Sensory Perception Archives

Humans are not the only creatures processing numerous streams of sensory data in order to determine what’s out there in the world and what to do about it. Many of the animals and insects we share the planet with are doing the same thing, of course, some with very different capacities from ours: more taste receptors, wider ranges of hearing, and even sensory systems we don’t have. They inhabit the same physical world we do, but their experiences are vastly different from ours because they have different or different-capacity receptors.

What you are able to experience is completely limited by your biology. This differs from the commonsense view that our eyes, ears, and fingers passively receive an objective physical world outside of ourselves. —David Eagleman, Incognito

What You See Is…What You See

When it comes to visual perception, jumping spiders can see a broader spectrum of light, and geckos have vastly superior night vision. The vision of eagles is eight times sharper than human vision, making it possible for them to track prey from a mile away. Cats and dogs see only two colors, but butterflies and rats see ultraviolet and reptiles see infrared light, both of which humans can’t see.

Then there are bats, who in spite of their reputation, are not really blind. They just have very small and very sensitive eyes that operate effectively in extreme darkness. Their vision isn’t as sharp or colorful as human vision because they don’t need that. On the other hand, they have a sense we don’t: echolocation. According to the National Park Service:

[Bats] produce sound waves at frequencies above human hearing, called ultrasound. The sound waves emitted by bats bounce off objects in their environment. Then, the sounds return to the bats’ ears, which are finely tuned to recognize their own unique calls.

Bats use echolocation for hunting, but also for searching and “social calls.” Each species has its own call, and they can change their calls depending on the purpose. You can hear some bat sounds here. Bat calls sound sort of like birds.

The Scent of Water; the Smell of Rain

Most people know that dogs have a stronger sense of smell than humans, but there are claims that the sense of smell of African elephants, who need to drink 70-100 liters of water a day, is even stronger. They have about 2,000 olfactory sensors and five times as many genes for smell and supposedly can detect water sources over 10 miles away. But water is odorless, so what do they actually smell? There hasn’t been much research to date, but results so far suggest elephants might smell the VOCs (volatile organic chemicals) in the water.

As an aside, the smell of rain most of us are familiar with is called petrichor, a term coined by Australian scientists in the 1960s. Petrichor is a combination of water from the rain and ozone, plant oils, and a chemical called geosmin, which results when the first drops of rain interact with airborne bacterial spores. We can detect geosmin at less than 5 parts per trillion, which needless to say is an extremely small amount.

Other creatures that have a superior sense of smell include silvertip grizzly bears, great white sharks, kiwi birds, turkey vultures, and bloodhounds.

Hear, Hear

Moths, bats, elephants, owls, dogs, cats, horses, dolphins, rats, and pigeons all have hearing that exceeds the human capacity of 20 Hz–20 kHz. The greater wax moth can hear frequencies up to 300 kHz, 15 times higher than the highest pitched sounds we can hear.

While a human ear consists of three muscles and the three smallest bones in the body, a cat’s ears are controlled by around three dozen muscles per ear which allows them to rotate their ears 180 degrees. Cats are able to stalk small, fast prey in low light, so they have to be able to hear sounds that are quiet and that have a higher pitch. They can hear sounds almost two octaves higher than humans can detect and an octave higher than dogs. (So should dog whistles really be called cat whistles?)

Our African elephant friends, on the other hand, can hear and communicate via infrasonic sound which is in a lower range (14 Hz to 16 Hz) than humans can detect. The wide-set ears on their large heads funnel in sound waves from the environment

Cookie Monster Kitty

When it comes to taste, pigs and cows have more tastebuds than humans, 15,000 and 25-35,000, respectively, compared to our 10,000. Both pigs and cows are herbivores and the additional tastebuds help them distinguish poisonous from nonpoisonous plants. So all those additional tastebuds definitely aid in their survival. Birds, on the other hand have far fewer tastebuds than humans. Chickens have only around 30.

It’s not just the number of tastebuds that determines how things taste to animals or humans. Cats don’t have tastebuds for sugar because sugar isn’t important for their survival. I did have a cat many years ago who was really into Stella D’oro cookies—the variety pack that you can’t get anymore. The cookies weren’t safe even when they were in a covered container. She once leapt into the air and grabbed one out of my partner’s hand as he was in the process of trying to take a bite of it.

Carnivores, including dogs and cats, have tastebuds at the tips of their tongues that are especially attuned to water. And catfish have their whopping 175,000 tastebuds spread all over their bodies, skin, and fins. They can detect a taste in the water from miles away. They need this ability to help them find food because the murky water where they hunt has such low visibility.

Reach Out and…

While catfish can taste at a distance, manatees can touch at a distance. Instead of tastebuds, a manatee’s body is covered with tactile hairs that allow it to feel objects without coming into contact with them, even if those objects are not nearby.

Seals have such finely tuned whiskers they can track fish that are more than 600 feet away in murky water. The nearly-blind star-nosed mole has a nasal appendage covered in 25,000 sensory receptors (compared to 17,000 in a human hand), as a result of which it is the fastest-foraging mammal in the world.

Sci-Fi Senses

As mentioned previously, some animals have senses humans don’t have, such as echolocation (used by dolphins as well as bats), electroreception (the ability to sense electrical currents or fields, used by aquatic and amphibious animals), or magnetoreception (the ability to perceive the Earth’s magnetic field, used by homing pigeons and pregnant sea turtles).

