It’s curious to think that my brain is blind, deaf and mute. It can’t in fact sense anything, except if you get in there and prod it. Since I was an embryo, it’s been locked up inside a prison of bone. To build a mental image of the world, including of course an image of my own body, my brain must rely on electrical signals fed it by my body’s nervous system. Nerves in my eyes and skin tell my brain what they’re detecting. That nerve data is interpreted every squillisecond to construct a dynamic model that hopefully corresponds to reality.

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If that data is reliable and my brain’s interpretation is accurate, my perception of the world is accurate. Brain gets told about changes in the light and sound. Interpretation: the frisbee is coming towards me. Brain sends orders back. Brain gets told arms and legs are moving. Brain makes more orders. Brain gets told hands have caught frisbee. Brain happy.

On the other hand, if my nerves are faulty or misled, or my brain puts it together wrongly, my perception is distorted. Brain gets information about light and sound. Interpretation: it’s safe to cross the road. Brain gives orders. Changes in light and sound detected that are consistent with body moving. Brain given new data suggesting body is in middle of road. Brain experiences complacency leading to laziness. Brain distracts itself with thoughts of bakery. Brain omits to incorporate some nerve data. A second later, brain deafened by overwhelming urgent nerve messages- sound, sight. Interpretation is confusing, then suddenly crystal-clear: vehicle approaching body at alarming speed. Brain blames nerves for not passing on the message. Blame the least of brain’s worries.

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How do I know what exists? How can I tell what’s happening right now? I have faith in my nerves and my brain’s ability to analyse. I can’t corroborate their information against any other data set. I can only detect other data sets via the data relayed to me by my senses. I must trust them. I am utterly dependent on them. I truly live by faith.

So what channels the sources of my knowledge? Only my senses. Everyone knows there are five senses, right? Sight and sound; smell, taste and touch. The traditional five-strong list is attributed to Aristotle. But even puny, blinkered, unobservant humans have more than five senses. How best to categorise them?

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1. Exteroceptive senses. To do with external stimuli. Eight in number: sight, taste, smell, touch, temperature, hearing, balance, pain.

But Sight is really two senses: the sensations of colour (the frequency of photons of light) and brightness (amplitude/intensity – number of photons of light).

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Taste and smell are our two chemical senses. Together they form chemoreception. Taste plus smell equals flavour.

Some say the taste sense (the marvellously-named gustation) is really five senses, because they answer to different parts of the brain. There are the four well-known ones- sweet, salt, sour and bitter, plus a sensation called umami, which detects the amino acid glutamate, found in meat, soy sauce and in monosodium glutamate (MSG).

In the West we don’t use much MSG, except in processed food. In China, it’s commonly sold in packets like sugar and added in cooking. This white powder is somewhere between salt and flour in fineness. To me its rich savoury taste is more like salt than anything else, but without the mineral hardness of salt.

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Smell (olfaction) is the detecting of airborne (or waterborne) volatile chemicals. These odorants dissolve in the mucus of our nasal cavity and stimulate olfactory sensory neurons in our olfactory epithelium. Humans have 10cm2 of this olfactory epithelium. Some dogs have 170cm2 of the stuff. If you thought your tongue was doing well being able to detect five groups of taste, your nose can distinguish hundreds of different substances, even with a cold.

As part of your sense of smell, your body has a separate system called the accessory olfactory system. You mainly use it to detect pheromones. It lets snakes smell prey, and lets humans do the following things. It strengthens women’s sense of smell during ovulation. It lets humans detect blood-kin, but not spouses, by smell. It lets mothers identify blood-children, but not step-children by smell. It lets pre-adolescent children identify full siblings, but not half-siblings or step-siblings by smell. All this helps in family-building.

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Touch (tactition) is basically sensitivity to pressure. Based on the complexity of the pressure pattern, we can discern sharp, blunt, rough, smooth etc. Itching is triggered by itch-specific neurons.

We also have thermoception, or sensitivity to temperature. The receptors for this are mostly in the skin.

Hearing (audition) happens when we sense the vibrations from sound waves in the medium hitting us, and so in a way resembles touch more than anything else, which is why we ‘feel’ high and low frequencies. Deafness is apparently the only degeneration it’s still ok to laugh at. The echolocation of bats and whales is the interpretation of reflected sound.

