This is one of the most curious of all phenomena occurring in the hypnotic state. If a person who is hypnotized is told to open his eyes he will do so, and seeing, will perceive only as the operator may suggest. Prof. James mentions some very interesting experiments, which prove that blindness which can be induced by suggestion is purely psychic, and not due to any effect directly upon either the centre of sight in the brain or locally upon the eye. The hypnotized subject will become psychically blind at the operator's will. If a line is made upon a clean blackboard, the hypnotized subject, if commanded to do so, will tell you that the blackboard is still a blank. Place a number of lines in any position you please around the first one. The hypnotized subject will still insist that the line you first made upon the blackboard is not there. Prof. James argues that the fact of the hypnotized subject refusing to recognize the existence of a line, is an evidence that the subject saw the line, but that his consciousness refused to recognize its existence.

The following are Prof. James' own words: "Make a stroke on a paper or blackboard, and tell the subject it is not there, and he will see nothing but the clean paper or board, Next, he not looking, surround the original stroke with other strokes exactly like it, and ask him what he sees. He will point out one by one the new strokes, and omit the original one every time, no matter how numerous the new strokes may be, or in what order they are arranged. Similarly, if the original single line, to which he is blind, be doubled by a prism of sixteen degrees placed before one of his eyes (both being kept open), he will say that he now sees one stroke, and point in the direction in which lies the image seen through the prism.

"Another experiment proves that he must see it in order to ignore it. Make a red cross, invisible to the hypnotic subject, on a sheet of white paper, and yet cause him to look fixedly at a dot on the paper on or near the red cross; he will, on transferring his eye to the blank sheet, see a bluish-green after-image of the cross. This proves that it has impressed his sensibility. He has felt but not perceived it. He had actually ignored it, refused to recognize it, as it were."

I trust the reader will bear in mind these two experiments, as they will throw much light upon the theory which later I shall advance, to explain the physiology of the hypnotic state.