Our senses create our reality. They enable us to navigate our everyday lives and make meaning of the world. As neurobiologist André White explains: “Our senses are an internal representation of our external environment.”
Most of us learn that we have five senses – sight, hearing, smell, taste and touch – each associated with a specific organ (eyes, ears, nose, mouth, skin). But it turns out we have at least seven senses, some argue as many as nine, with receptors held in different parts of our body.
Our sixth and seventh senses – Vestibular and Proprioception – may sound unfamiliar to most of us. Yet once I learned their function, I couldn’t imagine living without them. More than any others, these senses highlight how consciousness is central to our everyday experience.
Learning about the senses is being in awe of our bodies and minds. After reading this, you might watch a sunrise, listen to music, taste your coffee, and feel your body with a newfound appreciation. It’s also a dizzying reminder of the subjectivity of reality. Patrick Cavanagh, a neuroscientist and co-founder of the Vision Sciences Lab at Harvard, emphasizes:
“It’s really important to understand we’re not seeing reality. We’re seeing a story that’s being created for us.”
Reality is a lot more wiggly than it seems. It’s formed from a combination of external stimuli and internal response, which varies for each living being. Our brain is constantly filtering out most of the sensory information, only providing us with what it deems useful. This mechanism protects us from getting overwhelmed. It also means that what we perceive as reality is only a tiny glimpse of the whole picture. Our senses are the lens, our brain the aperture… So, can we open up?
Cover Image: "Seven Senses” video montage by me.
Polar bears are not white, their fur is transparent. Their hair shafts contain many tiny air bubbles which scatter the sun’s white light, which our eyes register as white fur.
Color doesn’t occur in the world but in our mind. Some animals see in black and white, while others can perceive colors invisible to us. What we perceive is unique to us and not a factual representation of the world.
In fact, our eyes are never able to see what is happening now, so our brain makes up for that delay. Neuroscientist Adam Hantman explains:
“The dirty little secret about sensory systems is that they’re slow, they’re lagged, they’re not about what’s happening right now but what’s happening 50 milliseconds ago, or, in the case for vision, hundreds of milliseconds ago.”
The brain predicts what will happen before it actually does. When someone throws a ball, our sight isn’t fast enough to follow its movement in real time, so our brain makes quick calculations on where it might land. It tells us a story about the nature and trajectory of objects, and this story becomes our reality.
To craft a narrative, our brain can’t just rely on sight so it uses our memories, emotions and experiences to predict reality. In other words, we see what we expect to see. But sometimes, the information doesn’t match the prediction. That’s where optical illusions – and bias – come into play.
My favorite book about seeing is also about art. And this optical illusion book is beautifully designed.
Sounds are rapid changes in air pressure, which our ear sensors perceive and send to our brain to interpret as sound. Hearing is our fastest sense. It takes our brain at least 0.25 seconds to process visuals, but only 0.05 seconds to process sound. The reason for this speed is survival. When our ancestors slept in the woods at night, the ability to hear sounds when they couldn’t see was critical to their livelihood.
Like our other senses, hearing is an editing experience, leaving out unnecessary and unpleasant information such as echoes. But hearing is also considered our most “honest” sense since it can’t easily be tricked. There are no auditory illusions in nature. The only audio paradoxes are created by technology.
To learn more about our sense of hearing, I recommend listening to this podcast and watching this film.
Molecules fly in the air, find their way to the receptors in the back of our nose, which our brain interprets it as a smell.
For a long time scientists assumed that the shape of the molecules matched the receptors in our nose – a sort of lock and key model. But that theory was abandoned in recent decades as we discovered there are far more smells (over a trillion) then receptors in our nose (about 400).
Smell is actually much more complex than that. Our smell receptors can change their shape and they each have their own smell preferences. Some are attracted to a certain type of scent, while others might prefer a certain molecule shape. When a molecule and receptor meet, they can also alter each other. Some of our receptors might bend flexible molecules, giving them a new shape. While others might be taken over by the molecule. It appears to be a sort of dance where one leads and the other follows, and both are transformed in the process. The result is that different people can smell the same exact thing and experience different scents.
To learn more about smell, I’ve recently been reading this book.
Until recently, we thought our sense of taste consisted of four distinct categories: sweet, salty, sour and bitter. Each taste is organized in different areas of our mouth: sweet at the tip of the tongue, bitter at the back, sour on the sides, and salty spread all over but mainly in the front.
