Listening with one or two hemispheres: verbal dichotic testing after intracarotid barbiturate injection.

A verbal dichotic test was given to 16 patients during right or left hemisphere narcosis induced by intracarotid barbiturate injection (Wada's procedure). During right hemisphere narcosis patients did not repeat left ear words. This demonstrates an intrahemispheric competition within the left hemisphere at the detriment of left ipsilateral ear words. After left dominant hemisphere narcosis, when aphasia had apparently disappeared, patients temporarily did not repeat right ear words. This suggests that, during this critical time period, two competitive processes took place. First the right hemisphere selected the left ear words by an intrahemispheric competition. Second it imposed them on the recovering left hemisphere at the detriment of right ear words, because of an interhemispheric competition.