Neuron 59, 561–567 (2008)

Credit: M. PESSIGLIONE G. GEORGIOU/PANOS

Humans can learn to assess risks on the basis of visual hints they are not aware of seeing.

Mathias Pessiglione of the Pitié-Salpêtrière Hospital in Paris and his colleagues repeatedly showed 20 subjects abstract symbols as they played a gambling game. Each symbol presentation involved one of three choices and was followed by a 'masking image' in a series that flickered so fast that the subjects could not consciously perceive the symbol shapes. The subjects were told that the symbols were associated with winning or losing, and then allowed to gamble.

The subjects won more than they lost, indicating that their brains recognized the unperceived symbols and learned to associate them with reward or punishment. Functional neuroimaging showed that the mechanism involves the ventral striatum, a brain area associated with assessing reward value (pictured).