Do Animals Think With Their Eyes?

That disproportionally big, mushy thing up there in our heads – we normally assume it to be the sole seat of reason, the stuff that makes us capable of complex thought and intelligent behavior. Cognition, most people believe, is bound to the brain.

But might it be possible that what we normally call “cognition” does not happen exclusively in brains, but also in sense organs like the eyes? Before you exclaim that philosophers are getting crazier by the day, let me try to put things in a different light.

A snake with a thought bubble, saying 'i see, therefore i think'

Many people today, including scientists, believe something along the lines of “big brain equals high intelligence, and vice versa”. All that demanding computational work, the reasoning goes, requires lots of space. While I am not denying the importance of brains for intelligent behavior, there is one major problem with this line of though: some animal species display highly intelligent behavior, while having brains one-tenth the size of your little toe.

So where do we look for an explanation of this anomaly?

Let me first state how we will not find it: by looking even closer at brains. Focusing on brain-to-body ratio, the number of neurons, the amount of connections between these neurons or how densely they are packed, all these proposed “solutions” have proved to be insufficient. The answer, rather, is to be found outside the brain, in the bodies of animals. The eyes, and visual perception in general, play an especially big part in cognition.

What eyes are for

To appreciate how eyes can be a part of thinking or cognition, we have to ask what eyes are for. Why did they develop? And why are there so many different kinds of eyes? Normally, lay people and scientists alike consider the eyes as passive receptors that simply process incoming light. However, if we look closely at the different kinds of eyes that exist, we can see how they give rise to intelligent and complex behavior. To appreciate this, we should conceive of the eyes as active organs, rather than passive receptors. That is, we have to look at how eyes are used in the real world. Input is never just input, but acquired or sought for input.

When we embrace this view, we notice that eyes developed to detect different features of the environment, with different animals detecting different kinds of “energy” and in different ways. Moreover, this detection directly guides behavior; after receiving visual information, animals act on that information, they move so as to change what they see. In philosophy, the approach that studies the active use of the body and the senses in cognition, is aptly called “embodied cognition”. Embodied cognition provides vital insights into the nature of cognition and perception. And while there is more to bodies and cognition in general than just eyes, eyes are definitely important and – quite ironically – commonly overlooked.

Small-brained creatures: vipers and bees

Human beings can only see “visible light”, electromagnetic radiation with a wavelength between 400 and 700 nanometers. While the word “visible” nicely illustrates how preoccupied we humans are with ourselves, there are animals that can see electromagnetic radiation of different wavelengths. Pit vipers, for example, are able to detect infrared light. They do so with the infrared-receptors that are located between their eyes and nostrils. These receptors allow them to easily find prey, because the body temperature of living organisms is higher than the temperature of the environment. This means that, while humans can be misled by camouflaging colors and can mistake, say, a branch for a worm, vipers are never fooled. As a result, pit vipers do not need to plan or consult their memories to find food – the evidence that there is a living animal is right there, in their perception of the world. As philosophers say, the “cognitive load” is partly carried by the viper’s visual organs. The planning and remembering that we would normally ascribe to brains, is in this case achieved by the viper’s infrared receptors.

“While humans can be misled by camouflaging colors and can mistake, say, a branch for a worm, vipers are never fooled.

Now, vipers are not the only species in the animal kingdom with stunning visual perception. Consider another species: honey bees. These bees have even smaller brains than pit vipers, yet they are known for their exquisite sense of direction and their abilities to find the “right” flowers to pollinate. How do they do this? Once again, we have to consider what it would be like to see as a bee. Bees can detect three light phenomena that humans cannot: ultraviolet light, iridescence and polarized light.

The first phenomenon is light of longer wavelengths than humans can see: ultraviolet light. This allows bees, quite literally, to see the color of nectar. What looks like a dull yellow flower to human eyes is far more interesting for bees. The ability to perceive ultraviolet light means that they perceive the center of such flowers to have a purple-like glow, which gradually fades into bright yellow at the ends. At least, that is the best job I can do in helping you visualize it. Bees unmistakably see the presence of nectar on flowers.

But that is not even the most fascinating part. Bees are also able to detect a phenomenon called “iridescence”. Iridescence is the play of colors you can, for example, detect on soap bubbles. The next time you happen to be in the presence of a soap bubble, notice how it changes color depending on your viewing angle. This is as close as we can get to imagining what it is like for a bee to circle around a flower. The petals of different flowers show characteristic iridescent patterns. Thanks to this intriguing ability, bees immediately recognize the type of flower they have chosen to pollinate.

