Late influences on perceptual grouping: Illusory figures

Two experiments demonstrate that grouping can be strongly influenced by the presence of figures defined by illusory contours. Rectangular arrays were constructed in which a central column of figures could group either with th ose on one side, on the basis of perception of figures defined by illusory contours, or with those on the other side, on the basis of physically prese nt inducing elements. In all displays, subjects grouped according to the il lusory figures significantly more often than for control displays that cont ained the same inducing elements, but rearranged so that illusory contours were degraded or eliminated. A second experiment showed that in objectively defined grouping tasks, subjects grouped faster by illusory figures than b y inducing elements. These results indicate that grouping can occur after i llusory contours have been perceived.