Sunday, July 31, 2005

On Haunted Houses

I have an older SUV that lacks much of the padding and upholstry buyers expect nowadays. My radio is also kaput, and driving home one day this spurred an interesting idea: everybody's familiar with that "hairs stand up on the back of your neck" feeling you get from time to time. It is strongly correlated with dark, creepy places and a history of horror movie fandom. But what makes a place creepy? Bloody handprints certainly help, but I'm talking about the subconscious lizard-brain feelings of unease we get walking around in abandoned houses and mental institutions - and I think I have at least a partial answer. It seems so obvious in retrospect that I assume I am not the first person to make this suggestion, though Googling yields nothing.

Feelings of creepiness are an evolutionary response to the auditory sensation of movement we can't see a cause for. Consider your average Sci-Fi channel Real Ghost Hunters special. Teams of "researchers" with thermal imaging equipment and audio gear load up and camp out in what is usually a dilapidated residence. Rarely do they visit, say, 80s-era corporate office buildings (ostensibly because fewer evil deeds of a magnitude to create hauntings take place there). Anyway, the thermal imaging equipment is brought along because feelings of a ghostly presence often coincide with unexplainable cold spots that can be electronically verified - giving some validation to people's very subjective feelings that they aren't alone. My thesis is that it is the cold spots that cause these feelings of unease, even if people can't feel the change in temperature.

In well-constructed buildings that are relatively small, and in the great out of doors, the air temperature tends to be homogeneous. Ambient noises in such surroundings - the sound of the wind in the trees or of one's own breathing - travel in predictable billiards-table paths and reflect at billiards-table angles. Not all environments are so homogeneous, however. Submariners and deep-sea fishermen are aware of the thermocline, a sharp boundary in sea temperature that sonically divides the sea less than, say, 150 feet deep, from that 175 feet and below. This temperature boundary layer is nearly opaque to acoustic signals. The temperature differences in "haunted" houses aren't nearly so sharp - but the density difference in the air is enough to lense sound away from its obvious source even though we can't see that anything has changed. Draftiness is a stereotype in stories about haunted buildings, and I think it is very likely a piece of unexamined folk wisdom.

So let's set this up, then. Let's say that in the mid-afternoon I assemble with my friends to tough out a night in a putatively haunted house. A few of us have analog watches, but all of us are breathing, so we have a foundation of small ambient noises that none of us consciously notices. As the sun sets and the air outside the house cools, air that was still in an uniform-temperature environment is now subject to mixing. Cooler air filters through cracks in the ceiling, just after night falls, and a column of cool air develops in the center of the room. The warm air/cool air boundary reflects some noises back to us much sooner (and therefore louder) than if they had travelled across the room unimpeded. Some sounds we are used to hearing, on a subconscious level, disappear as they are refracted or blocked by the air lens. In a homogeneous environment (such as we are evolved to) such a disturbance could have been created by a sneaking lion, say, or an approaching horde of attacking pygmies. If we turned a torch on either of those two, we could verify the causes of our unease. In this drafty house, however, the feeling is exacerbated by the fact that there is no visible cause for the change in the atmosphere. The evolutionary distress signals we are accustomed to follow have marooned us here, sensing movement (because the air is constantly shifting, and the apparent noise source shifts accordingly) where there is none. Freaky stuff.

The funny thing is that if these "haunted" houses were occupied, background noise from televisions, conversations, and the washing machine would probably be sufficient to drown out the lens effect. It is when one is relatively quiet (but not absolutely quiet, in which case there would be no noise to refract) that the lens effect becomes apparent.

There are two experiments that could verify this: send two teams of volunteers into a building reputed to be haunted, and record their pulse and breathing rates as they spend the night. One team gets noise-cancelling headphones, the other doesn't. I'd bet a considerable amount that those with the headphones would have a cakewalk (deaf volunteers would work even better, potentially).

The other is one you can do yourself. The next time you have some spare time, and a willing volunteer, blindfold yourself and have someone quietly light a candle at some distance behind you. Ask the person to snuff out the candle at his convenience but without telling you when. You'll be amazed to see how you can "hear" a burning candle in a quiet room, and tell when it's extinguished.

Which brings me to the question: do we become less afraid of ghosts and monsters as we grow older because we learn better, or because we hear worse?


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