The brain is a fabulously powerful computer that uses factual information plus intelligent reasoning to work out things that we take for granted. Depth perception is a perfect example. How far away is that chair you’re looking at? We look at it with two eyes, and each one sees it slightly differently, from a different angle, because they are roughly 6cms apart and therefore do not see the chair in exactly the same way.
This is sometimes known as disparity. The brain takes both impressions and calculates the distance by combining the two. Our reasoning and experience can put a figure on it, but that is like the icing on the cake of the calculation; what we need to know most often is roughly how far away it is, to determine if we can reach out and touch it or if we are likely to bump into it.
When an object is close to us our eyes angle in on it and the brain uses information such as the effort the muscles use to calculate the distance. This is called convergence, and again our experience and knowledge of units of measurement can put an approximate figure on it.
Depth perception also enables us to see the shape of something. We can see how wide it is and how long in terms of distance from the front to the back. Our reasoning and experience will provide some approximate figures, but our eyes have done much of the work.
Does Depth Perception Rely on Having Two Eyes?
The separate reports supplied by the two eyes helps us with our calculations up to a distance of about 2m, but after that the differences are too small to be useful.
If we look with only one eye, the brain will still glean as much information as it can through such means as the effort the muscles use, as it does with convergence. It will also note how sharp an image is, because the closer it is to us, the clearer it will be, which enables us to compare two or more objects and know which ones are closer or further away.
The brain will notice the vividness of colours and the definition of textures, plus many more factors we would not consciously be thinking about. Closer means more vivid and detailed, and vice versa.
So, having two eyes helps us with depth perception up to a point, but it is not the only way we work this out.
Why is Depth Perception Important?
We rely on depth perception in countless ways all the time. It is what enables us to walk around without bumping into people or objects and it is obviously crucial in driving, knowing how close we are to the vehicle in front and how much clearance we have when overtaking or parking.
We use it all the time in sport, our brain giving us incredibly fast updates so a batter or fielder can keep track of the ball in cricket or baseball, a goalkeeper can make a save in soccer and a rugby player can time a tackle or evade an opponent.
The difference between us thinking about it and our body doing something about it is that the brain is on the case all the time, making calculations as a matter of course. We don’t have to turn on our depth perception monitor; it’s on permanently. To learn more about depth perception, visit Microprism Vision.