Today I am going to tell you that you have rocks in your head. But don’t freak out; they are fairly harmless rocks. And in fact, throughout the course of your day, they are useful to you in all sorts of ways. You know when you’re tipping back in your office chair and you can sense that you’re just about to tip a little too far? Well you can thank these rocks in your head for allowing you to re-calibrate and preventing your fall!
They’re called otloliths (Greek for ear stones) and they’re crucial for helping us to maintain a sense of balance. As the etymology would suggest, they’re located in our inner ear (home to our vestibular system) along with a bunch of other stuff that is in there to help us walk, run, score touchdowns, etc. without ever falling over. They respond to both linear acceleration (so moving up or down) and the passive tilting of our heads (for example, when you look up at a skyscraper).
How they work is pretty basic: they’re fixed in a gelatinous material in your ear and surrounded by little tiny hair cells that send messages to your brain – either about your up/downward acceleration or your head tilting. So when you’re in an elevator or looking up at the sky, gravity acts on these rocks and essentially pulls them backwards, exerting pressure on those hair cells and starting a chain of reactions that tells your brain that you’re moving up or that you’re falling back.
Though otoliths are ultimately a key for helping us to stay up on our feet, they can be quite the little tricksters at times, and in some cases, they can even work against our best interest. Case in point: if you’re a pilot.
So imagine you’re a pilot. You’re just taking off from a runway. As the plane first leaves the ground, your otoliths start responding to the linear acceleration. They thus send you a signal of, “hey, you’re moving upwards.” But remember – they also respond to passive tilt. So during this takeoff, as your head naturally tilts backwards, the otolith rocks transduce even more signals from gravity – and what you get is essentially a “double whammy” of sensory information at once, both from leaning backwards and moving upwards. The result is an overrepresented, illusory effect on your perception, particularly about the angle at which the plane is flying (as a result, you end up overestimating the angle).
For pilots, without an awareness of this phenomenon, this illusion can mean life-or-death, and in the past, it often did. Back in the day, many planes were crashing at nighttime because of this “takeoff problem”; pilot trainees, relying on their perceptions alone as a guide for steering the plane, were unable to reconcile what their brain was telling them (i.e., the overestimated angle) from what – in reality – was the actual angle of the plane. The upshot of these early plane crashes, of course, was that during those initial moments of takeoff, pilots had to learn NOT to rely on their intuitive human senses, but rather to put stock in objective measures, such as gauges and -odometers, instead. Luckily for us today, all modern pilots are trained to use such measures.
You may be thinking, why would this happen at all? Our perceptual systems, after all, seem to do a pretty good job of getting us through our days in a relatively safe manner. So why in this takeoff scenario would our perception tell us one thing, but then the odometers tell us another? Well, it’s simple. Through evolution by natural selection, people have come to adopt some incredible capacities, perceptual ones included. Flying a plane, however, is not such a capacity. After all, planes were invented in 1903. That is relatively recent in the ~200,000 some years we have existed as a species. Had there been many analogous scenarios to this “takeoff problem” in the ancestral living space, perhaps we would have developed a mechanism to correct for it. But the fact that this illusion is still built into the perceptual systems of modern-day humans lays testament to the claim that – back in the day – these scenarios must have been relatively uncommon. Natural selection is not perfect. The way that it works is that the organisms which survive are the ones that adapt to the most pressing environmental constraints of the time. The “takeoff problem” was never such a constraint. Thus, developing a corrective mechanism for it would not have conferred enough of an advantage so as to override any of the existing perceptual hardware. So in 2015 we still have the same otoliths that we’ve always had; one’s that are imperfect for sure, but which were good enough at the time (and still pretty much are).
In sum, yes you have rocks in your head, but in most cases, they are there to offer you balance. More importantly, the story of otoliths in pilots is meant to drive home the point that we can not always put faith in our senses. If possible, it is usually wiser to consult facts and to employ some objective measures when we are making decisions.
So there’s my tidbit of sensation and perception for the day. Pretty neat stuff if you ask me!