An early ambiguous figure, first published by the Polish-born US psychologist Joseph Jastrow (1863–1944) in his book Fact and Fable in Psychology (1900), and later discussed by the Austrian-born British philosopher Ludwig (Josef Johann) Wittgenstein (1889–1951) in his Philosophical Investigations (1953, II.xi, pp. 194–206). The figure can be seen as a duck or a rabbit (see illustration), and Wittgenstein argued that recognition of what the figure represents comes only at the moment of change from one to the other and is not characteristic of the perception in general: ‘It would have made as little sense for me to say “Now I am seeing it as …” as to say at the sight of a knife and fork “Now I am seeing this as a knife and fork”. This expression would not be understood.’ (p. 195)
Duck-rabbit. A much-discussed reversible figure that appears as a duck facing left or a rabbit facing right.