The Pinocchio illusion is an illusion

Illusion

An illusion is a distortion of the senses, revealing how the brain normally organizes and interprets sensory stimulation. While illusions distort reality, they are generally shared by most people....

 that one's nose

Human nose

The visible part of the human nose is the protruding part of the face that bears the nostrils. The shape of the nose is determined by the ethmoid bone and the nasal septum, which consists mostly of cartilage and which separates the nostrils...

 is growing longer, as happened to the literary character Pinocchio

Pinocchio

The Adventures of Pinocchio is a novel for children by Italian author Carlo Collodi, written in Florence. The first half was originally a serial between 1881 and 1883, and then later completed as a book for children in February 1883. It is about the mischievous adventures of Pinocchio , an...

 when he told a lie. It is an illusion of proprioception

Proprioception

Proprioception , from Latin proprius, meaning "one's own" and perception, is the sense of the relative position of neighbouring parts of the body and strength of effort being employed in movement...

, reviewed by Lackner (1988).

To experience the illusion, a vibrator

Vibrator (mechanical)

A vibrator is a mechanical device to generate vibrations. The vibration is often generated by an electric motor with an unbalanced mass on its driveshaft.There are many different types of vibrator...

 is applied to the biceps

Biceps

Biceps may refer to:*Biceps brachii muscle, a muscle located on the inside of the upper arm*Biceps femoris muscle, one of the hamstring muscles of the back of each thigh*Biceps , a point in a metrical pattern...

 tendon while one holds one's nose with the hand of that arm. The vibrator stimulates muscle spindle

Muscle spindle

Muscle spindles are sensory receptors within the belly of a muscle, which primarily detect changes in the length of this muscle. They convey length information to the central nervous system via sensory neurons. This information can be processed by the brain to determine the position of body parts...

s in the biceps that would normally be stimulated by the muscle's stretching, creating a kinesthetic illusion that the arm is moving away from the face. Because the fingers holding the nose are still giving tactile information of being in contact with the nose, it appears that the nose is moving away from the face too, in a form of perceptual capture.

The illusion involves activity in the parietal cortex of the brain

Brain

The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...

 responsible for integrating information from different parts of the body (e.g., Ehrsson, Kito, Sadato, Passingham, & Naito, 2005). Distortions of the size of parts of the body can sometimes occur spontaneously, through application of psychedelic

Psychedelic drug

A psychedelic substance is a psychoactive drug whose primary action is to alter cognition and perception. Psychedelics are part of a wider class of psychoactive drugs known as hallucinogens, a class that also includes related substances such as dissociatives and deliriants...

 chemicals or during epilepsy or migraine auras.