nce of the
car. Responding to a stimulus presented to one sense by perceiving a
fact which could only be directly presented to another sense is
exemplified also by such common expressions as that the stone "looks
heavy", or that the bell "sounds cracked". or that the jar of fruit
"smells sour". Sense perception, then, is responding to a stimulus by
knowing some fact indicated by it either directly or indirectly.
Perception that is not sense perception occurs when the fact perceived
is not even indirectly presented to the senses at the moment. The fact
is then presented by recall; yet the fact in question is not recalled.
Recall not only gives you facts previously perceived, but may provide
the data, the stimulus, for fresh perception. Putting together two
recalled facts, you may perceive a further fact not previously known.
Remembering that you took your umbrella to the office this morning in
the rain, that it was fine when you left the office, and that you
certainly did not have the umbrella when you reached home, you
perceive that you must have left it at the office. Reading in the
paper of preparations for another polar expedition, and remembering
that both poles have already been discovered, you perceive that there
is something more in polar exploration than the mere race for the
pole. Perception of this sort amounts to "reasoning", and will be
fully considered in another chapter, while here we shall focus our
attention on sense perception.

{423}

The Difference Between Perception and Sensation

If sense perception is a response to a sensory stimulus, so is
sensation, and the question arises whether there is any genuine
difference between these two. In the instance of "hearing the street
car", the difference is fairly obvious; hearing the noise is
sensation, while knowing the street car to be there is perception.

Sensation is the first response aroused by a stimulus, or at least the
first response that is conscious. Perception is a second response,
following the sensation, and being properly a direct response to the
sensation, and only an indirect response to the physical stimulus. The
chain of events is: stimulus, response of the sense organ and sensory
nerve, first cortical response which is sensation, second cortical
response which is perception.

Conscious sensation is the response of the part of the cortex that
first receives the nerve current from the sense organ stimulated, the
response of the "senso