Research: cutaneous rabbit illusion worked out

7 March 2006

Researchers have cracked the cutaneous rabbit illusion.

Optical illusions show how our visual perceptions can be tricked, but our sense of touch can also be fooled. A classic example is the 'cutaneous rabbit illusion'. Rapid taps to the wrist, then to the elbow, can create an illusion of touches between the two, as if a rabbit has hopped up the arm.

Dr Felix Blankenburg, Professor Jon Driver and colleagues at University College London have now found out what is going on in the brain when this phantom rabbit appears.

Using functional magnetic resonance imaging, they found that the illusion activated those parts of the somatosensory cortex – the area of the brain processing touch signals – that correspond to the points of illusory contact.

The underlying phenomenon remains mysterious. The illusion is similar to other examples where the brain makes assumptions (not always correctly) on the basis of input from the senses. What this study shows is that this kind of 'filling in' is not carried out within brain areas responsible exclusively for conscious processing (it is not 'imagined') but at the cortical level at which the sensation itself is first registered.

External links

• Blankenburg F et al. The cutaneous rabbit illusion affects human primary sensory cortex somatotopically. PLoS Biol 2006;4(3):e69.