Two experiments were conducted to examine how additional dotted lines and peripheral stimulus to the caf$grave{e}$ wall illusion affect on the degree of perceived tilt (amount of illusion) and confidency of illusionary perception. The experiment 1 tested the effects of adding mortar (solid line) and bright contrast dotted lines to the borderline of 3 layers of blocks, which are consisted of black and white blocks. On the experiment 2, effects of adding peripheral stimulus on caf$grave{e}$ wall illusion were tested. The results of experiment 1 showed that adding dotted line on the borderline mortar between blocks has additive effects on confidency of illusory perception. However, no effect on perceived amount of illusion was noted. On the other hand according to the results of experiment 2, adding blocks did increase amount, but not confidency of illusory perception. These results imply that the perception of caf$grave{e}$ wall illusion is related with response of orientation selective neurons.