Human touch can detect even molecular differences

By PTI Published on Dec 18, 2017 01:33 PM IST

Los Angeles: The human touch is sensitive enough to feel the difference between surfaces that vary by just a single layer of molecules, according to scientists including one of Indian origin.

Humans can easily feel the difference between many everyday surfaces such as glass, metal, wood and plastic. That is because these surfaces have different textures or draw heat away from the finger at different rates.

However, researchers wanted to study if humans could detect the difference if they changed only the topmost layer of molecules. "This is the greatest tactile sensitivity that has ever been shown in humans," said Darren Lipomi, a professor at University of California (UC) San Diego in the US.

"Receptors processing sensations from our skin are phylogenetically the most ancient, but far from being primitive they have had time to evolve extraordinarily subtle strategies for discerning surfaces," said V S Ramachandran, from UC San Diego.

"This study is one of the first to demonstrate the range of sophistication and exquisite sensitivity of tactile sensations. It paves the way, perhaps, for a whole new approach to tactile psychophysics," Ramachandran said.

This fundamental knowledge will be useful for developing electronic skin, prosthetics that can feel, advanced haptic technology for virtual and augmented reality and more, researchers said.

Unsophisticated haptic technologies exist in the form of rumble packs in video game controllers or smartphones that shake, Lipomi said. "But reproducing realistic tactile sensations is difficult because we don't yet fully understand the basic ways in which materials interact with the sense of touch," said Lipomi. In the study published in the journal Materials Horizons, researchers tested whether human subjects could distinguish - by dragging or tapping a finger across the surface - between smooth silicon wafers that differed only in their single topmost layer of molecules. One surface was a single oxidised layer made mostly of oxygen atoms.

The other was a single Teflon-like layer made of fluorine and carbon atoms. Both surfaces looked identical and felt similar enough that some participants could not differentiate between them.

In one test, 15 participants were tasked with feeling three surfaces and identifying the one surface that differed from the other two. Subjects correctly identified the differences 71 per cent of the time. In another test, subjects were given three different strips of silicon wafer, each strip containing a different sequence of 8 patches of oxidised and Teflon-like surfaces. Each sequence represented an 8-digit string of 0s and 1s.

Subjects were asked to "read" these sequences by dragging a finger from one end of the strip to the other and noting which patches in the sequence were the oxidised surfaces and which were the Teflon-like surfaces. In this experiment, 10 out of 11 subjects decoded the bits more than 50 per cent of the time.

Subjects spent an average of 4.5 minutes to decode each letter. "A human may be slower than a nanobit per second in terms of reading digital information, but this experiment shows a potentially neat way to do chemical communications using our sense of touch instead of sight," Lipomi said.