The Ghosts We Think We See

Bruce Hood usually conducts experiments under much more rigorous conditions than this, but since he had a large audience one recent evening in London, the University of Bristol psychology professor figured he'd seize the opportunity. Holding up an old cardigan, he asked if anyone would be willing to wear it if he paid them £20 (about $40). Every hand shot up. Then Hood added that the sweater had been worn by a notorious murderer. All but a couple of hands disappeared. "People view evil as something physical, even tangible, and able to infect the sweater" as easily as lice, Hood says. That idea helps explain a number of supernatural beliefs, he argues: "The idea of spirits and souls appearing in this world becomes more plausible if we believe in general that the nonphysical can transfer over to the physical world."

And believe it we do. A Gallup poll found that only 7 percent of Americans do not believe in telepathy, déjà vu, ghosts, past lives or other supernatural phenomena, which may have more than a little to do with the soaring popularity of Halloween. Even eminent rationalists such as Alfred Russel Wallace, who discovered natural selection (prompting Darwin to speed up his own work), believed in ghosts, haunted houses, levitation and clairvoyance. But "supernatural"—anything that cannot be explained by laws of physics or biology—also encompasses more mundane phenomena. It includes the belief that you can feel someone staring at you from behind, and that if you think about someone he is more likely to phone you (this doesn't work for getting first dates to call you for a second, however). Far from being pathological, the ubiquity of such beliefs is actually a clue to how the normal mind works, cognitive scientists now realize, for belief in the supernatural arises from the same mental processes that underlie everyday reasoning and perception.

Chief among those normal processes is our neurons' habit of filling in the blanks. The brain takes messy, incomplete input and turns it into a meaningful, complete picture. Visualize four Pac-Man-like black shapes arranged so that the wedge removed from each seems to form a corner of a white square. Neurons in the brain's visual regions, whose job is to fire when the eyes see a square's edges, do fire—even though there are no edges to see. The mind also sees patterns in random data, which is why the sky is speckled with bears and big dippers. This drive to perceive patterns—which is very useful in interpreting experimental data as well as understanding people's behavior—can also underlie such supernatural beliefs as seeing Jesus in the scorch marks and flecks of grain on a grilled-cheese sandwich. "If a stain looks like the Virgin Mary," says Hood, "then it is a divine sign and not a coincidence. If the wind in the cave sounds like a voice, then it is a voice."

Patterns can be in time as well as space. Hence such superstitious rituals as wearing the same shirt when you compete in a sports event, or not standing on the white lines of a tennis court, as John McEnroe refused to do. If you depart from the ritual to prove to a skeptic that it really works, you become so tense about the loss of the magic talisman that you're indeed likely to lose. Game, set and match for superstition.

The mind also tends to impute consciousness to inanimate objects (ever yell at a balky computer?). This leads us to believe that natural phenomena are "purposeful, caused by agents with sentient minds," says Hood, whose book "The Supernatural Sense" is due next year. It's only a short step to thinking that " 'things that go bump in the night' are the result of some spirit or agent," not branches brushing against your drainpipe.

The belief that minds are not bound to bodies reflects a dualism that shows up in children as young as 2. "This is universal, seeing minds as separate from bodies," says psychologist Paul Bloom of Yale University. "Kids have no trouble believing stories in which people exchange bodies, for instance. And since supernatural beings like ghosts are without material bodies but with minds, our belief in dualism makes them totally plausible."