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Touch is perceived as one of the most radical sensory engagements with museum collections

Linked to the other touch systems (balance, interoception, pain, proprioception and temperature), examining the tactile qualities of collections is a chance to learn more about them through close, physical contact.

Being afraid of tactile contact with museum collections wasn’t always a concern.

In the 18th century, museums were spaces to learn through tactility.

This began to change through the late 18th and mid-19th centuries, where socio-cultural, scientific and geopolitical shifts meant that the visual became the ‘preferred’ method of learning and engagement.

As working class people became more prevalent visitors, it was more about who was visiting, rather than what they were touching.

Into the 21st century, we still hold these values. By maintaining distance from our collections, we are likely missing out on a whole host of information we can sense through these direct tactile interactions.

However, while to touch is to potentially damage, there is so much potential in the ‘mechanoreceptive’ system, the last of our four ‘Somatosensory Systems‘.

Want to feel more confident about this system and its relationship to the other senses?

Watch the videos and/or read the transcripts below.

K & C Neurobiology ‘Mechanoreceptors’ (live transcript available on YouTube page) [3mins 49secs]
Transcript

There are four main kinds of mechanoreceptors, all of which can be found in different layers of the skin. They are the Merkel, Meissner, Ruffini and Pacinian receptors.

Merkel afferents, or Merkel’s discs are located in the upper skin, at the base of the epidermis.

  • In fact, they live on the primary epidermal ridges, which, on our fingers, make up our fingerprints.
  • They are responsible for about 25% of mechanoreception in the hand
  • They are densely populated and account for discriminative or light touch
    • Light touch is based on pressure and, due to small receptive fields, lets us sense fine details and edges, corners and curves
  • Merkle’s have the highest spatial resolution and therefore help us with identifying shape and texture
    • This is what lets us type on our laptops or find the right keys on the piano

Meisner’s corpuscles are found in the upper dermis, but occasionally project into the epidermis

  • Even more dense than Merkel’s, Meissner’s make up about 40% of the mechanoreception in our hands
    • They extend into the dermal papillae by the primary ridges and are therefore elongated
  • Made up of fluid-filled connective tissue, these afferents respond to low frequency vibrations, as well as fine detail touch and pressure
  • Their sensitivity is almost four times that of Merkel’s, but their larger receptive fields reduce this spatial resolution
  • They fire when the skin is indented, stretchingthe collagen fibres.
    • But since they work with low frequency, they can pick up textures that are subtly moved across the skin
  • This makes them valuable for detecting something slipping out of our hands

Pacinian afferents rapidly adapt making up 10-15% of mechanoreception

  • These are located deep in the dermis, almost into the subcutaneous layer
  • They are made up of many layers of membranes wrapped around just one afferent fibre
  • Because of the vast layering, Pacinians filter out low frequencies and only pick up high frequency signals
  • They even have higher adaptability and sensitivity than Meissner’s, but that means they have even larger receptive fields, giving them very low spatial resolution
  • They can sense impressions of only 10 nanometres, but they have no idea where that indentation is happening
  • For this reason, they are responsible for macro scale activities, like using tools, cutting, vegetables and writing

Ruffini afferents are the last class of mechanoreceptors

  • They are slowly adapting fibres and are located deep in the skin between the dermis and subcutaneous layers
  • They are also in the ligaments and tendons, making up about 20% of the mechanoreceptors in our hands
  • The Ruffini afferents run parallel to the stretch lines, making them responsive to skin stretch and movement
  • They are thought to play a role in the feedback mechanisms for gripping objects and they control finger position, movement and hand conformation

Though Merkel’s and Meissner’s afferents are more prevalent in the skin, all four types of mechanoreceptors are crucial for our sense of touch.


Mechanoreception is also linked to other ‘touch’ sensory systems.

Ted-Ed ‘The man who lost his sense of touch’ – Antonio Cataldo (live transcript available on YouTube page) [6mins 2secs]
Transcript

In 1971, Ian Waterman suddenly collapsed from a severe case of what seemed to be gastric flu. His illness passed after a few days, but a stranger set of symptoms lingered. Although his muscles and joints remained healthy, Waterman was unable to move. In fact, he was unable to feel anything from the neck down.

Eventually, he was diagnosed with a rare and extreme form of ‘deafferentation’, a neurological condition in which certain signals from the nervous system are interrupted or impaired. Without his body’s constant feedback on how his limbs were moving, Waterman was unable to sit up, stand, or walk. But over time, he taught himself to use sight to judge the distance of his limbs from other objects. And eventually he regained complete control of his body— so long as he could see it.

