Cutaneous rabbit illusion

The cutaneous rabbit illusion (also known as cutaneous saltation) is a tactile illusion evoked by tapping two separate regions of the skin. Many experiments demonstrating the effect have been carried out on the forearm. A rapid sequence of taps delivered first near the wrist, and then near the elbow creates the sensation of sequential taps hopping up the arm from the wrist towards the elbow, although no physical stimulus was applied between the two actual stimulus locations. Similarly, stimuli delivered first near the elbow, then near the wrist, evoke the illusory perception of taps hopping from elbow towards wrist. The illusion was discovered by Frank Geldard and Carl Sherrick of Princeton University, in the early 1970s (Geldard & Sherrick, 1972). They likened the perception to that of a rabbit hopping along the skin, giving the phenomenon its name.

From the moment of its discovery, the illusion has piqued the curiosity of researchers. A study showed that attention directed to one skin location modifies the perceived location of the illusory taps (Kilgard & Merzenich, 1995). Another study showed that the illusory taps are associated with neural activity in the same brain areas that are activated by real taps to the skin (Blankenburg et al., 2006). Nevertheless, the specific neural mechanisms that underlie the rabbit illusion are unknown. Neural models have been proposed by several authors (e.g., Flach & Haggard, 2006), and a recent Bayesian perceptual model replicates the rabbit illusion under the assumption that the brain expects tactile stimuli to move slowly (Goldreich, 2007).

In 2009, researchers of Philips Electronics demonstrated a jacket lined with actuator motors and designed to evoke various tactile sensations while watching a movie. The device takes advantage of the cutaneous rabbit illusion to reduce the number of actuators needed (Jones, 2009).

A group showed that this illusion is not just confined to the “body” (Miyazaki et al., 2010). When subjects held a stick such that it was laid across the tips of their index fingers and received the taps via the stick, they reported sensing the illusory taps along the stick. This suggests that the cutaneous rabbit effect involves not only the intrinsic somatotopic representation but also the representation of the extended body schema that results from body–object interactions.

References

• Geldard, F. and Sherrick, C. (1972). The Cutaneous "Rabbit": a perceptual illusion. Science, 1972 Oct 13;178(57):178-9. PMID 5076909.
• Kilgard, M. P., and Merzenich, M. (1995). Anticipated stimuli across skin. Nature, 1995 Feb 23;373(6516):663. PMID 7854442.
• Blankenburg, F., Ruff, C. C., Deichmann, R., Rees, G. and Driver, J. (2006). Cutaneous rabbit illusion affects human primary sensory cortex somatotopically. PLoS Biology, 4(3):e69. Reprint. Report in News-Medical.net, 1 Mar 2006. Accessed 2008-06-27.
• Flach, R., and Haggard, P. (2006). The Cutaneous Rabbit Revisited. J Exp Psychol Hum Percept Perform, 2006 Jun;32(3):717-32. PMID 16822134.
• Goldreich, D. (2007). A Bayesian perceptual model replicates the cutaneous rabbit and other tactile spatiotemporal illusions. PLoS ONE, 2007 Mar 28;2(3):e333. PMID 17389923. Reprint. Accessed 2008-06-27.
• Jones, Willie D. (2009). Jacket Lets You Feel the Movies, IEEE Spectrum Online, 18 March 2009
• Miyazaki, M., Hirashima, M., and Nozaki D. (2010). The "Cutaneous Rabbit" Hopping out of the Body. The Journal of Neuroscience, 2010 Feb 3;30(5):1856-1860. PMID 20130194. Reprint,Report in New Scientist.