Illusory contours and spatial judgment

We investigated whether, in the human visual system, the mechanisms respons ible for relative location judgments are the same when those judgments are made in the context of illusory contours and in the context of mentally joi ning two points. We asked subjects to align a dot with the oblique contour of an illusory surface or to align a dot with two markers at an oblique ori entation. The systematic errors differed in direction for these two conditi ons. All the systematic errors were orientation dependent. The errors in al igning a dot with an illusory contour seem to be related to the asymmetrica l shape of the single objects, which are able to induce an illusory contour , as well as figure-ground segregation.