Illusory dilatation of square surfaces

The aim of the present research was to study illusory dilatation of surfaces isolating some factors contributing to this phenomenon. A series of displays (8.5 cm x 8.5 cm) was prepared: a white square card and five square cards with a uniform pattern of black dots, increasing gradually. The displays were presented to two different groups of subjects, according to the method of paired comparisons and according to the method of limits (under conditions of reduced viewing) respectively. The subjects were asked to evaluate the relative magnitude of the displays. The textured cards significantly differed from the white standard and also among themselves. Up to a threshold, as the dots increase, the surfaces expand as well.