The handheld devices use mechanical actuators and a 4x4 grid of pins to convey what it feels like to touch different objects, even taking surface hardness among different objects into account. In the video embedded below, you can even see someone flicking a ball and cube around using the admittedly hacky-looking gizmos. The team admits that despite the successes presented here it still isn't sure how much haptic feedback is needed to be convincing:
"On several occasions we observed people trying out our devices when they were not well calibrated (e.g., NormalTouch would render a surface normal in a drastically different direction than it was supposed to). To our surprise, people often claimed that the device accurately rendered the surface when in fact it was obviously incorrect. While anecdotal, this points to the need to further evaluate whether or not it is important to precisely match the haptic rendering in order for it to be considered realistic and high fidelity."
So, ultra-high fidelity might be overkill, much like pushing for photorealism in VR. The brain doesn't need "perfect" accuracy to be effectively tricked into thinking what it's seeing and sensing is real, the experience just needs to be "good enough."
If you want to dig deeper, the source research paper is surprisingly easy to digest and has a ton of additional details.
