Page:Mind (Old Series) Volume 12.djvu/18

THE PERCEPTION OF SPACE. (l.) 5 In the skin itself there is a vague form of projection into the third dimension to which Hering has called attention. 1 " Heat is not felt only against the cutaneous surface, but when com- municated through the air may appear extending more or less out from the surface into the third dimension of surroundiog space. . . . We can de- termine in the dark the place of a radiant body by moving the hand to and fro, and attending to the fluctuation of our feeling of warmth. The feeling itself, however, is not projected fully into the spot at which we localise the hot body, but always remains in the neighbourhood of the hand." The interior of one's mouth-cavity feels larger when ex- plored by the tongue than when looked at. The crater of a newly-extracted tooth, and the movements of a loose tooth in its socket, feel quite monstrous. A midge buzzing against the drum of the ear will often seem as big as a butterfly. The spatial sensibility of the tympanic membrane has hitherto been very little studied, though the subject will well repay much trouble. If we approach it by introducing into the outer ear some small object like the tip of a rolled- up tissue paper lamplighter, or the end of a wooden tooth- pick made soft between the teeth, we are surprised at the large radiating sensation which its presence gives us, and at the sense of clearness and openness which comes when it is removed. It is immaterial to inquire whether the far- reaching sensation here be due to actual irradiation upon distant nerves or not. We are considering now, not the objective causes of the spatial feeling, but its subjective varieties, and the experiment shows that the same object gives more of it to the inner than to the outer cuticle of the ear. The tympanic membrane is furthermore able to render sensible differences in the pressure of the external atmo- sphere, too slight to be felt as noise. If the reader will sit with closed eyes and let a friend approximate some solid various organs by setting in motion, by a sort of reflex action, the set of muscles which belong to them. One can ask, then, with what particular muscular contraction the sense of strained attention in the effort to recall something is associated ? On this question my own feeling gives me a decided answer ; it comes to me distinctly not as a sensation of tension in the inside of the head, but as a feeling of strain arid contraction in the scalp, with a pressure from outwards in over the whole cranium, un- doubtedly caused by a contraction of the muscles of the scalp. This harmonises very well with the expressions, sich den Kopf zerbrechen, den Kopf zusammennehmen. In a former illness when I could not endure the slightest effort after continuous thought, and had no theoretical bias on this question, the muscles of the scalp, especially those of the back-head, assumed a fairly morbid degree of sensibility whenever I tried to think." (Elem. der Psychophysik, ii. 490-91.) 1 Hermann's Handb. der Physiologic, iii. 2, p. 436.