The Duck Test


Today’s blog posts have been all about perception. The eye transmits images to the brain upside down and it is the brain which turns the images up the right way to make sense of what it sees: the eye and the brain have to work together to make sense of reality. But it doesn’t take much to deceive the eye, as anyone who has been taken in by a conjuror knows only too well.

You know about the duck test, don’t you? The American ambassador to Guatemala in 1950 accused the Guzmán government of being Communist. He had no proof, but explained:

Suppose you see a bird walking around in a farm yard. This bird has no label that says ‘duck’. But the bird certainly looks like a duck. Also, he goes to the pond and you notice that he swims like a duck. Then he opens his beak and quacks like a duck. Well, by this time you have probably reached the conclusion that the bird is a duck, whether he’s wearing a label or not.

Most of us routinely operate the duck test in making sense of reality.

The illustration is the famous ambiguous duck-rabbit 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. Ultimately 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).
Illustration via Wikimedia

About layanglicana

Author of books on Calcutta, Delhi and Dar es Salaam, I am now blogging as a lay person about the Church of England and the Anglican Communion. I am also blogging about the effects of World War One on the village of St Mary Bourne, Hampshire.
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