Double the Fun

Simulating tactile experiences in virtual reality (VR) has been a major challenge, but recent advancements have brought us closer to achieving truly immersive sensations, especially when it comes to touching and manipulating objects with our hands. One of the key aspects of realistic haptic feedback is the ability to convey the sense of touch and texture to users, allowing them to interact with virtual objects in a way that closely mimics the physical world. To achieve this, stimulating multiple fingertips simultaneously is essential, as our sense of touch is highly nuanced and relies on the coordination of various sensory inputs.

In VR, pinching is one of the most common hand gestures used for interaction. In these cases, the thumb and forefinger come together to grasp objects or otherwise control the experience. However, it has been difficult to achieve convincing haptic feedback for pinching. Traditional vibrotactile feedback devices, which are often attached to gloves or other controllers, are relatively large and do not allow the fingers to come together fully. This limitation not only hinders the naturalness of interaction, but also affects the user's perception of object shape and texture.

Furthermore, these traditional haptic devices often struggle to provide distinct sensations to individual fingertips as they come into contact with virtual objects. This deficiency breaks the illusion of reality, making it challenging for users to suspend their disbelief and fully engage in the VR experience. To create a truly immersive and convincing tactile experience in VR, researchers and developers must have finer control over where sensations are perceived.

A trio of researchers at Saarland University and The University of Sydney have developed a relatively simple electrotactile device that could greatly enhance future VR experiences. Their creation consists of thin, flexible sheets of electrodes that can be attached to the fingertips. Each pad is thin enough to allow fingers to be fully pinched together, and importantly, they are double-sided. This feature allows a developer to specify a different pattern of stimulation for each finger.

The devices were produced by printing silver nanoparticle-based conductive ink, with an inkjet printer, on a coated paper to create the traces and electrodes. A pair of these sheets are joined, back-to-back, using double-sided adhesive tape. In order for the electrodes to make good contact with the skin, z-axis conductive tape was affixed to the surface of the sheets, then pads of copper tape (produced with a craft cutter) were attached to the skin-facing side. Finally, an insulating layer was placed on top of the traces for protection, leaving only the electrodes exposed to the skin.

To control the circuit, each electrode trace was attached to a flat flexible cable via the z-axis tape. A custom control circuit was designed to deliver current to each electrode ranging from 0 to 2.7 milliamps, with 200 discrete steps in the range. Using this interface, the team showed that it was possible to provide stimulation on one side, like traditional devices, but also to stimulate both sides in different ways, opening up opportunities for new types of experiences. They also showed that by moving the location of the stimulation over time, they could simulate the sensation of movement, as if an object was slipping through one’s fingertips.

A pair of small user studies were conducted to assess users’ ability to differentiate between the various stimulation modes. The study participants confirmed that they could tell the difference between single- and double-sided stimulation, and also that it resulted in a qualitative difference in tactile sensation. The ability of the device to simulate motion was also confirmed in the study.

A few simple VR applications were then developed which showed the real-world utility of the system. However, the researchers note that only very basic patterns of stimulation were explored, and intend to extend their work in the future. The wiring also looks to be a bit cumbersome, so hopefully a future wireless version will be developed. With refinement, an interface such as this has the potential to significantly improve VR experiences.