Thus, when a feeling resulting from a disturbance in the optic nerve is interpreted as one of external light vaguely felt to be acting on the eye, or one resulting from some action set up in the auditory fibre as a sensation of external sound vaguely felt to be entering the ear, we see that the error of localization is a consequence of the other error already characterized.
As I have already observed, an excitation of a nerve at any other point than the peripheral termination, occurs but rarely in normal life.

One familiar instance is the stimulation of the nerve running to the hand and fingers, by a sharp blow on the elbow over which it passes.

As everybody knows, this gives rise to a sense of pain at the _extremities_ of the nerve.

The most common illustration of such errors of localization is found in subjective sensations, such as the impression we sometimes have of something creeping over the skin, of a disagreeable taste in the mouth, of luminous spots floating across the field of vision, and so on.

The exact physiological seat of these is often a matter of conjecture only; yet it may safely be said that in many instances the nervous excitation originates at some point considerably short of its peripheral extremity: in which case there occurs the illusion of referring the impressions to the peripheral sense-organ, and to an external force acting on this.
The most striking instances of these errors of localization are found in abnormal circumstances.