Aristotle’s Illusion (via Tim Hunkin and Lord Kilmarnock)

A while back I was reading the entertainingly gothic ghost story Ferelith by Lord Kilmarnock,  and came across this passage:

At last, after four years of waiting, I stumbled on the opportunity I sought, but as is so often the case with the realisation of human desires, my touchstone proved an illusion. I grasped what had so long eluded me, but it showed me nothing—or next to nothing. It did indeed confirm my theory, but it threw little light on the subject, and gave me no inspiration for my guidance in the future. Jean was in one of her usual trances, I had almost given up the attempt to witness her awakening. I was sitting by her side musing vaguely on the why and wherefore of human existence, and idly turning over the eternal riddle which has no answer. Suddenly I attained Nirvana—that state of double consciousness, of separated sensibility, when the eyes become fixed on a point and yet see nothing. The sensation recalls that produced by crossing two fingers of one hand and passing them down the nose: one feels two slightly indefinite noses, though perfectly aware of the fact that there is but one. Most people have at times been in this state, but for those who have not, the illustration may be useful. The mind is represented by the crossed fingers, the two noses are the detached existences of which that mind becomes conscious. The feeling is not uncommon, though it touches on the borderland of the incomprehensible.

Feeling two noses by using crossed fingers is something I have done quite a lot ever since reading about this in Tim Hunkin’s Almost Everything There is To Know back around 1988. It turns out that this was first described by no less that Aristotle and is known as Aristotle’s Illusion:

A tactile illusion that is created when the eyes are closed, two fingers of one hand are crossed, and a small object such as an acorn is pressed (especially by another person) into the cleft between the tips of the crossed fingers. The sensation is that of touching two objects rather than one. The first written account of it was given by the Greek philosopher Aristotle (384–322bc) in the essay On Dreams in the Parva Naturalia: ‘When the fingers are crossed, one object seems to be two; but yet we deny that it is two; for sight is more authoritative than touch. Yet, if touch stood alone, we should actually have pronounced the one object to be two’ (Chapter 2). Aristotle mentioned it also in Metaphysics: ‘Touch says there are two objects when we cross our fingers, while sight says there is one’ (Book 4, Chapter 6). The explanation for the illusion, apparently overlooked by Aristotle, is that when the fingers are crossed the outsides of two fingers are touched simultaneously, and in ordinary circumstances and past experience that requires stimulation by two separate objects. This explanation was first advanced in Problems, a spurious work often attributed to Aristotle, probably written by one of his followers: ‘When we hold the hand in its natural position, we cannot touch an object with the outer sides of two fingers’ (Book 35, Chapter 10). Further references to the illusion are to be found in Book 31, Chapters 11 and 17 of Problems. Also called Aristotle’s experiment. See also diplaesthesia


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