We like the soft feel of a cat’s fur, but we don’t like mud, which is slimy, nearly as much. Why is this? We are told that everyone’s tastes are different. But that does not keep scientists from trying to find answers. Jenny Faucheu, a researcher at Mines Saint-Étienne, has studied tactile perception, a highly original subject.
“We’re used to defining what is beautiful or pleasant from a visual perspective,” explains Jenny Faucheu, a materials engineering researcher at Mines Saint-Étienne, “but it is less common to think about these questions in terms of other senses, such as touch.” A Research Group name GDR TACT 2033 was formed on 1 January 2018 to study the complexity of tactile perception across a wide range of disciplines.
A better understanding of the sense of touch would provide a wide range of benefits. On one hand, medical examination focused on the possible causes of tactile deficiency or applications focused on rehabilitation. And on the other hand, efforts to develop and design products geared to tactile interfaces and simulators, or innovation in e-commerce. To make this possible, insight must be gained into a sense that is often considered of secondary importance, after sight or hearing.
Who likes what
“Our goal is not to define a human standard and a perfect material,” says Jenny Faucheu, “we’re trying to create links between different aspects through tactile perceptions.” The researchers therefore take the material’s texture and substance into account by using sensors to detect finger vibrations on a surface. They also study cerebral activity through electroencephalograms and collect behavioral information using psycho-sensory questionnaires. “For example, we wondered if it bothered people that they couldn’t feel the fabric when buying an item such as a sweater online.” explains Jenny Faucheu.
Other questionnaires were focused on the surfaces themselves. In a multiple-choice format, participants had to sort surfaces into four categories ranging from “I like it a lot” to “I really don’t like it.” Another focused instead on how surprising or familiar participants found a surface to be. They were then asked to sort the materials based on their similarities. Then, they were asked to name them and attribute labels for their characteristics. “These mechanisms allow us to create correspondences,” explains Jenny Faucheu, “so we can then say, if this person likes sample 22, they should like sample 45.”
Still, some materials win a consensus. People generally like smooth materials and like rough materials much less. And a surprise can be either positive or negative. But the cultural impact must be kept in mind. “This study was carried out with French participants,” she explains, “it is highly likely that the results would be different for a different culture.”
Liking without touching
To carry out this study, the research team made special surfaces. The various textures were created by distributing small cylindrical dots of varying heights, diameter and spacing on polyurethane surface. Certain samples were perceived as smooth, rough, vibrating or sticky.
“When we rub a sample, vibrations are generated and travel through our finger to the mechanoreceptors,” explains Jenny Faucheu. The sensors used by the research team make it possible to study the vibrations received by these sensory receptors in our fingers. The lowest frequencies correspond to rough materials, which are generally disliked. And, conversely, the higher the frequencies are, the more the materials are perceived as smooth and tend to be well-liked. But it would also appear that a high amplitude intensifies the feeling of roughness.
All fifty or so samples look alike from a visual perspective, with their whitish color, and the naked eye cannot make out the small bumps on some of them. “We also decided to perform the study in a room that was dark enough to limit the influence of sight,” says the Mines Saint-Étienne researcher. Visual information is omnipresent and can therefore interfere with our perception. But hearing can too, although in a more discreet manner.
“We wanted to know whether tactile perceptions would be modified by associating more or less enjoyable sounds,” adds Jenny Faucheu. The same experiments are therefore repeated but with soundproof headphones. When the tester runs his finger along the surface, various sounds are sent to the headphones. It would therefore seem to be conceivable to reverse the perception of a surface by adjusting the ambient sound. “That said, we’re talking about an unpleasant feeling, not a painful one,” she says.
The loss of tactile sensation may appear with age or following an accident. Tactile simulation exercises can be performed to help slow down this loss or regain this sensation. It is possible that an unpleasant feel could slow rehabilitation by requiring additional effort. Therefore, relying on the sense of hearing to transform the perception of a surface could facilitate this process. “It’s the principle of gameification, ” says Jenny Faucheu, “the more fun and enjoyable the process, the more the patient is engaged and the rehabilitation is effective.” An idea that requires fundamental research on the sense of touch and new protocols for analyzing and understanding.
The same principle applies to tactile interfaces. On a tablet or smartphone, there is usually tactile feedback to emphasize a selection: a tool that improves interaction with the object. “Tactile simulators try to simulate real renderings of surfaces,” adds Jenny Faucheu. Projects such as StimTact aim to develop an augmented tactile screen that gives people the impression that they are touching the material displayed. We could therefore imagine buying a sweater on an online shopping website and caressing the real surface of the fabric, from right in front of our computer. Jenny Faucheu is a researcher at the Georges Friedel laboratory, a joint research unit between CNRS and Mines Saint-Étienne.
Tiphaine Claveau for I’MTech