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This article comes from the official account of Wechat: back to Park (ID:fanpu2019), author: Shuishui

In the past two years, there has been a big fire in the concept of meta-universe, which seems to be something that can change the future of mankind. Regardless of the business outlook, some researchers are indeed working to combine virtual reality with digital life. There is a question: can you experience the same cold, hot, sour and sweet feeling as reality in the virtual world? Chemical touch may tell us the answer.

The alarm sounded suddenly, and he quickly left the scene. As soon as he got to the exit, there was a sudden explosion, and the spark splashed on him, which made him feel tingling. When he came outside, there were snowflakes in the sky and a chill came, and he found that it was an alarm from the nearby nuclear reaction room. When he went to explore, he found that his arm was paralyzed and weak, so he finally opened the door and saw a heat wave rolling in the room, and he was surrounded by a sense of asphyxiation caused by burning.

But when he took off his VR helmet, it all ended.

This is a simulation experience. None of those perceptual changes, whether hot or cold, or the numbness and stretching of hands and feet, really came from the environment in which he was living. What he felt was caused by several chemicals coming into contact with the skin through a wearable device: the numbness and stiffness of the arms because of the contact with the skin of Ricadoine; the oncoming heat wave because of the release of capsaicin to the face; the tingling sensation came from capsaicin, and the final cold feeling was caused by menthol.

This amazing wearable device uses a technology called Chemical Touch (chemical haptics). In fact, chemicals have always been used to understand tactile mechanisms. In the 1990s, studies on menthol and capsaicin helped us clarify how the body responds to hot and cold stimuli. Now Jasmine Lu of the University of Chicago and her colleagues are applying this knowledge to create a "sense of touch" induced by chemicals.

Use wearable devices to experience real "touch" in VR Source: Chemical Haptics: Rendering Haptic Sensations via Topical Stimulants, YouTube tactile, not only touch the word Haptics, directly translated as "touch", it can refer to any meaning related to touch, touch, but now it is more often used as an acronym for tactile technology. Tactile technology can produce a sense of touch without direct contact. It is not a new word, and devices with tactile technology can be seen everywhere in daily life. For example, the home key on iPhone 7 is not a physical button, it cannot be pressed, but is "pretending" to be pressed by sensing vibration-perhaps the most common application of haptic technology around us.

The application of tactile technology is much more than a small mobile phone button. Tactile devices can help stroke patients regain the sensation of their arms, and it can also provide realistic tactile feedback for medical students' cardiopulmonary resuscitation training. In 2019, Hong Kong researchers developed a virtual skin that can "hug" relatives around the world.

The limitation of such devices is that most of them function by force or vibration, so they can only use one form of tactile mechanism-stress, and our skin can sense much more than stress. For example, if you touch a piece of ice and a soldering iron (if you can get a hard hand), it is obvious that the two objects give you a different feeling, indicating that in addition to stress, your skin also feels other types of irritation. Touch is produced by a variety of receptors in the skin. The skin has thermoreceptors to sense heat and cold, mechanical receptors to sense vibration and pressure, and nociceptive receptors to sense pain. So, if you can simulate all these feelings and integrate them into the same device, you can replicate an extremely realistic sense of touch.

The purpose of chemical tactile technology is to use chemicals to simulate these "packages" of cold, heat, vibration, pressure and so on. This plan is feasible. Jas Brooks, who is on the same team as Jasmine Lu, previously designed a VR helmet that releases chemicals such as menthol and capsaicin to the trigeminal nerve in the nasal cavity, which then conveys hot and cold sensations (that is, temperature information) to the brain. Moreover, users not only associate hot and cold because of the smell of menthol or capsaicin, but also because the trigeminal nerve is clearly "telling" the brain that the temperature of the environment has changed.

By giving users chemical stimulation on the skin, let them feel different forms of "touch", can now achieve tingling, numbness, cool, warm feeling. Picture source: reference [2]

But to tell you the truth, using this device is really looking for abuse, so that capsaicin is pumped directly into the nasal cavity, and the feeling of heat is very accurate, and it is enough to think about the feeling that it is so hot that it goes straight to Tianlinggai. Obviously, although this device is effective, few people will want to use it. So Jasmine Lu is looking for a way to bypass the nose and create a sense of touch directly through the skin. So how do chemicals act on the skin to produce sensations? Coincidentally, someone has already answered this question perfectly.

