In order to examine some aspects of the function of the sensory-motor cortex in voluntary movements, the selective reaction was studied against photic stimulation.<BR>An experimental board was constracted, on which there were 12 lamps equally spaced on a circle (radius 32cm) and a key at the center of the circle.<BR>An electrical signal appeared when a lightening lamp or the lamp at the opposite position relative to the lightening one touched. Ten healthy male and female subjects were selected, whose age ranged from 19 to 32. The subject stood in front of the board, softly touched the key with his/her Digitus Medius and looked at the key. The surrounding lamps were imaged on the field of indirect vision. When one of the lamps was lightened, the subject touched as quickly as possible the lightening lamp (named this action as “catching action”) or the opposite lamp (“avoiding action”), following the initial instruction. The following three cases were studied : (a) 2 directions ; one of the two lamps (NO. 1 & 7) was lightened, (b) 4 directions ; one of the four lamps (No. 1, 4, 7 & 10) was lightened and (c) 12 directions ; one of 12 lamps was lightened. This order was assumed to be in the increasing load condition. The EMG was also recorded, so that we could measure the following five characteristic time<BR>1. Total Time (TT), the time interval between the moment of lightening of a lamp (light stimulation) and the moment of touching the target lamp.<BR>2. Reaction Time (RT), the time interval from the beginning if the light stimlation to the release of the finger from the key.<BR>3. Muscle Contraction Time (MCT), the time interval from the release of the finger from the key to the moment of touching the target lamp.<BR>4. Premotor Time (PMT), the time interval from the beginning of the light stimulation to the onset of discharge on EMG.<BR>5. Motor Time (MT), the time interval from the onset of discharge on EMG to the release of the finger from the key.<BR>The following results were obtained ;<BR>1) In both cases of the dominant and non-dominant hands, TT, RT and MCT were longer in the avoiding than in the catching actions. This trend was independent of the above three load conditions.<BR>2) In both catching and avoiding actions, most of the experimental results distributed nearly normally on the histograms of frequency versus characteristic time<BR>3) When the load condition was changed from (a) to (c), RT and PMT clearly shortened but no appreciable change in MCT was observed in the catching action, while RT showed a trend to lengthen in the avoiding action.