A sense of touch could upgrade virtual reality, prosthetics and more

Researchers also hope to bring ‘touch’ to such things as online shopping and doctor visits

On most mornings, Jeremy D. Brown eats an avocado. But first, he gives it a little squeeze. A ripe avocado will yield to that pressure, but not too much. Brown also weighs the fruit in his hand. He feels the waxy skin’s bumps and ridges.

“I can’t imagine not having the sense of touch to be able to do something as simple as judging the ripeness of that avocado,” says Brown. He’s a mechanical engineer at Johns Hopkins University. That’s in Baltimore, Md. Brown studies haptic feedback. That’s information conveyed through touch.

Many of us have thought about touch more than usual during the COVID-19 pandemic. Hugs and high fives have been rare. More online shopping has meant fewer chances to touch things before buying. People have missed out on trips to the beach where they might have sifted sand through their fingers. A lot goes into each of those sensory acts. Our sense of touch is very complex. Every sensation arises from thousands of nerve fibers and millions of brain cells, explains Sliman Bensmaia. He’s a neuroscientist at the University of Chicago in Illinois. Nerve receptors detect cues about pressure, shape, motion, texture, temperature and more. Those cues activate nerve cells, or neurons. The central nervous system interprets those patterns of activity. It tells you if something is smooth or rough, wet or dry, moving or still.

Neuroscience is at the heart of research on touch. But Brown and other engineers study touch, too. So do experts in math and materials science. They want to translate the science of touch into helpful applications. Their work may lead to new technologies that mimic tactile sensations. Some scientists are learning more about how our nervous system responds to touch. Others are studying how our skin interacts with different materials. Still others want to know how to produce and send simulated touch sensations.

All these efforts present challenges. But progress is underway. And the potential impacts are broad. Virtual reality may get more realistic. Online shoppers might someday “touch” products before buying them. Doctors could give physical exams online. And people who have lost limbs might regain some sensation through prostheses. “Corduroy will produce one set of vibrations,” Bensmaia says. Types of silk produce other sets. Scientists can measure those sets of vibrations. That work is a first step toward reproducing the feel of different textures.

But creating the right vibration pattern is not enough. Any stimulation meant to mimic a texture must be strong enough to trigger the skin’s touch receptors. And researchers are still figuring out how strong is strong enough.

For instance, vibrations caused by textures create different types of wave energy. One team found that rolling-type waves called Rayleigh (RAY-lee) waves go deep enough to reach Pacinian receptors. (Much larger versions of those waves ripple through Earth during earthquakes.) The team shared this finding last October in Science Advances. The size of Rayleigh waves also matters. For the most part, those waves must be at least 2.5 times as long as the depth of those Pacinian receptors in the skin. That’s enough for a person — and most other mammals — to feel a sense of touch through those receptors, explains James Andrews. He’s a mathematician at the University of Birmingham in England. His team discovered this rule by looking at studies that involved animals — including dogs, dolphins and rhinos.

This work helps reveal what it takes to realistically capture touch, Andrews says. New devices could use such information to convey touch sensations to users. Some might do this using ultrasonic waves or other techniques. And that might someday lead to virtual hugs and other tactile experiences in virtual reality. Cynthia Hipwell moved into a new house before the pandemic. She looked at some couches online but she couldn’t bring herself to buy one from a website. “I didn’t want to choose couch fabric without feeling it,” says Hipwell. A mechanical engineer, she works at Texas A&M University in College Station.

She imagines that one day, “if you’re shopping on Amazon, you could feel fabric.” We’re not there yet. But touch screens that mimic different textures are being developed. What may make them possible is harnessing shifts in electrical charge or vibrations. Touching the screen would then tell you whether a sweater is soft or scratchy. Or if a couch’s fabric feels bumpy or smooth. Future haptic technology will likely need substantial refining to get things right. And virtual hugs and other simulated touch may never be as good as the real thing. But haptics may provide new ways to explore our world and stay in touch — both literally and virtually.