(Intro)

It was a dark and stormy night and the SciShow team was working late into the night on the newest episode.  As they toiled late into the evening, they started to notice peculiar things.  There were sounds.  Was it a voice?  And the shadows, flitting just out of view.  It was then that they finally came face to face with the legendary ghost of SciShow.  Muaahahah!  

Now, I'm just kidding, but who doesn't love a good ghost story?  If you talk to the caretakers of old buildings or hop onto any number of subreddits, you're sure to find countless stories of personal run-ins with a spook, and encountering a ghost, whether it's in an old building, your bedroom, or in the SciShow office, does sound truly terrifying, so perhaps you can take comfort in the fact that these encounters can be explained by natural phenomena, no super prefix necessary, and a lot of it actually has to do with our brains and how they interpret the world around us.

If we want to talk about explanations for seeing ghosts, we should start by talking about our eyes.  Pretty much every ghost story happens at night or in a dark place, and that's probably not a coincidence.  Many ghost sightings are brief glimpses of something, just at the edge of a person's field of vision.  Then, they look to see what it was, but it's gone, and that kind of sighting can probably be chalked up to the way human peripheral vision works. 

You see, your ability to detect color and resolve detail drops off considerably at the edge of your visual field, but your ability to detect motion actually increases.  That's because the periphery of your retina has fewer cones, the light-sensing cells that excel at detecting color and shape, and more rods, which are better at detecting motion.  So especially in low light and/or high spook conditions, it's easy to notice motion out of the corner of your eye without clearly making out what's actually moving.

Plus, all of your senses can be heightened when you're on alert, which increases the likelihood you'll be frightened by otherwise mundane visible stimuli.  So if you just catch something moving out of the corner of your eye only to find nothing unusual there when you look, it probably wasn't a supernatural being.

It's much more likely that the mechanics of your eyeballs made something ordinary seem extraordinary than it is that a ghost crept past and then vanished.

One of the most common devices in a paranormal investigator's toolkit is the humble audio recorder.  They use it to pick up EVPs or Electronic Voice Phenomenons, it doesn't pluralize quite right when you spell it out.  Anyhow, the idea is that you can hit record, ask questions to a room, and then hear vocal responses in the audio when you play it back, and that's totally true.  It's just that those vocal responses aren't generated by ghosts.  They're generated by your brain.

Another way our brains can trick us is pareidolia, our tendency to find familiar patterns even where none exist.  We've talked about this before in the context of seeing faces in rocks or toast.  That happens because our primate brains evolved to quickly recognize one another, and that ability comes with a side effect of also recognizing familiar forms in otherwise random patterns.  Turns out, this isn't just a visual thing.  We're so keen on recognizing other humans that we often hear human voices that aren't really there.

This is what's known as audio pareidolia and it explains why you might hear a cryptic voice in radio static or someone whispering your name in the wind.  Basically, when your brain attempts to make sense from nonsense, static and amplified background noise are shaped into vague words.  Add a little sprinkling of wishful thinking because you're trying to hear words from the other side and you end up with a full blown ghost voicemail, and the power of suggestion can even alter what message you hear.

As we explained when we talked about auditory illusions, there are a lot of factors that can affect how your brain interprets ambiguous sounds.  Experiments from both white noise and human speech have demonstrated that if subjects are given context beforehand, their interpretation of a recording tends to match their preconceived expectations, even if the provided context is deliberately incorrect.  So if we were to play you something we recorded in the old sawmill across town at 3AM the other night, your impression would be very different if we told you that it said 'Get out' than if we told you the message was 'Eight cows'.  

Still, in either case, the recording in question wasn't actually speech or words at all.  It was just ambient noise.  So now you may be saying, nice try, SciShow, but you're not gonna convince me that ghosts are just when people get confused about motion off to the side or mishear static, and fair enough.  So let's crank up the science.

Another device no serious paranormal investigator would be caught dead without is an EMF detector.  EMF, of course, stands for electromagnetic field, the area of radiation that surrounds flowing electrical currents.  These fields can be naturally occurring or can come from electronics and they range in frequency.  

