New perceptual illusion: How the index finger can be fooled

Developing a virtual sense of touch is the long-term aim of Professor Dr. Marc Ernst, who headed the Cognitive Neurosciences research group in Bielefeld until the end of March 2016." On the EU research project "WEARHAP," Ernst is working with colleagues from all around Europe to achieve this goal. "We now have a better understanding of how we can virtually convey the impression of whether an object feels soft or hard," explains the neuroscientist. "In the future, this should help in developing a virtual sense of touch with which one can 'touch' things across distances, such as how a sweater or another product feels while shopping online."

"A fundamental question in this project is what role haptic stimuli play in perception," says Ernst. With the term 'haptic stimuli,' the cognitive scientist is referring to the sensations that arise from touch. "A special feature of our finger pads is that they are fleshy -- they can 'deform' by giving way when touching something," says Marc Ernst. For instance, when a person touches a sponge, she feels its composition and consistency through the tactile sensors in her skin.

For their experiment, the researchers constructed an apparatus at the end of which an elastic fabric strap was stretched horizontally. The tightness of the strap was adjustable. The test subject laid her hand and lower arm in the guiding casing of the apparatus. The person was instructed to say when they thought their finger was bent more. In reality, the position of the finger did only change a little -- only the tightness of the elastic band did. "Astonishingly, all study participants estimated their finger to be most bent when the elastic band was loose. This is apparently because the loose band has comparatively more contact area with the skin," explains Dr. Alessandro Moscatelli, who performed the experiment.

"The key here is how much surface area of the object comes into contact with our skin. The greater the area of contact, the closer the object seems to be, and therefore, the more the finger appears to be bent. Why is this finding significant? "If we were not to know exactly how our body is positioned, we would not be able to grasp or catch, and therefore could not interact with objects or other people," explains Marc Ernst.

Bielefeld University is cooperating with research institutions from across Europe on the research project WEARHAP (WEARable HAPtics for Humans and Robots), which will run until February 2017. The European Union has invested 7.7 million Euro in this project, of which almost 1 million Euro is going to Bielefeld University.