The influence of simple lateralized visual warning stimuli on decision and movement time (jump reaction) for a centrally presented choice reaction stimulus was examined in 20 normal healthy subjects. Without warning the right hand (left hemisphere) showed faster decision times for the choice reaction stimuli. After presentation of the lateralized warning stimulus this difference was no longer present while for both hands there was improvement after warning. This indicates that the left hand (right hemisphere) showed a more pronounced improvement of decision time following the warning stimulus than the right hand. In contrast, the number of errors (false positives) increased after LVF stimulation. Experimental conditions had no influence on movement time at all. It was concluded that the complexity of the lateralized warning stimulus and not of the centrally presented reaction stimulus determines hemispheric activation dominance.