The strength of chromatic after-effect was studied using the filling-in after-effect image illusion (Van Lier et al.). In our experiments, two stimuli, each consisting of round and sharp-edged overlapping chromatic shapes, were presented to the subjects for 1.2 s on both sides of the fixation point. After that the empty shapes of the stimuli appeared for 0.6 s, and in the next 0.6 s changed the orientation on both sides of the fixation point thus changing the after-effect color from side to side. The subjects made judgments about the strength of the perceived after-effect on a ten-grade scale for different color pairs. The color of one stimulus was kept constant, while the color of the other was changed; as a result of color changes of both stimuli 192 color pairs in total were formed. Some of them were found to arouse a powerful sensation of the after-effect with a color not directly arranged on the opposite axis of chromaticity diagram. Blue and yellow colors were valued as creating the most pronounced after-effect.
