The Blair Witch Project is a psychological horror film about a group of students lost in the woods. When it was released in 1999, it made audiences sick to the stomach—and not just because of sheer terror. The shaky, hand-held camera view led some people to feel dizzy, sweaty and nauseous. These are all symptoms of kinetosis, or motion sickness.
When you think of things that can cause motion sickness, movies probably aren’t at the top of the list. Cars, boats and amusement park rides might be more familiar examples. But motion sickness can also strike when you’re relatively still. For example, you might get sick when you play a first-person shooter game or watch a movie with shaky images.
But why does motion sickness happen? Most scientists would point to the sensory mismatch theory. Essentially, you get sick because what you see doesn’t match what you feel. So to understand motion sickness, you need to understand how your body senses motion.
Seeing and feeling motion
Two systems in your body help you process motion. The visual system lets you to see movement. It consists of your eyes, the associated brain areas and the nerves that connect the two. The vestibular system helps you feel movement. It consists of tiny organs within your inner ear, the associated brain areas and the nerves that connect the two.
When you see a moving car, that’s your visual system at work. When you’re inside a car and feel it moving, that’s your vestibular system at work. It’s the reason you can still feel the car moving even when your eyes are closed.
Did you know? The English word “nausea” comes from a Greek word that means seasickness.
The Sensory Mismatch Theory
There are several theories about why motion sickness happens. But the most widely accepted is the sensory mismatch theory. According to this theory, motion sickness happens because the information you’re getting from your visual system conflicts with what you’re getting from your vestibular system. In other words, what you see, what you feel and what you think is going on don’t match up.
Here are some ways that this information can end up mismatched:
- Motion you feel but don’t see
Do you or someone you know get sick when reading in a car?That’s because your vestibular system detects movement, but your visual system does not. In other words, the car is moving, but the book is not. Seasickness and airsickness also fall into this category. Your vestibular system senses that the boat or airplane is moving, but your visual system sees still water or sky.
- Motion you see but don’t feel
The stomach-sick viewers of The Blair Witch Project fall into this category. So do people who get sick while playing video games. In both of these cases, you can see movement. But because you’re just sitting down, your vestibular system does not detect movement.
- Motion you see that doesn’t match with the motion you feel
Let’s say you were on an amusement park ride wearing a virtual reality headset. Imagine that you see a spaceship moving straight, but the ride itself is moving in circles. In this case, you see straight motion but you feel circular motion. Because these don’t match, this ride might make you nauseous.
The Toxin Detector Hypothesis
Why would this conflicting information make you sick? One possible explanation is the toxin detector hypothesis. According to this theory, your brain thinks a sensory mismatch means your body has ingested a neurotoxin, and it makes you vomit to get rid of the poison.
Did you know? Fish can experience seasickness, too! It can happen when you move them from one aquarium to another.
Many factors can contribute to how likely you are to get motion sickness. For example, women are more likely to experience motion sickness than men.
Age is an important factor, too. Generally, children below the age of seven do not experience motion sickness. This could be because the brain areas involved in motion processing haven’t fully matured yet. In your teens and early 20s, your susceptibility to motion sickness decreases again. This is likely because, over time, you get used to many different types of motion. So don’t worry if you get sick during boat rides or plane rides. It’s possible that the more you experience these rides, the less motion sickness you’ll experience in the future!
Preventing motion sickness
You now have some possible explanations for how and why motion sickness happens. There’s also plenty of ongoing research into the causes of motion sickness, and how you can treat or even prevent it. In the meantime, if you get motion sick, medication might help. You can also try behavioural strategies. For example, try focusing on a fixed point far in the distance when you’re in a boat, plane or car. Happy travels!