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Descartes says that the senses deceive us. I agree for all senses, except for the tactile sense (i.e., when you touch something).
It's clear there are optical illusions, but there appear to be no tactile illusions. When we touch something, we know or we don't know (and know that we don't know) information about that thing. I can't remember being mistaken by my sense of touch.
Can anybody give an example of when the tactile sense deceives us?
Touch is just another form of sensory input subject to imperfect reading of the world like any other sense. http://en.wikipedia.org/wiki/Tactile_illusion
The whole phantom limb phenomenon involves massive deception, not sure whether this fits in your categorization of "tact". (Phantoms in the Brain: Probing the Mysteries of the Human Mind - fascinating and unexpected)
It's interesting that the sense of touch is a main element in a parable about the fallibility of senses and knowledge: https://en.wikipedia.org/wiki/Blind_men_and_an_elephant
Temperature may be a good example. If you give someone a metal bar and a book, which both have the same temperature, say 15°C, people will say the metal bar feels colder than the book. It's different from an optical illusion in the sense that there is a real, physical explanation, namely that (a) the temperature we feel is the temperature of our hand, not of the object we're holding and (b) the metal bar is a thermal conductor (it will drop the temperature of our hand faster), while the book is a thermal insulator (it will drop the temperature of our hand only very slowly).
Videos that illustrate the point I made in a very clear manner:
Yes, cross your two middle fingers. Then close your eyes and rub your nose between the V made by your two crossed fingers. You will have a sense of having two noses.
Way back when I was a child, I watched Mr. Wizard on TV. He had a neat experiment to demonstrate how touch can deceive. He took a ruler, and made a cardboard slide that goes around it. At one end of the ruler, he put a pin, and he attached one to the slide, so that he could vary the distance between the pins.
He got his subject to hold out her arm and he lightly tapped the pins against the inside of her arm, an inch apart at first, and asked her how many pins she felt: two, of course. He then decreased the distance until he got within the distance we have between sensory nerves in the skin. At that distance, suddenly one pin vanished, and the woman helping him only felt one pin. (he then went on to repeat the test on other parts of the body, such as the lips, to show that different parts of the body have sensory nerves closer together than others).
Also consider the fun experiment where you stand in a doorway and press your arms out against the sides. Spend a minute like this, during which your body is processing its tactile inputs and making its best guesstimates as to what your body is doing. When you step out, your arms rise. You end up confusing the sensors in the body which detect muscle length, which are a fundamental part of the kinesthetics that tactile input lets us use.
Many internal martial arts take advantage of touch's ability to deceive, allowing their opponent to overextend because their opponent thinks they're in one position when they're actually in another.
Finally, saving the best for last, why not just take the lesson from the best: Penn and Teller.
In opposite, in a optical illusion, the information itself, given by the eye, is wrong (not the interpretation).
that's incorrect, imho. eyes give you information as they receive it. it's your mind interpretation that's wrong. that's true for any sense - you get the raw information, and then you mind misinterpret it, based on your previous experience
just one interesting example from the psychology - afaik, newborn cannot distinguish separate objects in that he see, he even can't focus on them! it needs some experience to start perfrom these activities, and that means that unless you don't focus and don't try to recognize separate things, you are interpreting information your eyes can give you
Yes, similar to 'The Doctor's' answer above but more to the "point": The following is called "Aristotle's Illusion." This "tactile illusion" occurs when the eyes are closed, and the index finger is crossed under the finger next to it. Then the point of a pen or a pencil is placed directly into the cleft between the tips of the crossed fingers. The sensation is that of touching two objects rather than one. Try it. You can do this with or without another person. You will find, since your eyes are closed, another person can more easily place the point directly into the cleft... If you would like an explication / explanation you can find it on the "Merleau-Ponty and Phenomenology' fb group page. Seeing and touching "overhang" each other more than any other senses. All or most of what we see is already from afar inscribed in our tactile field. Likewise all we touch reaches over into vision insofar as sleek and rough surfaces are available to the visual field even while tacit. (As indeed the second layer of meaning - "vision" - indicates.) Finally, (this is no joke) ALL vision is 'TELE-vision,' literally!