Now, paranormal investigators will tell you that EMF detectors track ghosts because their incorporeal forms generate EMFs, but some scientists think what's really going on is the opposite: EMFs may actually cause the feeling of being haunted.  We mentioned a while back that some ghost stories can be explained by the phenomenon of infrasound.  Those are sound waves with frequencies below the normal human range of hearing and though you can't hear them, they still make things in your body wiggle around a bit like other sound waves do, leading to everything from the feeling of being watched to outright seeing apparitions, and EMFs might be kind of similar, but instead of vibrating our bodies, they mess with our neurons.

Laboratory studies have demonstrated that low frequency EMFs can darken out mood or cause other negative psychological effects when applied to regions of the brain, and the effects can be much stronger, including visual hallucinations.  The catch is that not everyone may be affected the same way, if at all.  For example, the relatively minute EMF of an alarm clock was enough to make one patient hallucinate nighttime visitors in her bedroom, but it turned out that the magnetic pulses generated by the clock were similar to ones that can induce seizures in some people, and in this case, there was a specific interaction between the clock's EMFs and the patient's existing brain injury.

Because these fields can have such strong psychological effects, some scientists think the ubiquitous EMFs of the modern era are responsible for a lot of, if not most, ghostly experiences, but while the alarm clock was a slam dunk, definitively tracking down EMF sources in every haunting isn't so straightforward.

EMFs can come from oodles of sources, including just about every electronic device out there, so with all the WiFi and smartphones and such these days, it's nearly impossible to accurately isolate and assess the effects of specific electromagnetic signals.  Still, if a paranormal investigator tries to tell you than an EMF spike means that there's a ghost in the room with you, you can tell them that your BS detector is also spiking.

Some of the creepiest supposed encounters with ghosts are those that don't occur in some creepy haunted place.  They happen right in your bedroom.  Midnight visitations by shadowy figures are a major feature of personal ghost encounters and probably the freakiest of all, but your brain is probably to blame here, too, and a weird phenomenon called sleep paralysis.  In short, your body is asleep, but your brain isn't quite, and you get left experiencing an honest-to-goodness waking nightmare.  

Sleep paralysis tends to happen when the normal brain processes tied to sleep are accidentally disrupted, often due to some sort of chronic mental stress.  Neither your body nor your brain are fully awake, so you're somewhat aware of your surroundings but still unable to move and this is the key bit, still possibly dreaming, which is why people experiencing sleep paralysis often hallucinate.

Science isn't entirely sure why you see a ghostly form instead of other things, but it may have to do with how sleep-related brain processes go haywire.  In the lab, if you tamper with a part of the brain called the temporoparietal junction, you can give people out-of-body experiences because it's a key part of how we sense and recognize our own body.  It's normally not active when you're asleep, but it could be activated or partially activated during sleep paralysis, and that might mess with it just enough for you to sense your body as someone else.

You might even be convinced that the other person is somewhere else in the room.  Some psychologists have suggested that just the right neurons firing at just the wrong time may cause us to use the built-in blueprints of our bodies to hallucinate another being, and once that happens, mirror neurons could play a role in bringing that imagined other person to life.

These are neurons that fire in response to actions we see performed by others and importantly, which fire in the same way when we perform those actions ourselves.  If, during sleep paralysis, these neurons are firing while other weird neurological effects are happening, you could potentially misinterpret a self-made projection of another person, which is doing stuff your mind is making up as an autonomous entity controlling its own actions.  

In other words, your natural sleep cycle gets interrupted, your bleary brain makes you see a person, and then it tricks you into thinking that person is moving around right before your eyes.  Meanwhile, all you can do is look on helplessly frozen in place.  It might be terrifying, but it's nothing more than a sophisticated bad dream.  None of this is to say that anyone's haunting experience is any less valid or panic-inducing, just not that every one of these experiences should lead us to conclude that the answer is ghosts.

Ultimately, there's plenty out there that we don't understand and yes, that can be frightening, but in many cases, our lack of understanding is only because we haven't found the solution yet, not because things are too horrific or too unknowable to every make sense to us.  The world and your brain has a lot of weird stuff it can throw at you, but understanding it can make it less scary and science will always be there for you to make the paranormal just normal.

Thanks for watching this episode of SciShow.  If you like learning about the weirdness of your brain, you'll probably love our sister channel, SciShow Psych.  There, we dive into all sorts of questions about how human brains work and why they do strange things like make you see beings that aren't really there.  Just head over to youtube.com/scishowpsych to check it out.

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