Touch illusion

Touch illusions are illusions that exploit the sense of touch.

Examples
An example of a 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 with index and middle finger crossed along an edge feels like two parallel edges.

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 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 of 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.

Another is a physiological illusion where with one hand immersed in cold water and the other in hot and then both in lukewarm, the lukewarm water will feel both hot and cold.

If a person exposes their forearm and closes their eyes or turns their head in the opposite direction while a second person slowly trace 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.

When touching paradoxical objects, you can feel a hole when actually you are touching a bump (Robles-De-La-Torre & Hayward 2001). These "illusory" objects can be used to create tactile "virtual objects" (see the MIT Technology Review article 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.