Our Experience is Not an Accurate Reflection of Reality

Whether an individual has a sensory processing disorder, a sensory enhancement, or better or worse sensing abilities than their fellow humans or other creatures, we all exist in the same physical world that contains the same material processes and properties. We do not, however, experience the world in the same way, which means our experience is not an accurate reflection of reality. We have receptors that provide us with the type and quantity of sensory data that is good enough, that is sufficient to allow us to be us, to experience specific aspects of the world (our umwelt, as biologist Jakob von Uexküll named it) but not others, to maneuver within that world, to mate and continue the species, to survive.

If our sensory capacities were different, our experiences would be different, and we would be different. As a thought experiment, try to imagine what your experience might be and who you might be if, for example:

You had the eyesight of an eagle that can identify objects a mile away
You had only 30 tastebuds
You could detect water a mile away
You had the hearing of a cat
You could feel objects without coming into contact with them

What would be the benefit or drawback of any of these—or other—altered sensory perceptual capacities? Is there a sensory capacity you, as a human, have that you’d be willing to trade or have modified for the sensory capacity of another creature?

I would definitely not want to have only 30 tastebuds or the hearing of a cat. I’m not too keen on being able to feel objects at a distance, either. That seems invasive and disruptive. I could take or leave detecting water a mile away; I wouldn’t be willing to trade anything to have it. The eyesight of an eagle is appealing, though. I imagine it would create expansiveness, the sense of inhabiting a larger world. I’m not sure I’d be willing to trade anything I already have to get it. I’ll have to do some writing and thinking about it.

Coming up soon: more on the umwelt and a shift from physiological processing to psychological processing.

Our brain is constantly weighing and calculating (interpreting) multiple internal and external factors and inputs to arrive at its predictions—all within the context of what is normal for us—to determine what is going on and to prepare our response.

The neural wiring that generates perception is not identical, person-to-person. One outcome of this is what we could consider a diminishment of perception (color blindness, face blindness, aphantasia, for example). An outcome on the other end of the spectrum of so-called sensory processing disorders is a supersense—not the superhero variety, but an enhanced ordinary sense.

Those of us who don’t have any super senses probably don’t think much about them. But surprisingly, 25% of the population has heightened taste sensitivity. These people, known as supertasters, tend to have more tastebuds on their tongues, and some have a genetic mutation of a receptor for bitter taste.

Other super senses are tactile hypersensitivity, which makes ordinary tactile sensations painful or bothersome, hyperosmia, enhanced sense of smell, which can be a result of genetics, a medical condition, or training, and hyperacusis, super sound, which is generally a result of disease or some other medical condition.

The Color Purple

Tetrachromacy is a genetic mutation that allows some people to distinguish 100 times more colors than the rest of us, which is mindboggling, given we can normally distinguish around a million different hues. But colors are not objective properties of objects in the world. Allen Tager, a Russian American artist and cognitive scientist, noticed that the color violet was virtually absent from paintings completed before the Impressionist era, beginning in 1863. He attempted to determine why this was the case. In reporting on his research in Aeon, he noted:

International surveys showed that people tend to be unsure about exactly what constitutes the colour violet. The same person who describes an object’s colour as violet today might describe it as purple, blue, magenta, fuchsia or burgundy tomorrow. Language plays a role, too—there’s a difference even between British English and American English. The colour beyond blue on the spectrum is called purple in the US, but violet in the UK. Reddish-purple is sometimes called violet in the US, but hardly so in Britain. The complete range of colours between red and blue is often called purple in British texts, but sometimes the word violet is used, too.

Neuroscientist Anil Seth points out that colors only exist in the interaction between our brain and the physical world. They exist neither out there in the world nor in here inside the brain. They are essentially constructed.

Several years ago, I used ink color to differentiate categories in a print document I shared with a number of other people. The shade of green I selected for one of the categories looked green to me both in print and on the computer, and the computer program identified it as green. But so many people saw it as a shade of brown or gray that I changed the color to something more obviously green. Consensus reality as determined by myself, the other people who saw green, and the computer program said that seeing green was the correct perception. But does it make sense to deem a different perception wrong?

People with hypersensitivities don’t tend to experience them as enhancements, meaning they don’t automatically enjoy them. Of course, if the cause is genetic, they have nothing to compare their experience with, just as those of us who don’t have a hypersensitivity have nothing to compare our experience with. But for the most part, moment-to-moment we have nothing to compare any of our experiences with.

Again, we can’t tell by looking at someone, whether or not they have any hypersensitivity, unless perhaps they’re in a situation where they’re confronted with a stimulus.

Additional Senses

The brain also receives additional sensory information beyond the five basic senses. Other sensory systems include vestibular (balance), proprioception (body position), kinesthesia (movement), nociception (pain), and thermoception (temperature).

Scientists are still trying to determine why people with red hair have differences in regard to pain threshold (lower), pain sensitivity (higher), and response to pain medication (higher or lower depending on the type of drug), but they do.

A friend I used to spend a lot of time outdoors with—walking, hiking, or lazing—would start seeking shade when the temperature approached 70 degrees, the point at which I was just starting to enjoy the warmth. She spent New Mexico summers inside with the air conditioner on and the blinds closed. I haven’t used indoor cooling for the past 10 years.

Including these additional five senses doubles the types of sensory data our brain is tracking in order to keep us alive and provide us with a sense of what’s happening to and around us in order to determine what we ought to do about it. Like the original five senses, we tend to take these senses for granted unless we begin having trouble maintaining our balance or we develop chronic pain, at which point the brain will bring the change in the status quo to our attention.

When you’re tempted to fall back on the belief that you experience the world as it is, try to imagine some of the millions of colors you can’t see…and name them.

The Scent of Water;
The Smell of Rain