抄録
The spatial summation properties on background field and in dark were investigated by applying the spatial double stimuli method, in which summation indices were obtained for various separations between two stimuli. For some subjects summation index curves, which plotted summation index as a function of separation, showed diphasic nature having inhibitory interaction at separation of 5.2' when the background luminance was 8 cd/m2. The curves from other subjects, however, showed monophasic nature. When background luminance was reduced to zero, the summation index curves of the subjects who showed the diphasic nature changed to monophasic, while those of other subjects did not change. It was concluded when the adapting level was reduced from 8 cd/m2 to 0 cd/m2 the inhibitory connection of the spatial summation property disappeared in contrast to no change of the excitatory connection.
