Light-spot detection on an illusory figure

We investigated how the detection of a light spot was influenced by the presence of an illusory figure. The light spot was presented off-the-border of the illusory figure, either inside or outside the figure. Detection thresholds were lower when the spot was presented inside the figure than when it was presented outside the figure. This facilitatory effect by the illusory figure may be caused by the process of subthreshold contrast summation that is related to the enhancement of apparent brightness in the illusory figure