The Mind and Its Education - George Herbert Betts

Dependence of the Mind on the Senses.—Only as the senses bring in the
material, has the mind anything with which to build. Thus have the senses to act
as messengers between the great outside world and the brain; to be the servants
who shall stand at the doorways of the body—the eyes, the ears, the finger tips—
each ready to receive its particular kind of impulse from nature and send it along
the right path to the part of the cortex where it belongs, so that the mind can say,
"A sight," "A sound," or "A touch." Thus does the mind come to know the
universe of the senses. Thus does it get the material out of which memory,
imagination, and thought begin. Thus and only thus does the mind secure the
crude material from which the finished superstructure is finally built.