Apparent brightness enhancement in the Kanizsa square with and without illusory contour formation

The perceived strength of darkness enhancement in the centre of surfaces surrounded or not surrounded by illusory contours was investigated as a function of proximity of the constituent elements of the display and their angular size. Magnitude estimation was used to measure the perception of the darkness phenomenon in white-on-grey stimuli. Darkness enhancement was perceived in both types of the stimuli used, but more strongly in the presence of illusory contours. In both cases, perceived darkness enhancement increased with increasing proximity of the constituent parts of the display and with their angular size. These results suggest that the occurrence of darkness (or brightness) enhancement phenomena in the centre of the displays is not directly related to illusory contour formation.