Entertaining children during a long car trip is not an easy task. In these cases we usually make the situation more bearable by letting them read stories or use the tablet to play games or watch movies.
However, this relaxed moment can turn into an odyssey when one of the passengers turns pale and announces that his stomach is turning and he feels nauseated. And it is that keeping your eyes fixed on one point while the vehicle is moving can cause, in some people, an unpleasant sensation of dizziness. What triggers it? And why doesn't it usually happen to the driver or the passenger who occupy the front seats?
To understand the sensation of motion sickness, called motion sickness, we have to talk about the mechanisms of spatial orientation. That is, how we locate our position in the space that surrounds us to distinguish, for example, where it is up and where it is down. So we can maintain body posture, move and interact with our environment.
Three main systems participate in this task: the vestibular, the visual and the proprioceptive, of which we will now tell more details.
Maintaining body posture depends mainly on a sense that, despite its importance, is not included in the classic and incorrect list of five that we all know. It is about the sense of balance, mediated by the vestibular system. In addition to maintaining body posture and balance, it performs other very important functions, such as allowing us to fix our eyes on one point.
The sense of balance is located in our inner ear and consists of two components: the semicircular canals, which detect rotations; and otoliths, which capture linear accelerations, including gravity. In this way, the vestibular system empowers us to determine our position and know when we are moving.
However, it has its limitations. For example, if we move at a constant speed, then there is no acceleration and therefore the vestibular system does not detect such movement. This explains the sensation of remaining immobile while going up or down in an elevator.
On the other hand, if we are seeing everything moving around us, it is most likely that we are the ones who are moving. Therefore, to maintain body posture, vision also plays an important role. But the visual system is not infallible either, and sometimes the scene we are looking at moves even though we remain still.
An example is being stopped near a large vehicle, such as a bus, that suddenly moves, giving us the feeling that we are the ones moving. This occurs because the bus occupies a large part of what we are seeing.
Therefore, the vestibular and visual systems complement each other making our spatial orientation more precise, and there are other systems that also contribute. One of them is the proprioceptive system, which uses sensors in the muscles, tendons and joints to know the force and position generated by our own movements.
Using different strategies makes our spatial orientation work very well in most scenarios. However, during more recent history, human inventions have created new situations that challenge our spatial orientation.
Amusement parks, for example, are a space created in order to take this orientation to the extreme. Means of transportation also create an alteration of the conditions that shaped our ability to situate ourselves in space throughout evolution. And the car is no exception.
When we read or watch a movie in a moving vehicle, our visual system focuses on one point. While the proprioceptive system tells us that we are sitting motionless inside the vehicle, the vestibular system tells us that we are moving. That is, contradictory information reaches our brain through these three systems.
Likewise, there may be a conflict when we see objects passing through the window at high speed, since, when they are blurred, the brain is unable to interpret that information. This also helps make us dizzy.
As we get older, we can conquer the front seat, where we have a much wider field of vision and can see the distant horizon moving slowly through the windshield. This privileged place resolves the conflict between the visual and vestibular systems because the brain receives similar information on the direction and speed of movement through the ears and the eyes.
Another solution to this war between systems is to keep the head supported and as straight as possible so as not to further disrupt the vestibular system. Although, without a doubt, the best option is to stop the vehicle from time to time and take a short walk to restore the balance between the systems.
This article was originally published on The Conversation.
