Cutaneous Rabbit Illusion

The cutaneous rabbit illusion is a tactile perceptual illusion in which a short, rapid sequence of taps delivered to only two or three widely separated points on the skin, such as the wrist and a point further up the forearm, is perceived instead as a smooth, evenly spaced series of taps hopping progressively along the entire stretch of skin in between, as though a small animal were hopping up the arm one step at a time. The psychologists Frank Geldard and Carl Sherrick first described the effect in a 1972 study, and its name reflects this vivid subjective hopping sensation even though no physical stimulation whatsoever is actually delivered to most of the intervening skin. Researchers have used the illusion as an important tool for studying how the nervous system constructs a coherent perceptual experience of location and timing from limited discrete sensory input, since the perceived position of each illusory tap is influenced not only by where and when it was actually delivered but also by the location and timing of taps that have not yet even occurred, implying that the brain integrates a short window of upcoming sensory information before finalizing where earlier stimulation seemed to occur. The cutaneous rabbit illusion remains a frequently cited example in discussions of how perception is an active, temporally extended process of inference rather than a simple, instantaneous readout of raw sensory signals.