Each taste bud guides us in our nutritional needs. Sweet is a signal for calories and sugars. Salty lets us know there’s sodium, an essential mineral. Sour is a response to unripe foods. Bitter is to warn us of poisonous foods. The bitter taste buds are located in the back of our throat to make us gag and protect us from ingesting the wrong foods. But poisons at low levels can also be medicinal, so bitter taste also helps us identify medicine. It also explains why bitter foods – such as coffee, olives or beer – can be an acquired taste overtime.
What we most often call “taste” is actually “smell.” The two senses share a common airshaft and the aroma makes contact with our nose before our taste buds experience it. When we’re unable to smell, our food experience becomes greatly minimized.
If you pinch your nose and taste cinnamon, it’s bitter. But with our sense of smell, it becomes a more complex flavor. We also use other senses in our food experience. We can’t taste spicy foods. The spicy molecules actually activate the pain and heat receptors of touch.
In recent decades, there’s been a debate around the discovery of a potential fifth taste: Umami. Foods that are considered umami are rich in glutamate (MSG), which includes cheese, mushrooms, seafood and seaweeds.
The scientific community resisted the existence of a fifth taste, until it was discovered that humans have a specific taste receptor for glutamate, making Umami an official taste. The journey of Umami has opened up the possibility and search for new tastes.
To learn more about the discovery of Umami, I recommend listening to this podcast.
We are creatures of touch. In one of my favorite books – A Natural History of the Senses by Diane Ackerman – I learned that babies deprived of touch are deeply affected in their development, both mentally and physically. Even if they receive other necessary care, such as food, water, warmth, some children will stop growing altogether.
The book explains: “Touch reassures an infant that it’s safe; it seems to give the body a go-ahead to develop.” Some tests done on baby monkeys also confirmed that “a relatively small amount of touch deprivation alone caused brain damage.”
We experience touch through our largest organ – skin. We have many skin sensors which give us a wide range of information: temperature, texture, pain, etc. Touch is what helps regulate our nervous system, giving it the appropriate signals of safety. It shows how the “healing power of touch” has real and long-lasting implications.
I was intrigued by the “Tactile Dome” in San Francisco, which is currently closed due to Covid restrictions.
I’ve simplified this sense to call it “BALANCE” in my monthly curation of Seven Senses.
We start gaining this sense once we can hold up our heads as babies. The vestibular system allows us to synchronize our eye movements with our head movements. It influences our balance, equilibrium, our ability to coordinate both sides of our body, as well as some aspects of language. It tells us which direction we’re moving in and informs us of our body position. In other words, it’s our internal GPS system.
Our vestibular sensors are located next to the cochlea in the inner ear. When our senses get conflicting signals, we experience motion sickness, dizziness or vertigo. When we’re on a boat, our eyes tell us we’re going in one direction but our vestibular system says otherwise – which can cause sea sickness. Falling asleep in cars, even if we’re in the driver’s seat, is also a form of motion sickness called sopite syndrome.
To learn more about our vestibular system, you can listen to this podcast.
I found our proprioception sense to be the most perplexing. In some ways, it’s similar to our vestibular system, but it has its own incredible function.
In Seven Senses I call it “ENVISION.” But I also think of it as “self-awareness.” Proprioception is our ability to know where we are in space.
Someone without proprioception cannot touch something without looking at it. They don’t have the spatial imprint to tell them where the object is. And this isn’t limited to outside objects – the same goes for their own body.
In an experiment conducted at the National Institutes of Health, people without proprioception were asked to touch their nose. If they could see their nose, they could touch it. But once the lights were switched off, they couldn't locate their nose anymore and ended up touching another part of their face.
Without proprioception, one cannot walk, stand, or even sit in the dark or with closed eyes, or else they’ll fall. They have to rely on their other senses, mainly sight, to inform them of their position, balance and movements. One patient describes that when she closes her eyes, she “feels lost.”
How does proprioception work? The 2021 Nobel Prize of Medicine was awarded to Ardem Patapoutian, a scientist who discovered a receptor called Piezo2. This receptor is responsible for feeling light touch and informing our muscles of how far our limbs are from each other. And it’s the missing receptor for people without proprioceptive sense.
For more insight on this bewildering sense, listen to this podcast.
Making Sense of Ourselves