Humans have some of the most sensitive eyes on the planet. We have a type of vision classified as trichromatic. This essentially means that our eyes have three different types of color receptors known as cone cells. These cone cells are attuned to blue, green and red. All the beauty of the world comes to us through a mix of signals from these three types of cells. In total we’re able to see up to 10 million different colors through activation of different patterns of our cone cells.
In contrast, most of our fellow mammals are dichromats. This means that almost any warm blooded animal we see is probably only able to view the world in a very limited color palette. They typically see the world in something akin to an old sepia photograph or a black and white image. This isn’t a perfect analogy of course. The full range of mammalian life encompasses a wide variety of different eyes. But as a general rule it’s safe to say that humans occupy a rare and colorful position among mammals.
But what about the other side of the comparison? If we see the world in a more colorful way than most mammals, are there any animals which see better than we can? In fact there are a number of animals which see more colors than humans. Birds, for example, have all the color receptors we do. But on top of this our feathered friends are also able to see into the ultraviolet color range.
However, there’s one particular animal people typically hold up when this question arises. The mantis shrimp has achieved a reputation for some powerful eyes. Most people who are aware of mantis shrimp will argue that the crustaceans can see far more colors than humans. But is that really true?
The Main Evidence for the Mantis Shrimp’s Sense of Color
The main reason why people argue that mantis shrimp can see more colors than humans is due to their number of photoreceptors. Humans have three types of color activated photoreceptors. Some species, such as birds, have four. This gives these animals the ability to see colors which are invisible to us such as ultraviolet. However, mantis shrimp have an incredible twelve to sixteen different types of photoreceptors.
This fact led people to assume that a mantis can see far more colors than humans. After all, it makes sense that sixteen different types of photoreceptors could outperform three. This assumption also brings up an important fact about science. We always need to remember to test our assumptions. In this case it may well be that we’re assuming too much when we take visual processing for granted. In short, is the mantis shrimp using its photoreceptors in the same way that we use ours?
Some Highly Educated Crustaceans Help Us Find Concrete Answers
Researchers decided to put the mantis shrimp’s color vision to the test. The scientists carefully trained mantis shrimp to respond to one of ten specific color wavelengths. The shrimp were presented with treats for choosing the right color. These trained mantis shrimp were then faced with a challenge.
The mantis shrimp needed to differentiate the feeding color they’d been trained on from a similar one. The shrimp had significant issues telling the difference between similar colors. This suggests that their ability to differentiate between colors might actually be worse than humans. But how does this make sense given the mantis shrimp’s large number of photoreceptors? The answer can be found by taking a deeper look into both the human and shrimp’s nervous system.
Different Needs and Different Approaches to Color Recognition
What actually happens when we see complex colors? Imagine walking through a park on a brisk autumn day. You look around and see a yellow leaf falling to the ground. Your attention is probably first attracted by the leaf’s motion. You probably won’t give any conscious thought to the motion which first caught your gaze.
As the leaf falls your eye’s photoreceptors will process its reflected light. Your blue photoreceptors wouldn’t show much activity. However, your green and red cone cells would send activity along to your brain. Of course each of your eyes is performing this function at the same time to produce two different data sets. All of this data would converge and present the view of a yellow leaf to your conscious mind. That’s a lot of work just to register a color isn’t it?
Researchers now believe that the mantis shrimp has found a shortcut to color processing. The shrimp’s large number of photoreceptors can simply pick up complex colors without any need to merge multiple sources of information. Humans need to think about colors before seeing them. To be sure, this is all done unconsciously. But that processing means that our consciousness is just a little behind what’s actually occurring in the real world. Humans don’t really see the present.
Our view of the world is always slightly behind the reality due to the fact that it takes a while for our brains to process all the information coming in from our eyes. This doesn’t matter much to us because we live in a world shaped by similar slow processes. However, that isn’t true for the mantis shrimp.
A Different Type of Vision for a Different Pace in Life
A mantis shrimp can move at an incredibly fast pace. In fact, the little creatures are able to punch at 50 mph. Their blows are so powerful that they can break through an aquarium. It’s estimated that the force created by such huge speeds is equal to a 22-caliber bullet.
Saying that a mantis shrimp values speed is a tremendous understatement. This is where their very different type of color vision comes into play. Remember how much work a human has to put into seeing a complex color. The shrimp bypasses all of this neurological legwork. Instead of combining base colors together to see a more complex color the shrimp simply sees the complex color. This can help a mantis shrimp see and catch his prey faster. Likewise, it also means that he can react to the prey faster than competing predators.
