Touch illusion

Touch illusions are illusions that exploit the sense of touch. Some touch illusions require active touch (e.g., movement of the fingers or hands), whereas others can be evoked passively (e.g., with external stimuli that press against the skin).

Examples

*One of the best known passive tactile illusions is the cutaneous rabbit illusion, in which a sequence of taps at two separated skin locations results in the perception that intervening skin regions were also tapped.

*If a person exposes their forearm and closes their eyes or turns their head in the opposite direction while a second person slowly traces a finger from the wrist upward to the crook of the elbow, many people are unable to say when the crease of their elbow is being touched.

*If one hand is immersed in cold water and the other in hot for a minute or so, and then both hands are placed in lukewarm water, the lukewarm water will feel hot to the hand previously immersed in cold water, and cold to the hand previously immersed in hot water.

*An example of an active touch illusion is the contingent after-effect. When the thumb and forefinger are slid repeatedly along the edge of a wedge, a rectangular block then handled in the same manner will feel deformed.

*Moving the crossed index and middle finger along an edge evokes the perception of two parallel edges. Similarly, if a person crosses their index and middle finger and then rolls a marble between the tips of the fingers, two marbles are perceived.

*If a person wears a baseball cap for a long period of time and then takes it off, it may still be felt.

*If a person turns their tongue upside down, and runs their finger along the front, it will feel like the finger is moving in the opposite direction.

*If a person pushes outwards with their hands against something for a while, then stops, it will feel as if there is something stopping the person's hands from closing together. Similarly, if a person pulls outwards with their arms, for example pulling their pants outwards, then stops, it will feel as if something is keeping their hands from staying at their sides.

*If a person is lying on his/her stomach with arms stretched in front and another person raises his/her arms about 2 feet off the ground and holds them there for approximately one minute, with the person on the ground having his/her eyes closed and head hanging, then slowly lowers the arms to the ground, it will feel as if the arms are going below the ground.

*When touching [http://www.roblesdelatorre.com/gabriel/haptics.htm paradoxical objects] , you can feel a hole when actually you are touching a bump ( [http://www.roblesdelatorre.com/gabriel/GR-VH-Nature2001.pdf Robles-De-La-Torre & Hayward 2001] ). These "illusory" objects can be used to create tactile "virtual objects" (see the MIT Technology Review article [http://www.technologyreview.com/read_article.aspx?id=17363&ch=biotech&sc=&pg=1 The Cutting Edge of Haptics] ).

*If two people join their opposite hands and one slides his index and thumb over two joined fingers he will feel the other finger like it was one of his.

References

*cite journal|author=Flanagan, J.R., Lederman, S.J.|url=http://brain.phgy.queensu.ca/flanagan/papers/FlaLed_NAT_01.pdf|title=Neurobiology: Feeling bumps and holes, News and Views|journal=Nature|volume=412|issue=6845|pages=389–91|year=2001 | doi = 10.1038/35086674
*
*cite journal|author=Robles-De-La-Torre G. & Hayward V.|url=http://www.roblesdelatorre.com/gabriel/GR-VH-Nature2001.pdf|title=Force Can Overcome Object Geometry In the perception of Shape Through Active Touch|journal= Nature|volume=412|issue=6845|pages=445–8|year=2001 | doi = 10.1038/35086588
*cite journal|author=Robles-De-La-Torre G.|url=http://www.roblesdelatorre.com/gabriel/GR-IEEE-MM-2006.pdf|title=The Importance of the Sense of Touch in Virtual and Real Environments|journal=IEEE Multimedia|volume=13|issue=3, Special issue on Haptic User Interfaces for Multimedia Systems|pages=24–30|year=2006 | doi = 10.1109/MMUL.2006.69

External links

* [http://www.roblesdelatorre.com/gabriel/haptics.htm Paradoxical objects.] Touch illusions created with virtual reality technology.
* [http://www.technologyreview.com/read_article.aspx?id=17363&ch=biotech&sc=&pg=1 The Cutting Edge of Haptics] Using touch illusions to create virtual objects with sharp borders. An article in MIT's Technology review by Duncan Graham-Rowe.