Extinction is the failure to respond to a novel or meaningful sensory stimulus on one side when a homologous stimulus is given simultaneously to the contralateral side (i.e., double simultaneous stimulation); it is sometimes called "suppression." The stimuli may be visual, auditory, or tactile, e.g., asking the patient to say which hand is touched when the eyes are shut. It is important to show that the patient responds appropriately to each hand being touched individually, but then neglects one side when both are touched simultaneously.
More subtle defects may be tested using simultaneous bilateral heterologous (asymmetrical) stimuli, although it has been shown that some normal individuals may show extinction in this situation.
A motor form of extinction has been postulated, manifesting as increased limb akinesia when the contralateral limb is used simultaneously.
The presence of extinction is one of the behavioral manifestations of neglect, and most usually follows nondominant (right) hemisphere lesions.
There is evidence for physiological interhemispheric rivalry or competition in detecting stimuli from both hemifields, which may account for the emergence of extinction following brain injury.
Fink GR, Driver J, Rorden C, Baldeweg T, Dolan RJ. Neural consequences of competing stimuli in both visual hemifields: a physiological basis for visual extinction. Annals of Neurology 2000; 47: 440-446