What does a robot feel when it touches something? Little or nothing until now. But with the right sensors, actuators and software, robots can be given the sense of feel — or at least the ability to identify materials by touch.

Researchers at the University of Southern California have published a study in Frontiers in Neurorobotics showing that a specially designed robot can outperform humans in identifying a wide range of natural materials according to their textures, paving the way for advancements in prostheses, personal assistive robots and consumer product testing.

The robot was equipped with a new type of tactile sensor built to mimic the human fingertip. It also used a newly designed algorithm to make decisions about how to explore the outside world by imitating human strategies.

Capable of other human sensations, the sensor can also tell where and in which direction forces are applied to the fingertip and even the thermal properties of an object being touched.

Like the human finger, the group’s BioTac sensor has a soft, flexible skin over a liquid filling. The skin even has fingerprints on its surface, greatly enhancing its sensitivity to vibration.

As the finger slides over a textured surface, the skin vibrates in characteristic ways. These vibrations are detected by a hydrophone inside the bone-like core of the finger. The human finger uses similar vibrations to identify textures, but the BioTac is even more sensitive.

When humans try to identify an object by touch, they use a wide range of exploratory movements based on their prior experience with similar objects. A famous theorem by 18th century mathematician Thomas Bayes describes how decisions might be made from the information obtained during these movements.

Until now, however, there was no way to decide which exploratory movement to make next. The article, authored by Gerald Loeb and Jeremy Fishel, describes their new theorem for this general problem as “Bayesian Exploration.”

Built by Fishel, the specialised robot was trained on 117 common materials gathered from fabric, stationery and hardware stores. When confronted with one material at random, the robot could correctly identify the material 95 per cent of the time, after intelligently selecting and making an average of five exploratory movements. It was only rarely confused by a pair of similar textures that human subjects making their own exploratory movements could not distinguish at all.

So, is touch another task that humans will outsource to robots? Fishel and Loeb point out that while their robot is very good at identifying textures, it has no way to tell what textures people will prefer. Instead, they say this robot touch technology could be used in human prostheses or to assist companies who employ experts to judge the feel of consumer products and even human skin.