Article:

Inversion und Ambiguität. Kapitel aus der psychologischen Optik

Optical inversion and ambiguity are not all the same thing. Within the relevant literature inversion seems to appear first. In 1613, in the fourth of his Opticorum Libri sex – illustrated by Rubens – Aguilonius mentions the nonveridical perception of concave hollows (for instance marks of cannon balls on a fortress’ walls) as convex bumps. If this view persists, as it is generally the case, inversion without ambiguity or forced inversion occurs. Inversion with ambiguity is, on the other hand, addressed by Robert Smith 1738, Porterfield 1759 or Sinsteden 1860, when they describe how the sails of a distant windmill allow an observer to recognize that their rotation-plane is tilted compared to the fronto-parallel one, but not their direction, so that it remains undecided, what is front, what is rear. Equivalence of front and back owing to parallel projection is equally the case in pictorial space; Necker 1832 observed »a sudden and involuntary change in the apparent position of a crystal or solid representend in an engraved figure« (Dember 1964: 78), and Schröder’s ›Staircase‹ (1858) was always a plane reversal figure. Soon after the French Revolution, about 1793, a picture puzzle was originated which enclosed the profiles of the recently executed royal couple; Rubin’s ›Goblet‹ with its rivalling contours could well have been modelled on this. Another class of reversal figures contains Jastrow’s ›Duck-Rabbit‹ and the ›Wife/Mother-in-Law‹-figure. Inversion with ambiguity brings about »that alternative perceptions can arise from the same optic array« (Gibson 1966: 246). This alternation of aspects has been on the minds of theorists from Wundt till Wittgenstein and has been used for the elucidation of views.