<P> Reification is the constructive or generative aspect of perception, by which the experienced percept contains more explicit spatial information than the sensory stimulus on which it is based . </P> <P> For instance, a triangle is perceived in picture A, though no triangle is there . In pictures B and D the eye recognizes disparate shapes as "belonging" to a single shape, in C a complete three - dimensional shape is seen, where in actuality no such thing is drawn . </P> <P> Reification can be explained by progress in the study of illusory contours, which are treated by the visual system as "real" contours . </P> <P> Multistability (or multistable perception) is the tendency of ambiguous perceptual experiences to pop back and forth unstably between two or more alternative interpretations . This is seen, for example, in the Necker cube and Rubin's Figure / Vase illusion shown here . Other examples include the three - legged blivet and artist M.C. Escher's artwork and the appearance of flashing marquee lights moving first one direction and then suddenly the other . Again, gestalt does not explain how images appear multistable, only that they do . </P>

Who would not be considered a precursor to gestalt psychology