Jonah Lehrer in Wired:
Here’s a brain teaser: Your task is to move a single line so that the false arithmetic statement below becomes true.
IV = III + III
Did you get it? In this case, the solution is rather obvious – you should move the first “I” to the right side of the “V,” so that the statement now reads: VI = III + III. Not surprisingly, the vast majority of people (92 percent) quickly solve this problem, as it requires a standard problem-solving approach in which only the answer is altered. What’s perhaps a bit more surprising is that nearly 90 percent of patients with brain damage to the prefrontal lobes — this leaves them with severe attentional deficits, unable to control their mental spotlight — are also able to find the answer.
Here’s a much more challenging equation to fix:
III = III + III
In this case, only 43 percent of normal subjects were able to solve the problem. Most stared at the Roman numerals for a few minutes and then surrendered. The patients who couldn’t pay attention, however, had an 82 percent success rate. What accounts for this bizarre result? Why does brain damage dramatically improve performance on a hard creative task? The explanation is rooted in the unexpected nature of the solution, which involves moving the vertical matchstick in the plus sign, transforming it into an equal sign. (The equation is now a simple tautology: III = III = III.) The reason this puzzle is so difficult, at least for people without brain damage, has to do with the standard constraints of math problems. Because we’re not used to thinking about the operator, most people quickly fix their attention on the roman numerals. But that’s a dead end. The patients with a severe cognitive deficit, in contrast, can’t restrict their search. They are forced by their brain injury to consider a much wider range of possible answers. And this is why they’re nearly twice as likely to have a breakthrough.