Now you might wonder: how do bees find these flower in the first place, if they are miles and miles away? Look at the sky outside. What do you see? On a clear day, it appears to be entirely blue. Not if you are a honey bee, though. Bees can see the polarization of the sky. Polarization is the changing pattern of colors that is created by particles in the air scattering the photons emitted by the sun. This acts as a compass to bees; as long as even the tiniest patch of sky is visible, they can use it to guide their long-distance travels.

Big-brained mammals like us would need considerable memory storage and probably some technological devices to do what a bee does naturally with a brain the size of a sesame seed. As we have seen, this is simply because the cues are literally in their field of view. To be sure, bees need to remember some stuff, but remarkably less than a human being would to achieve the same behavior.

It’s the eye of the spider

My hope at this point is that you are at least agnostic, and that my final tiny-brain-smart-animal example – which involves spiders – will pull you over the edge. Whether or not you like spiders, their eyes are extremely interesting. Portia spiders are a species of spider that are known for taking large detours through forests to catch prey. As they have brains the size of a pinhead, this is somewhat surprising. They should have been completely and utterly stupid, if we follow the brain-only assumption. A brief lesson in portia spider eye anatomy helps to understand the ins and outs of the matter.

Porta spiders have eight eyes. Six so-called secondary eyes and two bigger primary eyes. The former detect movement, while the latter are for distinguishing color and fine detail. Each of the primary eyes consist of a lens, attached to a kind of tube and then another lens. The second lens magnifies the image of the first one. They effectively see a very small patch of the world, analogous to shining a flashlight in the dark. But that’s not all. The light that enters their eyes splits up into different “layers” stacked one after the other in the eye tube, depending on wavelength or color. The portia spider can move its eye tube around the first lens, which allows it to focus on a particular wavelength. Say it wants to catch an ant at a distance in the forest. Before “tuning into” the ant, it performs advanced scanning behavior of its environment, after which it will strike. Then, with their intricate eyes, portia spiders can focus on just that ant (which gets magnified) and exclude all the irrelevant, distracting other colors that make up its environment. Its whole visual field, then, consists of the ant – nothing more and nothing less.

The eyes of pit vipers and honey bees, but especially those of porta spiders, illustrate that eyes can filter out irrelevant information before it is sent to the brain, or provide visual information that humans can’t directly obtain. To be sure, animals always need some kind of brain to process visual information, but eyes can already account for a big part of planning, focusing, remembering and a whole lot of other cognitive processes. Everything these animals need to know is right in front of them, so they can immediately act on it.

We are animals too

“Sure,” you might think, “some animals have complex eyes to compensate for their tiny brains. But us humans, big-brained creatures that we are, we do not need that.” However, considering the importance of eyes in small-brain creatures like pit vipers, honey bees and portia spiders would not it be illogical to dismiss this importance in big-brained organisms? Do not get me wrong: brains are very important for intelligent behavior, but why should the brain take over everything in organisms with relatively big brains? If brains indeed did take over the whole cognitive load, we would need a double explanation: one for small brains and one for big brains. This seems very counterintuitive to me.

Think for a moment about that big-brained, tentacled animal that is said to be the most intelligent of the invertebrates: the octopus. Apart from the fact that their nervous systems are downright alien (the majority of its neurons are located in its arms, and the rest is split between the “central brain” in its head and the “optic lobes” behind its eyes), their eyes are extremely complex and intriguing. Octopus eyes evolved separately from vertebrate eyes. When light hits their eyes, it is not focused into a single point (like in humans) but scattered into different wavelengths (or colors). Octopuses can adjust the depth of their eyeballs in the eye sockets, as well as the distance between the lens and retina. Due to this ability, octopuses can focus on particular objects by tuning into a particular wavelength. Surrounded by the darkness of the deep sea, such eyes come in handy. So, while octopuses have big brains that do contribute to their intelligence, the way they use their eyes also plays a crucial role in their cognitive behavior. Without these eyes, even those big octopus brains would be groping in the dark.

“The way that we perceive the world through our senses and how that shapes our thinking processes, is the only one way amoung a huge variety of possible ways.”

Naturally, we arrive at a final species: homo sapiens. My guess is that most people assume that our eyes are somehow “neutral” and our vision likewise. We just perceive the world as it is – simple as that. After discussing just a couple of different kinds of eyes, this perspective seems naively simplistic. Eyes, and other human and nonhuman animal sense organs as well, are organs that animals actively use, and humans – as animals – are no exception. At this point, you probably wonder: so, do we also think with our eyes? And if so, how? The answer to the first question is obviously “yes”. The second I will leave for you to ponder. But think of this humbling fact: the way that we perceive the world through our senses and how that shapes our thinking processes, is only one way among a huge variety of possible ways. We are not at the center, and it is time to start seeing this.