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Balance, or equilibrioception, is made up of angular momentum and linear acceleration. This is inner ear stuff. You can tell body movement, direction and acceleration.

Our sense of pain (nociception) comes from mechanical, thermal or chemical changes beyond a set threshold. The pain receptors are mostly in the skin and on internal surfaces, less so in deep internal places. The reason this is classed as its own sense is because nervous activity signalling tissue damage and the psychological response of pain to this physiological event are two separate things.

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There’s more

Like our sense of pain, many of our self-analysing senses produce fun sensations we can be consciously aware of:

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2.  Interoceptive senses, our internal senses, do the following things:

-Stimulation of sensory receptors in the esophagus result in sensations felt in the throat when swallowing, vomiting, or during acid reflux.

-Sensory receptors in pharynx mucosa, similar to touch receptors in the skin, sense foreign objects such as food that may result in a gag reflex and corresponding gagging sensation.

-Stretch receptors in the gastrointestinal tract sense gas distension that may result in colic pain.

-Stimulation of sensory receptors in the urinary bladder and rectum may result in sensations of fullness.

-Pulmonary stretch receptors are found in the lungs and control the respiratory rate.

-Cutaneous receptors in the skin not only respond to pressure and temperature, but also respond to vasodilation in the skin such as blushing.

-Stimulation of stretch sensors that sense dilation of various blood vessels may result in pain, for example headache caused by vasodilation of brain arteries.

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3. Proprioception (Latin proprius, meaning “one’s own” and perception):  The sense of the relative position of neighbouring parts of the body. Awareness of movement derived from muscular, tendon, and articular sources.

There is conscious and unconscious proprioception. This sense is what American police officers test when they ask you to touch your nose with your eyes closed. You use it to walk in the dark without falling over. It lets you drive a car or run without looking at your feet, or to write without guiding your hand with your eyesight.

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Needless to say stuff like ‘sense of humour’ and ‘sense of time’ aren’t really senses. We perceive time but we don’t sense it. The perception of time is something the brain does with the information it has already been given by the real senses.

How many senses was that? About 21, just ones humans have.

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Other organisms:

We (I assume only humans will be reading this) can only detect electromagnetic (EM) waves in what we have self-suitingly called the Visible Light range. Some snakes- pit vipers, pythons and some boas- can detect EM waves in the infrared range, ie they can see heat. It’s not fundamentally different to our sense of temperature, except for being vastly more sensitive. The infrared radiation is detected by the skin inside pits on the snake’s face. From this they sense the distance and direction of the heat source. Birds and bees can see UV light. Bees and some squishy things like cuttlefish and squid can see polarised light.

Some animals –sharks, rays, some fish- have electroreception. So do some monotremes, such as the platypus. Having that would be cool.

Magnetoception: some birds, insects and bacteria can detect fluctuations in magnetic fields. This turns out to be jolly handy for navigating, and combined with feathers, lets birds migrate from one region to another as the seasons change.

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Given the number of senses we barely sense we have; and the senses we lack that other organisms possess; and the additional number of possible other senses, is it not possible that there are entire realms of reality we cannot sense? I’m not speaking now of other dimensions, but information technically available within our own familiar dimensions. When we can’t possibly see a thing, like a quark or a photon, we move on to other ways of detecting it. What happens if we go through all the possible senses, and there is still information out there that we aren’t able to sense?

Our senses are aimed at the material realm. Is it not possible that there is a non-material realm with as many varieties of stimuli as there are for our material ears and noses and tongues? That realm is outside nature, the remit of science. It is literally super-natural. It is the spiritual realm.

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Materialists shudder. You might object that there’s no hard evidence. But of course, you’re thinking about the kind of evidence our material senses work from. The non-material, spiritual realm might offer no material data, no more than freshly-baked bread would offer the ears an aroma; no more than your eyes would see the smooth sound of Marmite. It’s another literalism: non-sensical. What you’re asking for is material-spiritual synaesthesia. Not that bread or Marmite don’t broadcast stimuli: only that we can carelessly use the wrong instrument to seek that stimuli, like a bomb-disposal expert sold a duff instrument that can’t detect bombs. Faith is blind, but reads Shakespeare in Braille.

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