Can you trust your eyesight? When your eyes take in that information for your brain to process, bear in mind that what you notice is only a small bit of what you see, and that’s all you’re left with to process. Then it gets weird – what if through the way you are, the way your brain is wired, what you see is not the same as what someone else sees, and the only difference really is because you two are different people. I’m not just talking about two different people’s sense of aesthetics, I’m actually talking about how they perceive things in three-dimensional space. What we see, and what we perceive, is the real world with a lot of post-processing created by your own mind. Thus, you don’t see what you see, you see what your brain sees. So, can you trust your eyesight?
Now that I’m done messing with you (I’m not evil, but I do swing Chaotic Neutral), I did all of that because of an article published recently in Science Advances. According to the authors, we all have an “intrinsic spatial knowledge” that we use to create the three-dimensional space that we perceive. The authors propose that there is an imaginary curved surface between your eye level and your feet that, in the absence of a lot of visual information, you place an object when you’re not sure how far from you it really is. They call it an “intrinsic bias.” But just how does this bias come about?
The authors hypothesize that it’s derived from our experiences with a dealing with things on the ground – we guess an object’s distance relative to where we think the ground is. The same can’t be said for things on the ceiling, which makes sense since the ground is pretty much where we think it is, but the ceiling will always vary. We’re also more likely to find things on the ground, orient our body shape relative to the ground, even make friends with it. So, the intrinsic bias is probably going to be flatter relative to the ceiling. In addition, height is going to play a factor; remember, the intrinsic bias curve starts at the eye level and ends at the feet. Taller people, then, should have a very different curve than shorter people. So, does this bias really play out this way? Zhou et al. find out by having tall and short subjects (males and females at each type of height) try to find things in the dark, in a ‘reduced cue’ environment (think dark room but it looks like it’s dotted with starlight, how romantic), and an environment with all visual cues. In the last one, the lights are on, so the subjects know where everything is, particularly the floor. The subjects should be better judges of distance in this experiment. However, now they have to judge the distances of two objects on the floor in increasing distances.
So what did they learn? First, the asymmetry does exist – the intrinsic bias curve above the eye level is somewhat flatter than below the eye (the one that curves to your feet). However, taller people seem to have a less-flatter upper curve than shorter subjects. I wonder if it’s because people keep asking us to grab really high things – anyway. The second and third experiments found something rather interesting (and this is the finding that’s been making the rounds in science news last month) – taller people seem to be better at judging distance at medium distances, even when they were sitting on chairs (shorter subjects stood on boxes).
The intrinsic bias is more likely to come up when there’s less visual information to help you, and it isn’t just limited to the dark, if you think about it. Try to find someone in a crowd, sure, you would look for their face, but you’re not sure where exactly they are relative to you. You don’t have the ground to help you judge distance, so you’ll have to use other things. You may have to use some markers, like maybe two rows up, or next to that pretty girl, and so on.
That is, of course, if you choose to trust your own eyes, which may not even be your own. It may be your brain’s eyes after all…
Featured Article: Zhou L, Ooi TL, He ZJ. (2016) Intrinsic spatial knowledge about terrestrial ecology favors the tall for judging distance. Sci. Adv. doi: 10.1126/sciadv.150170.
Featured Image credit: Wikimedia Commons, CC-BY-30 Netherlands (author: Harry Pot; Nationaal Archief Fotocolletie Anefo)