UCL News


How card sharps fool the best of us

31 August 2005

A good card trickster can blind you to what is happening before your eyes.

Now a study of how the brain detects changes to visual images has located exactly which area of the brain is responsible.

Past studies … have shown that the parietal cortex is active during visual changes. To find out if this is the part of the brain that actually detects the change, [Professor] Nilli Lavie [UCL Psychology] and colleagues disrupted the parietal cortexes of volunteers while changing the images they were being shown.

The volunteers where shown two images containing four faces and asked to say whether there were any differences between them. When a technique called transcranial magnetic stimulation (TMS) was applied to the right parietal cortex, they failed to notice even a major change such as swapping one of the faces for a different one. TMS induces small currents in specific parts of the brain, temporarily stopping them from operating. …

The findings may help explain how magic tricks work. If the parietal cortex is concentrating on what the magician's left hand is doing, it is not available to notice sleight of hand by the right, Lavie suggests.

'New Scientist'