Ambiguity of form: Old and new

The two-fold appearances of certain two-dimensional spatial patterns are described. While these ambiguous figures have been employed extensively in a variety of experimental studies of perceptual organization, their use extends beyond psychology and reaches back into antiquity. Regrettably, very few examples of such patterns remain available. A more-or-less comprehensive set of well-known ambiguous figures is described and illustrated, including an equi-ambiguous version of the “chalice and faces”. An attempt is made to devise new examples of such figures adding to the repertoire of materials available for studying relevant aspects of visual perception.