of saccharine would
not noticeably increase its sweetness. The lowest and highest intensity
points of sensation are called the lower and upper limen, or
threshold, respectively.

By extensity is meant the space-differences of sensations. The touch
of the point of a toothpick on the skin has a different space quality
from the touch of the flat end of a pencil. Low tones seem to have more
volume than high tones. Some pains feel sharp and others dull and
diffuse. The warmth felt from spreading the palms of the hands out to
the fire has a bigness not felt from heating one solitary finger. The
extensity of a sensation depends on the number of nerve endings
stimulated.

The duration of a sensation refers to the time it lasts. This must not
be confused with the duration of the stimulus, which may be either
longer or shorter than the duration of the sensation. Every sensation
must exist for some space of time, long or short, or it would have no
part in consciousness.





Next: Sensory Qualities And Their End-organs

Previous: How We Come To Know The External World



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