We often don’t think of touch as being a vital part of movement. But touch is just one part of the somatosensory system: a network that oversees all the sensations arising from the surface and interior of our bodies.

  • Touch, pain, temperature, and our awareness of our bodies in space – also known as proprioception – are regulated by this system, and when something goes wrong, the effects can be dramatic.
  • All these sensations are processed by millions of tiny receptor cells embedded in our skin, muscles, tendons, and organs.

Every square centimetre of our skin is packed with hundreds of these cells, and their shape, size, and depth determine what kind of stimuli they respond to.

  • Mechanoreceptors sense mechanical deformation of the skin.
    • This could be triggered by low or high frequency vibrations, a stretch, or simply light, static pressure.
  • Thermoreceptors respond to temperature changes, while nociceptors sense pain.
  • Proprioceptors sit deep in your muscles and tendons, continually detecting and relaying information about the position of your body.
  • Your brain then combines this information with other sensory data to move through space without needing to see your limbs.

All of these receptors work by sending electrical signals to the brain through fibres they’re attached to, and the speed of those signals varies with the fibre’s thickness.

  • For example, some nociceptors are attached to fibres with slightly more conductive, fatty myelin than others.
    • So when you get hurt, the electrical impulses from thicker nociceptors trigger sharp, intense pain, while thin, unmyelinated nociceptors are responsible for the dull, aching pain that follows
    • Since the fibres carrying tactile information are much thicker than those carrying nociceptive signals, rubbing an injury can produce temporary relief from the pain

These receptors generate a constant flood of signals that travel through the nervous system to the brain.

  • But if this process is disrupted – either by damage to the skin, the nerves, or the brain – the network breaks down.
  • And since it underpins so many bodily functions, damage to the somatosensory system can manifestin a wide variety of ways.
    • In Waterman’s case, an autoimmune reaction attacked a large swath of his nervous system, leaving him with no tactile or proprioceptive sensations from the neck down.

But deafferentation is just one of many somatosensory disorders. Individuals can receive damage to a specific brain area or a section of skin, resulting in the loss of certain sensations in particular locations. The impact of this loss can be significant.

  • Losing tactile sensations makes it difficult to gauge how much strength to use in a situation.
  • Without the warning signals provided by thermal and pain stimuli, we don’t react when our bodies are damaged.
  • And, being deprived of social touch can cause a condition known as touch starvation, characterised by anxiety, depression, high blood pressure, and even a weakened immune system.

Many individuals who face these realities have found innovative ways to adapt. But it’s undeniable that all these invisible sensations play a vital role in how we navigate the world – even if they can be difficult to put your finger on.

Your perception and experience of the ‘texture’ of things can differ, depending on whether:

  • You’re touching it (actual/tactile texture)
  • You’re looking at it (visual texture)
  • What it has been made to look like doesn’t match the tactile texture (implied texture).

While we are focussing on actual/tactile texture, it is important to notice whether it seems connected or disconnected to with the visual or implied texture.


This list is far from exhaustive, but gives you some useful starting points for thinking about how you might sense and record texture:

Hold
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  • Bouncy
  • Distended
  • Limp
  • Slippery
  • Solid
  • Spongy
  • Springy
  • Squashy
  • Turgid
  • Viscous
  • Watery
  • Wrinkly
Roughness
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  • Bristly
  • Bumpy
  • Dry
  • Coarse
  • Gritty
Shape
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  • Angular
  • Curvy
  • Bumpy
  • Lumpy
  • Sharp
  • Smooth
Sharpness
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  • Biting
  • Prickly
  • Scratchy
Smoothness
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  • Dusty
  • Feathery
  • Fluffy
  • Furry
  • Fuzzy
  • Hairy
  • Powdery
  • Silky
  • Velvety
Wetness
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  • Balmy
  • Gooey
  • Greasy
  • Moist
  • Oily
  • Slimy
  • Sticky
  • Sweaty

Let’s take the high stakes “we can’t touch the collections” out of the equation for the moment, and focus on something you are comfortable handling.

Safe touch

  • Choose something like a pen, some loose change, a mug (maybe one that is still full of a nice hot drink), that apple you keep telling yourself you’ll eat. Maybe try something bigger – a desk, your chair, the window, the floor?
  • Touch the item using different parts of your body
    • palm of hand, back of hand, forearm, lips, face, mouth etc.
  • Touch the item in different ways
    • stroke, press, use different pressure, lift, shake, hold, rub, grip, cradle, swing, push etc.

Don’t be afraid to work with a dictionary and/or thesaurus to help find the more exact terminology you need.

For example, check out the following page from ‘Writers Write‘, which has a helpful list of touch adjectives you may find useful: www.writerswrite.co.za/209-words-to-describe-touch/