OFFICIALLY it鈥檚 to do with uncertainty or inexactness of meaning, or a lack of decisiveness or commitment resulting from a failure to make a choice between alternatives. Yes?
But there鈥檚 much more to ambiguity than that. New brain imaging studies shows that visual ambiguity, at least, may be the exact opposite: a state of too much certainty, where we have to distinguish between equally correct interpretations. By studying ambiguity, researchers may find how, in the face of equally good choices, our brains 鈥渄ecide鈥� what we are seeing. They may even catch a little glimpse of consciousness at work.
So what does visual ambiguity look like? A classic example is the Kanizsa cube (see picture)-an optical illusion in which a two-dimensional set of lines suggests a three-dimensional cube. The illusion is created because there are two ways to see the cube: either it seems to come out of the page with its closest side pointing down and to the left, or with its closest side pointing up and to the right.
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At first, you only see one position: stare at the cube long enough and it will suddenly flip to the other one. Keep staring, and it will switch back and forth.
What鈥檚 going on? Neuroscientists such as Semir Zeki of University College London and Andreas Kleinschmidt of Goethe University in Frankfurt am Main used functional MRI scans to probe our brains when we view these ambiguous, 鈥渂i-stable鈥� images. Zeki found that as the cube seems to switch position, different brain regions are activated, flashing back and forth between neural clusters.
鈥淰isual ambiguity may be a state of too much certainty鈥�
How does that help us? Ambiguous images such as the Kanizsa cube may be useful in that most difficult of tasks: finding out what the brain鈥檚 physiology is doing as it makes sense of the world 鈥渙ut there鈥� 鈥� and how well that sense fits with the 鈥渞eal鈥� world. This is a key problem in consciousness studies. Kanizsa images seem to avoid these problems because we know that while the brain perceives different images, the stimulus remains the same: we see the cube in one position or the other, but never both at once.
Isn鈥檛 that a bit quantum? Not really: it鈥檚 more like binocular rivalry, where each eye is presented with a different image at the same time, say of a house and a bike. Intriguingly, we don鈥檛 blend the two images but perceive alternating single images: house then bike, back and forth, because different clusters of neurons are fighting for attention, rather than working together.
These studies help confirm the notion of the brain as a 鈥渕eaning machine鈥�. If the brain faithfully represented the world as it is out there, we would see the Kanizsa cube as a bunch of lines on a page, and the house and bike as a strangely blended scene. Instead, we select information and construct interpretations. When no one interpretation is most likely, we alternate between possibilities.
How amazing that something so ambiguous could give us some clear insights?