Lessons from capsaicin and menthol in the early 1990s, David David Julius of the University of California, California, was looking for an alternative to opioid painkillers. But first, he needs to understand molecular biology how the body senses pain and how tactile signaling pathways are enhanced.

He and his colleagues created a library of millions of DNA fragments, each corresponding to genes in neurons that respond to pain, heat and touch. Since capsaicin gives the skin a burning sensation, there must be receptors on the cells that respond to capsaicin, and there must be genes in these DNA fragments that encode the receptor protein. After a long period of research, in 1997, they finally identified a receptor called TRPV1. TRPV1 is located on the cell membrane of nociceptive neurons. When stimulated by capsaicin, TRPV1 will open ion channels in response. Interestingly, TRPV1 is also activated by thermal stimulation, and when exposed to temperatures above 43 ℃, TRPV1 releases exactly the same electrical signals to the brain-so "hot" and "hot" make us feel very similar.

This conclusion can explain a lot about spicy phenomena. We often mention "ups and downs" together, but in fact, when we think about it, we can see that spicy is obviously different from the other three flavors. For example, if you rub your eyes with a hand that has just cut chili peppers, your eyes will feel hot, but if you rub your eyes with a hand that has just touched the cake, your eyes will not feel sweet. Also, when you eat hot pot in winter, you feel spicy in your mouth and feel warmer and warmer on your body. These examples all remind us that there is a similar relationship between spicy and hot, spicy is not a kind of taste, it is essentially a kind of "heat".

David Julius and others continued to spend years studying in detail the complex system of receptors, neurons, receptors and ion channels from which our endless and wonderful tactile sensations come from. Arden Pataptien (Ardem Patapoutian), another central figure in the study, used menthol to discover the mechanism by which the skin produces a "cold sensation", followed by baroreceptors on the skin. This work has led to a gradual understanding of what touch is. In 2021, David Julius and Ardem Patapoutian won the Nobel Prize in Physiology and Medicine for their discovery of temperature and tactile receptors.

Jasmine Lu was also inspired by their work, so she redesigned the experimental scheme. Instead of creating a thermal environment, exerting force or vibration to achieve tactile technology, she tries to use chemicals to directly stimulate the skin and trigger receptors in the skin to simulate tactile sensations.

2021 Nobel Laureate in Physiology or Medicine David Julius (left) and Arden Pataptien Photo Source: Twitter@ardemp 's third "chemical sensation" We can sense stimuli from chemicals because receptors in cells interact with chemical molecules and then respond and transmit signals to the brain. In most people's inherent cognition, this process is mainly embodied in the sense of smell and taste. However, if your mind stays here, you obviously underestimate the receptor.

The receptor for smell is in the nasal cavity, and the receptor for taste is on the tongue. In fact, you can imagine that there is a third "chemical sensation" even without the nose and tongue. For example, put on the essential oil, you will feel cool, this is the effect of menthol, and this effect does not pass through the nose and tongue at all. For example, when you chew pepper, not only do you have a spicy mouth, but your lips also feel like needles, because there is a key ingredient in pepper called capsicinol. it interacts with pain receptors and mechanical receptors (especially those that sense vibration) on the lip skin, as if there is a small vibrating motor on your lips, so you will feel a tingling sensation. It can be seen that the receptors that respond to chemical stimuli exist not only in the nose and tongue, but also in the sense of smell and taste.

So, how to define, name and describe this third "chemical feeling"?

In 1912, American zoologist George H. Parker put forward the concept of "common chemical sensation", which is used to describe the chemosensory of animals (especially skin). Through animal experiments, Parker believes that this is a property that widely exists in the nervous system rather than taste and olfactory nerves. Studies in the 1950s have shown that this "common chemical sensation" is at least partly mediated by the receptors of pain receptors, and that "common chemical perception" is actually a special kind of pain. The above-mentioned studies on capsaicin and menthol have also made people realize that "common chemical sensation" and temperature sensation may be the same thing. It was not until the 1990s that someone proposed to use the concept of "chemical physical perception" (chemesthesis) instead of "common chemical sense" to describe this third chemical sense. By definition, chemical physical perception is a kind of somatosensory with the characteristics of pain, temperature and touch.

