Illusory Modifications of Area and Apparent Lightness

A white disk when inside a small concentric circle (a display like Delboeuf figure) lookslighter than when surrounded by a larger one. The magnitude of the effect has beenmeasured: PSE are reported for two different measures of the surrounding circle and threedifferent grey backgrounds (EXP. 1a and b). The aim of a second experiment was to comparethe increased lightness effect to the illusory size increment of the central area. Perceived area(EXP. 2a) and lightness magnitudes of a central white disk (diameter: 1.2 cm), surrounded bydifferent circles (diameter: 3, 5, 7, 9 e 11 cm), on a middle grey background, were scaled,according to Pair Comparisons Method. The “distances” of the targets on "area" and"lightness" continua have been determined.