I have already remarked that in the mental life of the adult perfectly new sensations never occur.

At the same time, comparatively novel impressions sometimes arise.

Parts of the sensitive surface of the body which rarely undergo stimulation are sometimes acted on, and at other times they receive partially new modes of stimulation.

In such cases it is plain that the process of classing the sensation or recognizing it is not completed.

It is found that whenever this happens there is a tendency to exaggerate the intensity of the sensation.