Illusions: Carried to Extremes; July / August 2010; Scientific American Mind; by Vilayanur S. Ramachandran & Diane Rogers-Ramachandran; 3 Page(s)

If someone showed you a caricature of Richard Nixon—a man’s face with oversize shaggy eyebrows, a bulbous nose and pronounced jowls—you would probably recognize the former president immediately, even though the drawing is not true to life. A cartoonist creates such a sketch by taking the average of many male faces and subtracting it from Nixon’s face, then amplifying those distinctive differences. To an observer, the result looks more like Nixon than Nixon himself. Why is it that our brains respond so intensely to extremes?

When the cartoon’s “Nixon-ness” jumps out at you, you are experiencing what scientists call “peak shift.” To understand the concept, imagine, for argument’s sake, that you want to teach a rat to distinguish a rectangle from a square. It’s quite easy to do. Simply give the animal cheese every time it picks the rectangle, and it will soon learn to select the rectangle every time. Once the rat has developed this preference, let’s say you show it a longer, skinnier rectangle. Inevitably, you will find that the rat prefers the exaggerated one to the original. What the rat has learned to recognize is not a particular rectangle but rather rectangularity itself: the more rectangular the better. The savvy rodent looks at the longer, skinnier quadrilateral and goes, “Wow, what a rectangle!” In scientific parlance, the rat’s “peak response”—its strongest reaction—has shifted away from the original—hence the term “peak shift.”