waves in the intervening air, ready to be translated through the machinery of
nerves and brain into the beautiful tones and melodies and harmonies of the
mind. And so with all other sensations.
The Three Sets of Factors.—What exists outside of us therefore is a stimulus,
some form of physical energy, of a kind suitable to excite to activity a certain
end-organ of taste, or touch, or smell, or sight, or hearing; what exists within us
is the nervous machinery capable of converting this stimulus into a nerve current
which shall produce an activity in the cortex of the brain; what results is the
mental object which we call a sensation of taste, smell, touch, sight, or hearing.
2. 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