It is not difficult to find that there is a certain overlap in meaning between chemical physical sense and chemical sense of touch. But whatever its name, you have long been a "consumer" of this concept. Some of the ointments you buy will use high concentrations of holly oil (containing peppermint) to create an endothermic reaction on the skin to relieve pain; some of the skin care products you use will use capsaicin to promote blood circulation; most of the toothpaste you use every day comes from menthol.

There are prospects and limitations. Now, Jasmine Lu's team has applied this chemical tactile technology to VR. They created a wearable device that stores chemicals in the wearable device and pushes the channels that are open to the skin through micropumps, allowing the skin to come into contact with or even absorb reagents as they pass through, creating sensations: capsaicin is used to create tingling sensations, capsaicin is used to simulate heat, menthol is used to create cold sensations, cinnamaldehyde is used to cause itching. Lidocaine, a common anesthetic, can make the skin numb and stiff. Therefore, it can help create a realistic virtual world. This is undoubtedly exciting news for players who travel around the game world. But can we completely replace the real sense of touch with this experience? If not, what is the difference between these two senses of touch?

At the 2021 user Interface Software and Technology Conference (User Interface Software and Technology conference), they released a video of a virtual reality scene in which a person wearing a wearable device they designed was "experiencing" a thrilling nuclear accident-the scene at the beginning of this article.

However, not everyone is excited about the technology, and even not everyone agrees with its meaning. At least in the eyes of practitioners in some fields, touch is a sociological behavior that is not only an action, but sometimes symbolizes an emotional connection. It cannot be simply and rudely summed up and replaced by cold, heat, pain, and numbness-for example, the feeling of touching the cat's hair with your fingers while stroking the cat is gentle and soothing and very decompressed, which is difficult to replicate with several chemicals.

These skeptical voices also reveal the limitations of this technology. Why is stroking a cat so decompressed? The answer lies in the nerve fibers that mediate this type of touch. Unlike the sense of touch that senses cold or heat, pain or itching (known as discriminative touch, or discriminative touch), touch when stroking a cat is an emotional touch (affective touch), which is dominated by a special nerve fiber, the CT fiber. CT fibers respond only to slow, gentle touches, such as touch stimuli that move about 5 centimeters per second. Touching when stroking a cat is this type of stimulation, and so is the frequency at which we are most comfortable with massage. As the name implies, it is called "emotional" touch because it can be related to people's psychological function and emotional experience. What Jasmine Lu's chemical tactile system can simulate is discriminative tactile, which is powerless to emotional tactile. This is indeed the limitation of chemical tactile technology, which cannot really simulate tactile sensation in all directions in principle. Even so, its prospects are promising.

In fact, many people have misunderstandings about this technology. Chemical tactile technology is not meant to replace real touch, just like no matter how lifelike VR is, no one will think that they can live in VR. The real application scenario of chemical tactile devices is that they can enhance the experience in the digital world, allowing us to do and experience things that we can't do in our daily lives-- such as replacing part of the training of firefighters. Because it can simulate some of the feelings in the sea of fire, but not really in the sea of fire.

Or we can say that this chemical tactile technology developed by the Jasmine Lu team is mutual achievement with the development of the VR field. In fact, people's experience in virtual reality is realistic enough, and that's why "meta-universe" has become one of the hottest concepts at the moment, but if we want to achieve a feeling comparable to that of the real world, we may also need to simulate richer and more diverse senses beyond sight and hearing-- a complete and comprehensive one, to be exact. Including cold, heat, pain, numbness and other "discriminative touch" and comfortable "emotional touch".

references

[1] Artificial touch: The new tech making virtual reality more immersive. New Scientist. Issue 3378.

[2] https://doi.org/10.1145/3472749.3474747

[3] https://www.nobelprize.org/uploads/2021/10/press-medicineprize2021.pdf

Product: popular science China

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