Neuroscientist Dr Lisa Feldman Barrett delves into the different ways we’re able to perceive the world that go beyond sight, sound, touch, taste and smell.
How many senses does the average human have? Assuming you equate senses with their receptors, such as the retinas in your eyes and the cochlea in your ears, then the traditional answer to this question is five – seeing, hearing, touch, smell and taste.
They’re called the ‘exteroceptive’ senses because they carry information about the external world.
But your body also has receptors for events occurring inside you, such as your beating heart, expanding lungs, gurgling stomach and many other movements that you’re completely unaware of. They’re traditionally grouped together as another sense, called ‘interoception’.
Yet a proper answer to this question is even more complex and interesting. For one thing, your body has receptors to carry other types of information, such as temperature, that we don’t usually consider to be senses.
Also, some of your receptors are used for more than one sense. Your retinas, for example, are portals for the light waves you need for vision, but some retinal cells also inform your brain if it’s daytime or nighttime. This unnamed ‘day/night sense’ is the basis for circadian rhythms that affect your metabolism and your sleep/wake cycle.
Even senses that seem fundamental, such as vision, are intimately entwined with other senses that seem separate.
For example, it turns out that what you see, and how you see it, is yoked to your brain’s tracking of your heartbeat, which is part of interoception.
In the moments when your heart contracts and pushes blood out to your arteries, your brain takes in less visual information from the world.
Your brain also constructs senses that you don’t have receptors for. Examples are flavour, which the brain constructs from gustatory (taste) and olfactory (smell) data, and wetness, which is created from touch and temperature.
In fact, your brain constructs everything you see, hear, smell, taste and feel using more than just the sense data from your body’s receptors. Light waves, for example, don’t simply enter your eyes, travel to your brain as electrical signals, and then you see.
Your brain actually predicts what you might see before you see it, based on past experience, the state of your body and your current situation. It combines its predictions with the incoming sense data from your retinas to construct your visual experience of the world around you.
Similarly, when you place your fingers on your wrist to feel your pulse, you’re actually feeling a construction based on your brain’s predictions and the actual sense data. You don’t experience sensations with your sense organs. You experience them with your brain.
