THE BRAIN abhors ambiguity, yet we are curiously attracted to it. Many famous visual illusions exploit ambiguity to titillate the senses. Resolving uncertainties creates a pleasant jolt in your brain, similar to the one you experience in the “Eureka!” moment of solving a problem. Such observations led German physicist, psychologist and ophthalmologist Hermann von Helmholtz to point out that perception has a good deal in common with intellectual problem solving. More recently, the idea has been revived and championed eloquently by neuropsychologist Richard L. Gregory of the University of Bristol in England.