We cannot discriminate the one pressure point from the other.

But if we move the point of a pencil to and fro from one point to the other we perceive distinctly the movement in spite of the fact that it is a movement between two end points which could not be discriminated.

It is wholly characteristic that the experimenter in every field of sensations, visual or acoustical or tactual, often finds himself before the experience of having noticed a movement while he is unable to say in which direction the movement occurred.
We are familiar with the illusions in which we believe that we see something which only our imagination supplies.

If an unfamiliar printed word is exposed to our eye for the twentieth part of a second, we readily substitute a familiar word with similar letters.

Everybody knows how difficult it is to read proofs.