The present study was conducted to investigate the relative cognitive abilities of the right and left hemispheres. A perceptual and memory functions on the occurrence of a laterality effect were examined in two sets of experiments. In both experiments, standard stimuli (arc) were presented at the center of the visual field and successively comparison stimuli (circle) were exposed tachistoscopically in the right or the left visual field. The subject's task was to report whether the standard were a part of the comparison or not. The results of both experiments show that the left visual field condition is superior to the right visual field condition. These findings suggest that (1) the right hemisphere is more specialized in performing a higher cognitive task such as inferential thought than the left hemisphere, (2) Both memory and perceptual factors contribute to a laterality effect in the present task.