Let Your Fingers Do the Seeing

Humans can feel objects that are just nanometers thick, a new study says.

We can feel tiny details invisible to the naked eye, such as the grit of this high-end sandpaper.

Sandpaper. Colored scanning electron micrograph (SEM) of the surface of advanced sandpaper showing the regular pyramidal arrangement on its surface. Sandpaper is designed to smooth rough surfaces by taking off their upper layers, and this type consists of tiny raised pyramids which are highly durable and abrasive. Magnification: x15 at 6x7cm size.

Quick—name the five senses.

Most people readily list sight, taste, hearing, and smell. And then pause before remembering: touch.

"Touch is probably our most underrated sense," said psychologist Martin Arvidsson of Stockhom University in Sweden, whose research team has found that humans can perceive even smaller changes in surfaces than previously believed.

Touch matters, Arvidsson said.

He points to the importance of touch in understanding others: "Babies explore the world through touch and find comfort in human contact. The need for touch does not go away with age either: Think about affectionate touch such as hugs and kisses or sex." It can even be important in getting a job.

In a study published in today's Scientific Reports, the researchers report that humans can perceive miniscule changes in surfaces—down to a microscopic 13 nanometers, about the width of a human hair.

What happens when you touch something?

According to Mark Rutland, another researcher in the study and a professor at the KTH Royal Institute of Technology in Stockholm, touch is a sensation that relies on a combination of friction and vibrations.

When your finger rubs against another surface, tiny pressure sensors embedded within your fingers, called Pacinian corpuscles, perceive the texture.

These sensors also pick up vibrations, and the closer the vibrations are formed to these sensor areas, the stronger their sensitivity.

Vibrations felt by these pressure sensors add up to particular frequencies that the brain translates into our surprisingly fine sense of touch.

"You adjust the speed of your finger as you stroke, so your vibrational senses are able to detect these," Rutland said. "You can only sense these vibrations if you can feel the bumps."

How did the researchers test if people could feel such fine textures?

The research team recruited 20 women (more on that in a bit) to touch specially designed materials that were produced to be smooth and temperature resistant.

Each subject was blindfolded and then touched two separate materials. They were asked to rate how different the textures of the two materials were, with 100 percent considered no difference in texture and 0 percent meaning the materials felt completely different.

The results? The participants were able to feel differences in the two materials that were incredibly tiny, with the smallest being 13 nanometers.

So we didn't know much about touch before?

Not really. Scientists know surprisingly little about touch and how it works with our brains. And as our world relies more than ever on technology that requires swiping and sliding (so-called haptic tasks), touch is becoming increasingly important.

"The long-term goal of this is to find the tactile aesthetics you are capable of feeling," Rutland said, pointing to a need to understand "what sort of shapes and sizes we can perceive on the finger."

What's different?

Before this study, research on touch done without electrodes or animals was rare. The study takes an innovative approach by using human feedback.

"This is the first time that we can relate to touch and perception without needing to go through the need to put electrodes on [subjects'] brains," Rutland said. "We're directly taking the physical information on the surfaces and combining them on perception."

In other words, the researchers were able to measure not only how small a texture humans could feel, but also if they were accurately sensing textures.

Keep in mind the study included only women, who "are slightly better than men on haptic tasks," according to Arvidsson. They are "more likely to detect something with such small textures."

Why does this matter?

"You mean besides the coolness of the finding itself?" Arvidsson asked.

"There are plenty of rather small, naturally occurring stimuli in our environment," he said. "Take a single hair, for example. Not a massive structure, yet you could run your fingers along it and detect a defect."

Let's start with the basics: Humans can feel more precisely than previously understood. This means your tablet or smartphone experience may eventually go up a couple of notches—imagine being able to feel the swish of silk on your next online shopping adventure or turning the pages of your e-book and feeling paper under your fingers.

But the research team is looking beyond making your technological experience immersive.

"You can make buttons feel different as you stroke them," Rutland said. "This could help the visually impaired, make these technologies a lot easier to use."

Currently, most smartphones and tablets rely on sounds to guide visually impaired users. This research could be the first step to having them "feel" sounds instead.

"You could use [this research to create] all sorts of surfaces to build tactile responsive surfaces," Rutland said, explaining that different consumer products would both feel different and respond differently to a person's touch.

The future, apparently, is right at our fingertips.

Follow Tanya Basu on Twitter.