DISCRIMINATION OF THE SHAPE OF THE MASKED INDUCING FIGURE PRECEDES PERCEPTION OF THE ILLUSORY TRIANGLE

Using the Kanizsa triangle in a free-inspection paradigm, Gellatly has shown that subjects report seeing an illusory triangle while apparent ly not phenomenally aware of the inducing areas. It is argued that Gel latly's procedure may induce response processes which camouflage early sensory processes. By forcing subjects to choose between two response alternatives, it was shown that when they could just perceive the ill usory triangle, they could also correctly discriminate the shape of th e inducing elements. Under the free-inspection procedure, the duration threshold for seeing the illusory triangle was about 9 ms while the t hreshold for discriminating the shape of the inducing elements was abo ut 2 ms. A static representation of the dynamic procedure used by Gell atly has been derived, which shows a novel effect of contour completio n across boundaries resulting in a ghostly white triangle.