The World as Percept 65whether the excitation occurs through what we call light,
through mechanical pressure, or through an electrical cur-
rent impinging on the nerve. On the other hand, the same
external stimuli evoke different percepts in the different
senses. It appears to follow from this that our senses can
transmit only what occurs within them and transmit noth-
ing from the outer world. The senses determine the per-
cepts according to their nature.
Physiology shows that there can also be no direct
knowledge of what effect objects have within our sense
organs. When physiologists follow the processes in our
own body, they find the effects of external motion already
transformed within the sense organs in the most various
ways. We see this most clearly in the eye and the ear. Both
are very complicated organs, which fundamentally alter
an external stimulus before bringing it to the correspond-
ing nerve. From the peripheral nerve ending, the already
modified stimulus is now led on to the brain. Here, the
central organs must in turn be stimulated. From this, the
conclusion is drawn that the external process undergoes a
series of transformations before coming to consciousness.
What goes on in the brain is connected to the external pro-
cess through so many intermediate processes that we can-
not imagine any similarity between them. What the brain
then finally transmits to the soul are neither external pro-
cesses, nor processes in the sense organs, but only pro-
cesses within the brain. Yet even these the soul does not
perceive directly. What we ultimately have in conscious-
ness are not brain processes at all, butsensations. My sen-
sation of red has no similarity to the process occurring in