Making sense of our number of senses
I've gone slightly off topic with this post, exploring our own senses. See what you think.
We often encounter the idea that human beings have a ‘sixth sense’ which gives us the ability perceive spirits and foretell eerie happenings. Our hairs stand up on our neck and a ghostly breeze makes our heart race as we connect with the ‘subtle dimension’. In reality we may have just left the window open, but nonetheless the idea of unrealised senses is an interesting one, and one that is not as silly as it seems.
Let’s start with thinking about what a sense is. Put simply, it’s a way in which we gather information from the outside world. When you look at a ball, light bounces off it, making it visible. This light is received by our eye (a sense organ) which sends a message to the brain and results in us seeing. However, the entire eye doesn’t communicate with the brain. The job is that of specialised sensory cells, called rods and cones, which send messages via connecting nerve cells.
Traditionally, we’ve been taught just five senses: sight, hearing, smell, taste and touch. These were established long ago, since the days of the philosopher, Aristotle. It’s not surprising that with less scientific understanding we initially comprehended only these five senses, as these are linked to very obvious features: eyes, ears, nose, tongue and skin. However, now we can argue that we have many more than five. In fact, some believe we have 21.
The number of senses we have comes down to how you categorise them. Three really simple categories can be made by considering the nature of the stimulus – chemical (tastes, smells, internal chemical changes) mechanical (touch and hearing) and light (vision) – but this would leave us with fewer than we started with.
On the opposite end of the scale you can use the scientific definition of a sense – a group of specialised sensory cells that respond to a specific signal and report to a particular region of the brain. In this way, the sense we think of as taste could alone be broken down into five different senses – sweet, salt, sour, bitter and umami, the latter of which is a Japanese word for the meaty taste of glutamate.
What we can probably say is that we certainly use more than five senses. For example, imagine that you’ve suddenly had a powercut and you’ve sadly stubbed your toe, leaving you to hop around in a dark room trying to avoid the cup of tea on the floor. You may not see this as a remarkable feat, but you accomplished this task without using your traditional five senses. In fact, you used a sense called nociception (pain), equilibrioception (balance), proprioception (awareness of where your body parts are) and thermoception (temperature) if you managed to hop into the hot cup of tea.
The senses I have already mentioned, including the traditional five, are exteroceptive senses, or in other words senses that perceive the body’s position, motion and state. Using the scientific definition I described earlier, there are also interoceptive senses which allow us to sense the physiological condition of the human body. These are linked to sensory receptors found in internal organs, such as those in the lungs that control respiratory rate.
If you start thinking about the range of animal abilities your eyes become open to even more senses in the natural world. Bats and dolphins use echolocation to see their world, and even some blind people have trained themselves to use it. Vampire bats and some snakes can see infrared and bees and dragonflies can see ultraviolet. By sensing magnetic fields birds can migrate great distances and sharks can sense changes in electric fields, such as those of their prey.
In conclusion, there can be almost no doubt that we have more senses than five from a scientific perspective, but the exact number does depends on the way you choose to categorise them. When you consider the wide range of specialised cells in our bodies that communicate all sorts of information to our brain when stimulated, the list could be rather long. Therefore, it turns out that the ‘sixth sense’ isn’t so special after all.
Photo by author ©Kate Dey, 2014.
Harvard Medical School, 2014, Extra sensory perceptions, written by Jessica Cerretani, [online], available at: http://hms.harvard.edu/news/harvard-medicine/extra-sensory-perceptions accessed 30 October 2014.
Lloyd. J. and Mitchinson. J., 2006, The book of general ignorance, Faber and Faber Limited, p.48 -49.
New Scientist, 2005, Senses special: Doors of perception, Issue 2484, written by Bruce Durie.
Scientific American, 2012, Making sense of the world, several senses at a time, [online], available at: http://www.scientificamerican.com/article/making-sense-world-sveral-senses-at-time/ accessed 30 October 2014