This seems to suggest that a shrimp’s supervision is something of a myth. But we need to remember that there’s more to vision than color combinations. And the shrimp’s eyes still have some amazing surprises for us.
A Unique Way of Interacting With Ultraviolet Light
We’ve known from the start that the mantis shrimp could see ultraviolet light better than humans. Not that this is a particularly difficult feat given that humans are blind to light in the ultraviolet range. However, it turns out that the mantis shrimp takes ultraviolet sensitivity into some strange directions.
Mantis shrimp use a pigment called opsin to help recognize color. Most animals have a direct one-to-one relation between a photoreceptor and opsin. But mantis shrimp have six photoreceptors which detect light in the ultraviolet range. However they only have two opsins sensitive to ultraviolet light. Nature tends to abhor biological wastefulness. And a shrimp certainly isn’t going to waste precious calories maintaining superfluous visual receptors. So why does it seem like the mantis shrimp has more ultraviolet receptors than it’s able to properly use?
The answer is found in a crystalline structure above each ultraviolet photoreceptor. These structures contain mycosporine-like amino acids. These amino acids, also known as MAAs, can block or filter UV light. In effect ultraviolet light is physically sorted by the MAAs without ever needing any biological processing. We can guess that this too all works to increase the mantis shrimp’s ability to react to color as quickly as possible.
A Polarized View of the World
The mantis shrimp has another visual quirk which we need to consider. Like many other undersea animals a mantis shrimp can see polarized light. By this point it shouldn’t come as much of a surprise to find that the mantis shrimp goes about this process differently than other animals.
Animals sensitive to polarized light usually only recognize it in a linearly polarized pattern. And the mantis shrimp can indeed see linearly polarized light. However, it’s also capable of seeing circularly polarized light.
Of course this raises a question about why the mantis shrimp is able to see both types of polarized light in the first place. Nobody is quite certain what role circularly polarized light plays in a mantis shrimp’s life. But some researchers suspect that it has something to do with their abnormally social nature.
Crustaceans as a whole aren’t very social animals. But the mantis shrimp is a notable exception to this rule. As we’ve seen, these little creatures tend to be contrarian in almost every aspect of their life. And this is true for the mantis shrimp’s mating practices as well.
Many types of mantis shrimp are monogamous. When a mantis shrimp finds that special partner they’ll stay together for multiple mating cycles. What’s more, many species of mantis shrimp even take care of their eggs together. You might wonder what this has to do with circularly polarized light.
It turns out that the mantis shrimp itself can emit reflected circularly polarized light. It’s thought that this type of light might act as a signal to other mantis shrimp. Basically it can be thought of as a special name tag that only other mantis shrimp are aware of. In that way they’re able to covertly communicate without attracting too much attention. This could be an ideal relationship for small animals which don’t necessarily want to announce their presence to the world. Especially if the small animals have teamed up to protect their very vulnerable offspring. Likewise it could help mantis shrimp differentiate between their mated partner and other members of their species.
Bringing It All Together to Form a Solid Answer
So far we’ve seen one fact about mantis shrimp come up again and again. The mantis shrimp’s vision is, in short, strange. Their eyes are so strange that it’s difficult to make strict comparisons to other animals. Asking if a mantis shrimp sees more colors than humans is somewhat akin to asking whether apples are better than oranges.
A mantis shrimp’s vision isn’t just about their photoreceptors. We also need to consider how those photoreceptors work when compared to that of a mammal. Likewise, there’s also the important issue of neurological differences in a mantis shrimp and a human. The human brain handles a lot of our color perception. Meanwhile it appears that the mantis shrimp’s biology is framed around a principle of avoiding as much neurological processing of visual data as possible.
It’s hard to say whether a mantis shrimp really sees more colors than humans. We can say for a fact that they see into ranges which humans can’t. But the mantis shrimp’s ability to make use of that data seems considerably lacking when compared to humans. On a technical level the data currently suggests that mantis shrimp have a larger range of color vision than humans but less ability to see variations within the color spectrum.
In the end it’s probably better to sidestep the question of whether a mantis shrimp sees more colors than humans. Instead, we should focus on the fact that mantis shrimp see the world in a remarkably complex and different way to humans. The mantis shrimp’s view of the world is so dissimilar that one-to-one comparisons with a human’s eyesight might not really be possible.
The mantis shrimp’s view of color is wonderfully alien to that of humans. Really, it’s distinct from the vision of most other forms of life on earth. Science is only just now starting to get a good idea of how the mantis shrimp sees things. But it’s clear that every new discovery will teach us just a little more about the nature of color perception.