Image:Duck-Rabbit illusion.jpg

The famous duck-rabbit ambiguous image. Is it a duck? Is it a rabbit?

"The subject of a gestalt demonstration knows that his perception has shifted because he can make it shift back and forth repeatedly while he holds the same book or piece of paper in his hands. Aware that nothing in his environment has changed, he directs his attention increasingly not to the figure (duck or rabbit) but to the lines of the paper he is looking at. Ultimate he may even learn to see those lines without seeing either of the figures, and he may then say (what he could not legitimately have said earlier) that it is these lines that he really sees but that he sees them alternately as a duck and as a rabbit. ...As in all similar psychological experiments, the effectiveness of the demonstration depends upon its being analyzable in this way. Unless there were an external standard with respect to which a switch of vision could be demonstrated, no conclusion about alternate perceptual possibilities could be drawn." -- Thomas Kuhn, The Structure of Scientific Revolutions (3rd edn., p. 114).

[edit] License

• Source: Jastrow, J. (1899). The mind's eye. Popular Science Monthly, 54, 299-312.

	This image is in the public domain in the United States. In most cases, this means that it was published in the United States prior to January 1, 1923 or that its first publication anywhere in the world was prior to January 1, 1909 or that its copyright expired in the United States.
	This image might not be in the public domain outside of the United States (this especially applies in Canada, China except Macao, Germany or Switzerland). The creator and year of publication are essential information and must be provided. See Wikipedia:Public domain and Wikipedia:Copyrights for more details.