[450] [The left and sound eye is here supposed covered. If both eyes look at the same field there are double images which still more perplex the judgment. The patient, however, learns to see correctly before many days or weeks are over.—W. J.]
[451] Alfred Graefe, in Handbuch der gesammten Augenheilkunde, Bd. vi. pp. 18-21.
[452] Professor G. E. Müller (Zur Grundlegung der Psychophysik (1878), p. 318,) was the first to explain the phenomenon after the manner advocated in the text. Still unacquainted with his book, I published my own similar explanation two years later.
Professor Mach in his wonderfully original little work 'Beiträge zur Analyse der Empfindungen,' p. 57, describes an artificial way of getting translocation, and explains the effect likewise by the feeling of innervation. "Turn your eyes," he says, "as far as possible towards the left and press against the right sides of the orbits two large lumps of putty. If you then try to look as quickly as possible towards the right, this succeeds, on account of the incompletely spherical form of the eyes, only imperfectly, and the objects consequently appear translocated very considerably towards the right. The bare will to look rightwards gives to all images on the retina a greater rightwards value, to express it shortly. The experiment is at first surprising."—I regret to say that I cannot myself make it succeed—I know not for what reason. But even where it does succeed it seems to me that the conditions are much too complicated for Professor Mach's theoretic conclusions to be safely drawn. The putty squeezed into the orbit, and the pressure of the eyeball against it must give rise to peripheral sensations strong enough, at any rate (if only of the right kind), to justify any amount of false perception of our eyeball's position, quite apart from the innervation feelings which Professor Mach supposes to coexist.
[453] An illusion in principle exactly analogous to that of the patient under discussion can be produced experimentally in anyone in a way which Hering has described in his Lehre von Binocularen Sehen, pp. 13-14. I will quote Helmholtz's account of it, which is especially valuable as coming from a believer in the Innervationsgefühl: "Let the two eyes first look parallel, then let the right eye be closed whilst the left still looks at the infinitely distant object a. The directions of both eyes will thus remain unaltered, and a will be seen in its right place. Now accommodate the left eye for a point f a, only very near. The position of the left eye and its optical axis, as well as the place of the retinal image upon it... are wholly unaltered by this movement. But the consequence is that an apparent movement of the object occurs—a movement towards the left. As soon as we accommodate again for distance the object returns to its old place. Now what alters itself in this experiment is only the position of the closed right eye: its optical axis, when the effort is made to accommodate for the point f, also converges towards this point.... Conversely it is possible for me to make my optical axes diverge, even with closed eyes, so that in the above experiment the right eye should turn far to the right of a. This divergence is but slowly reached, and gives me therefore no illusory movement. But when I suddenly relax my effort to make it, and the right optical axis springs back to the parallel position, I immediately see the object which the left eye fixates shift its position towards the left. Thus not only the position of the seeing eye a, but also that of the closed eye b, influences our judgment of the direction in which the seen object lies. The open eye remaining fixed, and the closed eye moving towards the right or left, the object seen by the open eye appears also to move towards the right or left" (Physiol. Optik, pp. 607-8.)
[454] Beiträge zur Analyse der Empfindungen, p. 65.
[455] P. 68.
[456] I owe the interpretation in the text to my friend and former student, Mr. E. S. Drown, whom I set to observe the phenomenon before I had observed it myself. Concerning the vacillations in our interpretation of relative motion over retina and skin, see above, [p. 173].
Herr Münsterberg gives additional reasons against the feeling of innervation, of which I will quote a couple. First, our ideas of movement are all faint ideas, resembling in this the copies of sensations in memory. Were they feelings of the outgoing discharge, they would be original states of consciousness, not copies; and ought by analogy to be vivid like other original states.—Second, our unstriped muscles yield no feelings in contracting, nor can they be contracted at will, differing thus in two peculiarities from the voluntary muscles. What more natural than to suppose that the two peculiarities hang together, and that the reason why we cannot contract our intestines, for example, at will, is, that we have no memory-images of how their contraction feels? Were the supposed innervation-feeling always the 'mental cue,' one doesn't see why we might not have it even where, as here, the contractions themselves are unfelt, and why it might not bring the contractions about. (Die Willenshandlung, pp 87-8.)
[457] Revue Philosophique, xxiii. 442.