We all know the basic five senses of taste, touch, smell, sight and sound, and science tells us there are more, but do we really have 20 senses? And importantly, what does all this categorisation do to our ability to perceive?
From birth, and before, we turn data into information using our sensory system. This allows us to create order out of chaos; to make sense of reality. Taste is a classic example.
Even within types of senses we divide data into categories. You may have seen a map like the one shown here for the human tongue: sweet, sour, salty, bitter, and that strange one called umami, which allows us to recognise glutamates in foods. It is a kind of savoury taste. And now there are other tastes recognised as well, such as a fatty taste.
However, the idea that the tongue is divided up neatly into zones is actually a misrepresentation of the landmark paper published in 1901. Actually, although there are intense regions for taste, the types are not restricted. Try a test for yourself, using a cotton bud dipped in salty water or in lemon juice.
Taste also occurs within the mouth and throat, and although we are not consciously aware of it, there are even taste receptors present in the gut.
Okay, so taste is one type of basic sense. What are the others? Here is a list, divided up into those directly associated with sense organs (first 12) and those based in more complex perception (final eight):
Sound (although echolocation is rare, humans can train for this)
Smell (varies between individuals, e.g. some of us can't smell the 'drying garbage smell' of the Australian white ibis)
Taste (sweet, sour, salt, bitter, umami [savoury], fatty, metallic, pungent [spicy], chemical coolness, and numbness)
Touch (includes hard, soft, smooth, rough, and pressure)
Magnetic (often subtle but appears to be possible)
Proprioception (awareness of position, orientation [in space] and balance)
Stretch (sensed through both skin and muscle)
Motion (acceleration: linear or rotational)
Temperature (hot to cold)
Nociception (pain through localised tissue damage)
Interoception (related to body-sensing: oxygen quotient, thirst, hunger, nausea, clamminess, heart rate, blood pressure)
Temporal (passage of time)
Agency (interaction, influence or control)
Familiarity (awareness of)
Certainty (level of sureness or doubt)
Sexual (specific case of arousal)
Well-being (positive or negative state of being)
Mind (awareness of self, will and imagination)
Even without including these final eight, there are still significantly more than the basic five senses.
What is perhaps more interesting is how creating categories, especially within the major sensory types, can distort the way we perceive the world around us. The most notable example of this is the way that learning about different colours can affect the way we see them.
Researchers have looked at the visual ability of different cultures for many years. To explore this in a narrative form, the BBC mocked up a kind of field lab using a tribe called the Himba, that lives in northern Namibia. When presented with a computer screen showing a colour wheel of green squares, members of this tribe quickly picked out a slightly more yellow-green square amongst the other green squares. By contrast people from an Anglo or Western culture found that it took them longer to perceive the odd one out.
Do the Himba have structurally different or superior eye physiology? Indeed not. It appears to be their use of language that focuses and trains this visual attention. Since they use the word borou for both blues and blue-greens (they have no specific word for blue on its own), and dumbu for green-greens, reds and browns, their attention is focused more on distinguishing shades of green than shades of blue. The English language has less of a focus on yellow-greens as a category, unless you are an artist.
You can try for yourself to see how you go, time-wise, at distinguishing greens from yellow-greens. Here is the colour choice as a wheel, and here is where you can see the answer. Sadly, the original BBC documentary that took us into the mocked-up field laboratory is now unavailable, but some screen shots are still able in an article by Brian Oaster.
The lesson to be drawn from this story is that we see that which we train our mind to see. This means that we can miss things because we do not expect them to be there. The term used for this issue is hypocognition (meaning lack of recognition) and it makes for a fascinating subject in itself.
As for answering the first question, it appears that yes, we do have 20 senses; and when advances in technology are factored into our lives, we are capable of sensing even more.
Till next time – B.W. Cribb