Abstract
The electrical activities of the brain, especially the contingent negative variation (CNV) and the sensory evoked potentials (SEP), were studied under two different conditions of stimulus presentation in the simple reaction experiment. In one condition, both preparatory and reaction stimuli were presented at random by the experimenter. In another, a preparatory stimulus was presented contingent upon subject's spontaneous response, which was followed after a given foreperiod by a reaction stimulus. Main findings were as follows; (1) Amplitude of the CNV was larger in the former than in the latter. (2) The late positive component of the SEP showed larger amplitude in the former than in the latter.
